JGRG 33
Quintessential interpretation of the evolving dark energy in light of DESI observations ▼
The recent result of Dark Energy Spectroscopic Instrument (DESI) in combination with other cosmological data shows evidence of the evolving dark energy parameterized by w0waCDM model. We interpret this result in terms of a quintessential scalar field and demonstrate that it can explain the DESI result even though it becomes eventually phantom in the past. Relaxing the assumption on the functional form of the equation-of-state parameter w=w(a), we also discuss a more realistic quintessential model. The implications of the DESI result for Swampland conjectures, cosmic birefringence, and the fate of the Universe are discussed as well.
Primordial black holes and induced gravitational waves from logarithmic non-Gaussianity
R. Inui, C. Joana, H. Motohashi, S. Pi, Y. Tada and S. Yokoyama
arXiv:
2411.07647
[astro-ph.CO].
Towards a classification of UV completable Higgs inflation in metric-affine gravity
Y. Mikura and Y. Tada
arXiv:
2410.11277
[hep-th].
I'm a theoretical scientist in Nagoya University, Japan. My main interest is the physics of the early stage of our universe. In particular, I have so far focused on inflation, the accelerated expansion preceding the hot Big-Bang universe. I have proposed a novel analyzing approach to inflation with use of mathematics of random noise called stochastic calculus. Primordial black hole is also my research topic as a direct consequence of particular dynamics of the early universe. I'm working on several production mechanism of gravitational waves as well. I'm from Saitama, Japan. I completed B.Sc. in Physics in 2012 and M.Sc. in Physics in 2014, and received Ph.D. in Physics from the University of Tokyo in March 2017.
Yuichiro Tada
ES bldg. 604, Nagoya University
Furocho Chikusaku Nagoya, Aichi 464-8602 Japan
+81 (0)80-9566-9181
tada.yuichiro.y8@f.mail.nagoya-u.ac.jp
Ph.D. in Physics
•
23rd March 2017
Department of Physics, Adviser:
Dr. Masahiro Kawasaki & Dr. Hitoshi Murayama
M.Sc. in Physics
•
24th March 2014
Department of Physics, Adviser:
Dr. Masahiro Kawasaki & Dr. Hitoshi Murayama
B.Sc. in Physics
•
23rd March 2012
Department of Phyiscs
Graduate • March 2008
Designated Assistant Professor
•
April 2021–Present
Institute for Advanced Research & Department of Physics, C-lab.
Associate Researcher
•
April 2022–March 2023
Institute of Particle and Nuclear Studies
Lecturer (part-time)
•
April 2019–March 2021
Classical mechanics 1, 2
JSPS Fellow (PD)
•
April 2018–March 2021
C-lab., Department of Physics
PD researcher
•
April 2017–March 2018
Dr. Sébastien Renaux-Petel's Group
JSPS Fellow (DC2)
•
April 2015–March 2017
Kavli IPMU & ICRR
ALPS Fellow
•
October 2012–March 2017
Kavli IPMU & ICRR
We have proposed a new analysis method for inflation with use of stochastic culculus, mathematics of random noise. This enable a non-perturbative calculation of primordial curvature fluctuations. We have re-formulate it in a fully covariant way, and working on its application to, e.g., primordial black hole. Inflation, Stochastic Culc., Curvature PTB., PBH
Primordial black holes (PBHs) are hypothetical black holes formed in the very early universe. They are a candidate of dark matter as well as a source of merger gravitational waves detected by LIGO/Virgo observatories. We have suggested that PBH can be easily realized if inflation happens many times. We have also investigated its spatial distribution in the bias theory.
Dark Matter, Gravitational Wave, Inflation, BiasGravitational wave (GW) is the wave of spacetime. In 2015, LIGO/Virgo observatories finally succeeded to directly detect this 'Einstein's last homework'. It can be also connected to physics of the early universe. We are working on several 'GW genesis' in inflation as well as cosmological 'magnetogenesis'. We are also interested in the possibility that GWs can probe the cosmic phase transition of quantum chromodynamics.
Chirality, MagnetogenesisStatistical properties of cosmological perturbations are important information of the early universe. However they can be distorted, called 'Local Observer Effect (LOE)', because density perturbation affects the physical scale itself in general relativity. We have formulated the computational program which is free from this LOE.
Cosmological PTB.Proin gravida nibh vel velit auctor aliquet. Aenean sollicitudin, lorem quis bibendum auctor, nisi elit consequat ipsum, nec sagittis sem nibh id elit.
PhotographyProin gravida nibh vel velit auctor aliquet. Aenean sollicitudin, lorem quis bibendum auctor, nisi elit consequat ipsum, nec sagittis sem nibh id elit.
Branding, Illustration
[48]
Primordial black holes and induced gravitational waves from logarithmic non-Gaussianity
R. Inui, C. Joana, H. Motohashi, S. Pi, Y. Tada and S. Yokoyama
arXiv:
2411.07647
[astro-ph.CO].
[47]
Towards a classification of UV completable Higgs inflation in metric-affine gravity
Y. Mikura and Y. Tada
arXiv:
2410.11277
[hep-th].
[46]
Improved quantum algorithm for calculating eigenvalues of differential operators and its application to estimating the decay rate of the perturbation distribution tail in stochastic inflation
K. Miyamoto and Y. Tada
arXiv:
2410.02276
[quant-ph].
[45]
Constant roll and non-Gaussian tail in light of logarithmic duality
R. Inui, H. Motohashi, S. Pi, Y. Tada and S. Yokoyama
arXiv:
2409.13500
[astro-ph.CO].
[44]
STOLAS: STOchastic LAttice Simulation of cosmic inflation
Y. Mizuguchi, T. Murata and Y. Tada
arXiv:
2405.10692
[astro-ph.CO].
[43]
Multifield Stochastic Dynamics in GUT Hybrid Inflation and Gravitational Wave Signatures of GUT Higgs Representation
Y. Tada and M. Yamada
Phys. Lett. B 855 (2024), 138854
[arXiv:
2405.08859
[hep-ph]].
[42]
The LISA forecast on a smooth crossover beyond the Standard Model through the scalar-induced gravitational waves
A. Escriva, R. Inui, Y. Tada and C. M. Yoo
arXiv:
2404.12591
[astro-ph.CO].
[41]
Quintessential interpretation of the evolving dark energy in light of DESI
Y. Tada and T. Terada
Phys. Rev. D 109 (2024) no.12, L121305
[arXiv:
2404.05722
[astro-ph.CO]].
[40]
Prospects of detection of subsolar mass primordial black hole and white dwarf binary mergers
T. S. Yamamoto, R. Inui, Y. Tada and S. Yokoyama
Phys. Rev. D 109 (2024) no.10, 103514
[arXiv:
2401.00044
[gr-qc]].
[39]
Primordial Black Holes and induced gravitational waves from a smooth crossover beyond Standard Model
A. Escrivà, Y. Tada and C. M. Yoo
arXiv:
2311.17760
[astro-ph.CO].
[38]
Cancellation of quantum corrections on the soft curvature perturbations
Y. Tada, T. Terada and J. Tokuda
JHEP 01 (2024), 105
[arXiv:
2308.04732
[hep-th]].
[37]
Translating nano-Hertz gravitational wave background into primordial perturbations taking account of the cosmological QCD phase transition
K. T. Abe and Y. Tada
Phys. Rev. D 108 (2023) no.10, L101304
[arXiv:
2307.01653
[astro-ph.CO]].
[36]
Stochastic dynamics of multi-waterfall hybrid inflation and formation of primordial black holes
Y. Tada and M. Yamada
JCAP 11 (2023), 089
[arXiv:
2306.07324
[astro-ph.CO]].
[35]
Primordial black hole formation in hybrid inflation
Y. Tada and M. Yamada
Phys. Rev. D 107, no.12, 123539 (2023)
[arXiv:
2304.01249
[astro-ph.CO]].
[34]
Squeezed bispectrum and one-loop corrections in transient constant-roll inflation
H. Motohashi and Y.Tada
JCAP 08 (2023), 069
[arXiv:
2303.16035
[astro-ph.CO]].
[33]
Primordial Black Holes
A. Escrivà, F. Kuhnel and Y. Tada
Black Holes in the Era of Gravitational-Wave Astronomy, Elsevier, 2024, 261-377
[arXiv:
2211.05767
[astro-ph.CO]].
[32]
Primordial black holes and gravitational waves induced by exponential-tailed perturbations
K. T. Abe, R. Inui, Y. Tada and S. Yokoyama
JCAP 05, 044 (2023)
[arXiv:
2209.13891
[astro-ph.CO]].
[31]
Hybrid metric-Palatini Higgs inflation
M. He, Y. Mikura and Y. Tada
JCAP 05, 047 (2023)
[arXiv:
2209.11051
[hep-th]].
[30]
Effective inspiral spin distribution of primordial black hole binaries
Y. Koga, T. Harada, Y. Tada, S. Yokoyama and C. M. Yoo
Astrophys. J. 939, no.2, 65 (2022)
[arXiv:
2208.00696
[gr-qc]].
[29]
Stochastic formalism for U(1) gauge fields in axion inflation
T. Fujita, K. Mukaida and Y. Tada
JCAP 12 (2022), 026
[arXiv:
2206.12218
[astro-ph.CO]].
[28]
Effective treatment of U(1) gauge field and charged particles in axion inflation
T. Fujita, J. Kume, K. Mukaida and Y. Tada
JCAP 09 (2022), 023
[arXiv:
2204.01180
[hep-ph]].
[27]
Simulation of Primordial Black Holes with large negative non-Gaussianity
A. Escrivà, Y. Tada, S. Yokoyama and C. M. Yoo
JCAP 05 (2022), no.05, 012
[arXiv:
2202.01028
[astro-ph.CO]].
[26]
Statistics of coarse-grained cosmological fields in stochastic inflation
Y. Tada and V. Vennin
JCAP 02 (2022), no.02, 021
[arXiv:
2111.15280
[astro-ph.CO]].
[25]
On UV-completion of Palatini-Higgs inflation
Y. Mikura and Y. Tada
JCAP 05 (2022), no.05, 035
[arXiv:
2110.03925
[hep-ph]].
[24]
Primordial black holes in peak theory with a non-Gaussian tail
N. Kitajima, Y. Tada, S. Yokoyama and C. M. Yoo
JCAP 10 (2021), 053
[arXiv:
2109.00791
[astro-ph.CO]].
[23]
Minimal $k$-inflation in light of the conformal metric-affine geometry
Y. Mikura, Y. Tada and S. Yokoyama
Phys. Rev. D 103 (2021), no.10, L101303
[arXiv:
2103.13045
[hep-th]].
[22]
Revisiting non-Gaussianity in non-attractor inflation models in the light of the cosmological soft theorem
T. Suyama, Y. Tada and M. Yamaguchi
PTEP 2021 (2021), no. 7, 073E02
[arXiv:
2101.10682
[hep-th]].
[21]
Induced gravitational waves as a cosmological probe of the sound speed during the QCD phase transition
K. T. Abe, Y. Tada and I. Ueda
JCAP 06 (2021), 048
[arXiv:
2010.06193
[astro-ph.CO]].
[20]
Local observer effect on the cosmological soft theorem
T. Suyama, Y. Tada and M. Yamaguchi
PTEP 2020 (2020), no.11, 113E01
[arXiv:
2008.13364
[astro-ph.CO]].
[19]
A manifestly covariant theory of multifield stochastic inflation in phase space
L. Pinol, S. Renaux-Petel and Y. Tada
JCAP 04 (2021), 048
[arXiv:
2008.07497
[astro-ph.CO]].
[18]
Conformal inflation in the metric-affine geometry
Y. Mikura, Y. Tada and S. Yokoyama
EPL 132 (2020), no.3, 39001
[arXiv:
2008.00628
[hep-th]].
Highlights of 2020
[17]
Escape from the swamp with spectator
K. Kogai and Y. Tada
Phys. Rev. D 101 (2020), no.10, 103514
[arXiv:
2003.06753
[astro-ph.CO]].
[16]
Stochastic inflation with an extremely large number of $e$-folds
N. Kitajima, Y. Tada and F. Takahashi
Phys. Lett. B 800 (2020), 135097
[arXiv:
1908.08694
[hep-ph]].
[15]
Primordial black hole tower: Dark matter, earth-mass, and LIGO black holes
Y. Tada and S. Yokoyama
Phys. Rev. D 100 (2019), no. 2, 023537
[arXiv:
1904.10298
[astro-ph.CO]].
[14]
Inflationary stochastic anomalies
L. Pinol, S. Renaux-Petel and Y. Tada
Class. Quant. Grav. 36 (2019), no. 7, 07LT01
[arXiv:
1806.10126
[gr-qc]].
Highlights of 2019–20
[13]
$\mathcal O(10) M_\odot$ primordial black holes and string axion dark matter
K. Inomata, M. Kawasaki, K. Mukaida, Y. Tada and T. T. Yanagida
Phys. Rev. D 96 (2017), no. 12, 123527
[arXiv:
1709.07865
[astro-ph.CO]].
[12]
Does the detection of primordial gravitational
waves exclude low energy inflation?
T. Fujita, R. Namba and Y. Tada
Phys. Lett. B 778 (2018), 17
[arXiv:
1705.01533
[astro-ph.CO]].
[11]
Inflationary Primordial Black Holes as All Dark Matter
K. Inomata, M. Kawasaki, K. Mukaida, Y. Tada and T. T. Yanagida
Phys. Rev. D 96 (2017), no. 4, 043504
[arXiv:
1701.02544
[astro-ph.CO]].
[10]
Inflationary primordial black holes for the LIGO gravitational wave events
and pulsar timing array experiments
K. Inomata, M. Kawasaki, K. Mukaida, Y. Tada and T. T. Yanagida
Phys. Rev. D 95 (2017), no. 12, 123510
[arXiv:
1611.06130
[astro-ph.CO]].
[9]
Squeezed Bispectrum in the $\delta N$ Formalism: Local Observer Effect in Field Space
Y. Tada and V. Vennin
JCAP 1702 (2017), no. 02, 021
[arXiv:
1609.08876
[astro-ph.CO]].
[8]
Primordial black holes as dark matter in supergravity inflation models
M. Kawasaki, A. Kusenko, Y. Tada and T. T. Yanagida
Phys. Rev. D 94 (2016), no. 8, 083523
[arXiv:
1606.07631
[astro-ph.CO]].
[7]
Revisiting constraints on small scale perturbations
from big-bang nucleosynthesis
K. Inomata, M. Kawasaki and Y. Tada
Phys. Rev. D 94 (2016), no. 4, 043527
[arXiv:
1605.04646
[astro-ph.CO]].
[6]
Can massive primordial black holes be produced
in mild waterfall hybrid inflation?
M. Kawasaki and Y. Tada
JCAP 1608 (2016), no. 08, 041
[arXiv:
1512.03515
[astro-ph.CO]].
[5]
Consistent generation of magnetic fields in axion
inflation models
T. Fujita, R. Namba, Y. Tada, N. Takeda and H. Tashiro
JCAP 1505 (2015), no. 05, 054
[arXiv:
1503.05802
[astro-ph.CO]].
[4]
Primordial black holes as biased tracers
Y. Tada and S. Yokoyama
Phys. Rev. D 91 (2015), 123534
[arXiv:
1502.01124
[astro-ph.CO]].
[3]
Anisotropic CMB distortions from non-Gaussian
isocurvature perturbations
A. Ota, T. Sekiguchi, Y. Tada and S. Yokoyama
JCAP 1503 (2015), no. 03, 013
[arXiv:
1412.4517
[astro-ph.CO]].
[2]
Non-perturbative approach for curvature perturbations
in stochastic-$\delta N$ formalism
T. Fujita, M. Kawasaki and Y. Tada
JCAP 1410 (2014), no. 10, 030
[arXiv:
1405.2187
[astro-ph.CO]].
[1]
A new algorithm for calculating the curvature perturbations
in stochastic inflation
T. Fujita, M. Kawasaki, Y. Tada and T. Takesako
JCAP 1312 (2013), 036
[arXiv:
1308.4754
[astro-ph.CO]].
Department of Physics, The University of Tokyo,
Bunkyo-ku, Tokyo 113-0033, Japan
Kavli Institute for the Physics and
Mathematics of the Universe (WPI), UTIAS,
The University of Tokyo, 5-1-5 Kashiwanoha,
Kashiwa, Chiba 277-8583, Japan
Institute for Cosmic Ray Research,
The University of Tokyo, 5-1-5 Kashiwanoha,
Kashiwa, Chiba 277-8582, Japan
Referees | |
---|---|
Dr. Masahiro Kawasaki | Supervisor |
Dr. Hitoshi Murayama | Supervisor |
Dr. Koichi Hamaguchi | Chief Examiner |
Dr. Aya Bamba | Examiner |
Dr. Masahiro Ibe | Examiner |
Dr. Shinji Miyoki | Examiner |
Dr. Jun’ichi Yokoyama | Examiner |
Department of Physics, The University of Tokyo,
Bunkyo-ku, Tokyo 113-0033, Japan
Kavli Institute for the Physics and
Mathematics of the Universe (WPI), UTIAS,
The University of Tokyo, 5-1-5 Kashiwanoha,
Kashiwa, Chiba 277-8583, Japan
Referees | |
---|---|
Dr. Masahiro Kawasaki | Supervisor |
Dr. Hitoshi Murayama | Supervisor |
Dr. Jun’ichi Yokoyama | Examiner |
Editor: Manuel Arca Sedda, Elisa Bortolas, Mario Spera
ISBN: 978-0-323-95636-9
Evolution of the inhomogeneous universe: From Inflation to structure formation
STOLAS: STOchastic LAttice Simulation of cosmic inflation ▼
We develop a C++ package of the STOchastic LAttice Simulation (STOLAS) of cosmic inflation. It performs the numerical lattice simulation in the application of the stochastic-deltaN formalism. STOLAS can directly compute the three-dimensional map of the observable curvature perturbation without estimating its statistical properties. In its application to two toy models of inflation, chaotic inflation and Starobinsky’s linear-potential inflation, we confirm that STOLAS is well-consistent with the standard perturbation theory. Furthermore, by introducing the importance sampling technique, we have success in numerically sampling the current abundance of primordial black holes in a non-perturbative way.
Y. Mizuguchi, T. Murata and Y. Tada
7th November 2024 @ KEK
oral, invited
Looping in the Primordial Universe
Cancellation of quantum corrections on the soft curvature perturbations ▼
We study the cancellation of quantum corrections on the superhorizon curvature perturbations from subhorizon physics beyond the single-clock inflation from the viewpoint of the cosmological soft theorem. As an example, we focus on the transient ultra-slow-roll inflation scenario and compute the one-loop quantum corrections to the power spectrum of curvature perturbations taking into account nontrivial surface terms in the action. We find that Maldacena's consistency relation is satisfied and guarantees the cancellation of contributions from the short-scale modes. As a corollary, primordial black hole production in single-field inflation scenarios is not excluded by perturbativity breakdown even for the sharp transition case in contrast to some recent claims in the literature. We also comment on the relation between the tadpole diagram in the in-in formalism and the shift of the elapsed time in the stochastic-δN formalism. We find our argument is not directly generalisable to the tensor perturbations.
Y. Tada, T. Terada, J. Tokuda
29th October 2024 @ CERN
oral, refereed
CAS-IBS CTPU-CGA-Tokyo Tech 2024 Workshop on Cosmology, Gravity, Particle Physics
Cancellation of quantum corrections on the soft curvature perturbations ▼
We study the cancellation of quantum corrections on the superhorizon curvature perturbations from subhorizon physics beyond the single-clock inflation from the viewpoint of the cosmological soft theorem. As an example, we focus on the transient ultra-slow-roll inflation scenario and compute the one-loop quantum corrections to the power spectrum of curvature perturbations taking into account nontrivial surface terms in the action. We find that Maldacena’s consistency relation is satisfied and guarantees the cancellation of contributions from the short-scale modes. As a corollary, primordial black hole production in single-field inflation scenarios is not excluded by perturbativity breakdown even for the sharp transition case in contrast to some recent claims in the literature. I may also comment on the relation between the tadpole diagram in the in-in formalism and the shift of the elapsed time in the stochastic-dN formalism as well as the application to the tensor perturbations. A recent lattice simulation in the stochastic formalism to sample PBHs may also be mentioned.
Y. Tada, T. Terada, J. Tokuda
17th October 2024 @ Kyukamura, Irago
invited talk
Dynamics of primordial black hole formation II
Cancellation of quantum corrections on the soft curvature perturbations
Y. Tada, T. Terada, J. Tokuda
7th October 2024 @ Nagoya U.
organiser
iTHEMS Cosmology Forum No.2
Scalar-induced gravitational waves as a cosmological phonograph ▼
Our universe has experienced phase transitions/crossovers several times throughout its thermal history.
The gravitational wave (GW) as a cosmological phonograph can record and tell us about such history thanks to its high penetration ability.
In particular, GWs sourced by oscillations of density contrasts called scalar-induced GWs (SIGWs), have sensitivity not only to the background expansion rate but also to the plasma sound speed and hence could serve more information on crossovers. Furthermore, they are closely related to the exotic astrophysical object: primordial black holes.
In this talk, the potential capabilities of SIGWs will be presented with a view to future observations.
Y. Tada
27th September 2024 @ iTHEMS
invited talk
Fourth Mini-workshop on the Early Universe
On the UV-completion and gravitational waves in the reheating of hybrid metric-Palatini Higgs inflation ▼
In this talk, I will give a brief review of the UV-completion of Higgs inflation with Starobinsky's R squared term and its generalisation to the Palatini gravity. Then, I would like to discuss the gravitational wave production in the reheating era as a physical expression of the UV-(in)completion depending on the theory of gravity.
M. He, T. Hiramatsu, Y. Mikura, Y. Tada
5th September 2024 @ Yatsugatake Commons
oral, refereed
Quintessential interpretation of the evolving dark energy in light of DESI ▼
The recent result of Dark Energy Spectroscopic Instrument (DESI) in combination with other cosmological data shows evidence of the evolving dark energy parameterized by w0waCDM model. We interpret this result in terms of a quintessential scalar field and demonstrate that it can explain the DESI result even though it becomes eventually phantom in the past. Relaxing the assumption on the functional form of the equation-of-state (EoS) parameter w = w(a), we also discuss a more realistic quintessential model. The implications of the DESI result for Swampland conjectures, cosmic birefringence, and the fate of the Universe are discussed as well.
S. Hayashi, H. Miyatake, Y. Tada, T. Terada
17th June 2024 @ UTokyo
invited talk
Joint workshop on General Relativity and Cosmology
Dive into the Cosmic Abyss: Echoes from Primordial Black Hole
Y. Tada
7th March 2024 @ Sunshine Shirako
invited talk
YITP long-term workshop "Gravity and Cosmology 2024"
Cancellation of quantum corrections on the soft curvature perturbations ▼
We study the cancellation of quantum corrections on the superhorizon curvature perturbations from subhorizon physics beyond the single-clock inflation from the viewpoint
of the cosmological soft theorem.
As an example, we focus on the transient ultra-slow-roll inflation scenario and compute the one-loop quantum corrections to the power spectrum of curvature perturbations taking into account nontrivial surface terms in the action.
We find that Maldacena’s consistency relation is satisfied and guarantees the cancellation of contributions from the short-scale modes.
As a corollary, primordial black hole production in single-field inflation scenarios is not excluded by perturbativity breakdown even for the sharp transition case in contrast to some recent claims in the literature.
I may also comment on the relation between the tadpole diagram in the in-in formalism and the shift of the elapsed time in the stochastic-δN formalism as well as the application to the tensor perturbations.
Y. Tada, T. Terada, J. Tokuda
29th January 2024 @ YITP
oral, refereed
The 32nd Texas Symposium on Relativistic Astrophysics
12th December 2023 @ Everbright International Hotel (Shanghai)
invited talk
KASHIWA DARK MATTER SYMPOSIUM 2023
5th December 2023 @ Kashiwa Library Media Hall
invited talk
JGRG 32
Cancellation of quantum corrections on the soft curvature perturbations ▼
We study the cancellation of quantum corrections on the superhorizon curvature perturbations from subhorizon physics beyond the single-clock inflation from the viewpoint
of the cosmological soft theorem.
As an example, we focus on the transient ultra-slow-roll inflation scenario and compute the one-loop quantum corrections to the power spectrum of curvature perturbations taking into account nontrivial surface terms in the action.
We find that Maldacena’s consistency relation is satisfied and guarantees the cancellation of contributions from the short-scale modes.
As a corollary, primordial black hole production in single-field inflation scenarios is not excluded by perturbativity breakdown even for the sharp transition case in contrast to some recent claims in the literature.
I may also comment on the relation between the tadpole diagram in the in-in formalism and the shift of the elapsed time in the stochastic-δN formalism as well as the application to the tensor perturbations.
Y. Tada, T. Terada, J. Tokuda
27th September 2023 @ Nagoya U.
oral, refereed
COSMO'23
Squeezed bispectrum and one-loop corrections in transient constant-roll inflation ▼
In canonical single-field inflation, the production of primordial black holes (PBH) requires a transient violation of the slow-roll condition.
The transient ultra slow-roll inflation is an example of such scenarios, and more generally, one can consider the transient constant-roll inflation.
We investigate the squeezed bispectrum in the transient constant-roll inflation and find that Maldacena's consistency relation holds for a sufficiently long-wavelength mode, whereas it is violated for modes around the peak scale for the non-attractor case.
We also demonstrate how the one-loop corrections are modified compared to the case of the transient ultra slow-roll inflation, focusing on representative one-loop terms originating from a time derivative of the second slow-roll parameter in the cubic action.
We find that the perturbativity requirement on those terms does not rule out the production of PBH from the transient constant-roll inflation.
Therefore, it is a simple counterexample of the recently claimed no-go theorem of PBH production from single-field inflation.
H. Motohashi, Y. Tada, T. Terada, J. Tokuda
15th September 2023 @ IFT
oral, refereed
YITP International Molecule-type Workshop
"Revisiting cosmological non-linearities in the era of precision surveys"
Stochastic approach to the inflationary universe ▼
The stochastic formalism known as an effective theory of superHubble coarse-grained fields is a powerful tool for a non-perturbative analysis of the inflationary universe. It views the coarse-grained inflaton field as a stochastic Brownian motion and its random behaviour leaves an imprint for the later universe as the primordial curvature perturbation. In this talk, I will first review the basic derivation of the stochastic formalism and then describe in detail the so-called stochastic-deltaN approach to calculate the curvature perturbation in the stochastic formalism. I will formulate the power spectrum and the probability density function of the coarse-grained curvature perturbation and show its numerical implementation. As practical examples, the hybrid-inflation and flat-inflection models are discussed, related to the recent hot topic: primordial black holes. I may mention its further application to gauge field production in axion inflation beyond the dynamics of the scalar inflaton fields, and also the lattice simulation in the stochastic formalism as a full numerical computation scheme.
Y. Tada
27th July 2023 @ YITP
oral, invited
New Horizons in Primordial Black Hole Physics
Statistics of coarse-grained cosmological fields in stochastic inflation ▼
We present a generic framework to compute the one-point statistics of cosmological perturbations, when coarse-grained at an arbitrary scale 𝑅, in the presence of quantum diffusion. Making use of the stochastic-𝛿𝑁 formalism, we show how it can be related to the statistics of the amount of expansion realised until the scale 𝑅 crosses out the Hubble radius. This leads us to explicit formulae for the probability density function (PDF) of the curvature perturbation, the comoving density contrast, and the compaction function. We then apply our formalism to the calculation of the mass distribution of primordial black holes produced in a single-field model containing a “quantum well” (i.e. an exactly flat region in the potential). We confirm that the PDFs feature heavy, exponential tails, with an additional cubic suppression in the case of the curvature perturbation. The large-mass end of the mass distribution is shown to be mostly driven by stochastic-contamination effects, which produce black holes more massive than those naively expected. This work bridges the final gap between the stochastic-inflation formalism and the calculation of the mass distribution of astrophysical objects such as primordial black holes and opens up various prospects that we finally discuss.
Y. Tada and V. Vennin
19th June 2023 @ Naples
oral, refereed
i-LINK workshop on observational cosmology
Y. Tada and M. Yamada
7th June 2023 @ Nagoya
oral, refereed
Domestic Molecule-type Workshop "Non-linear Nature of Cosmological Perturbations and its Observational Consequences"
On the soft theorem in the transient ultra-slow or constant roll inflation
H. Motohashi and Y. Tada
28th March 2023 @ YITP
oral, invited
19th Rencontres du Vietnam "Theory meeting experiments: particle astrophysics and cosmology"
Inflation theory — D'où venons-nous? Que sommes-nous? Où allons-nous? —
Y. Tada
8th January 2023 @ ICISE
oral, invited
TSQS 2022
Stochastic approach to cosmic inflation ▼
Cosmic inflation, the accelerated expansion phase of the universe in advance of the hot big-bang universe, is now considered as the standard paradigm of the modern cosmology. Not only does it realize a globally homogeneous and isotropic universe, but it can also generate fine density perturbations from the quantum zero-point fluctuation as a source of current cosmic structures like stars or galaxies. In the ordinary approach, the predicted fluctuation in each inflation model is calculated with use of the perturbative quantum field theory (QFT) in the curved spacetime. However, it cannot be applied for large fluctuations which can cause for example the so-called primordial black hole, one candidate of dark matter. Instead of the standard perturbative QFT, the effective theory of the coarse-grained field called stochastic formalism is also known as another powerful tool. In the accelerated expansion spacetime, the coarse-grained effective theory reads a classical (non-quantum), stochastic process (i.e., Brownian motion) and thus even large fluctuations can be treated directly. Since we have developed how to calculate fluctuations in a form conserved even after the end of inflation, many aspects of this approach have been investigated. I will introduce these recent developments in the talk.
Y. Tada
8th November 2022 @ The University of Tokyo
poster, refereed
JGRG31
Hybrid metric-Palatini Higgs inflation ▼
We propose an extension of the Higgs inflation to the hybrid metric-Palatini gravity, where we introduce non-minimal couplings between Higgs and both the metric-type Ricci scalar and the Palatini-type one. We find that slow-roll inflation can be realized in the large-field regime, giving the observationally favored predictions on the scalar spectral index, and the tensor-to-scalar ratio can take an arbitrary value depending on the non-minimal coupling parameters, the metric-one r ~ 10^-3 being the maximum. The UV cutoff as a low-energy EFT of this model is suppressed by the large non-minimal couplings between Higgs and Ricci scalars, but it can be lifted higher than the dynamical scale by introducing a new scalar degree of freedom, which is equivalent to embedding the curved scalar field space into a higher dimensional flat space. We however find that the Plack-scale UV-completion is realized only in the metric limit.
M. He, Y. Mikura, and Y. Tada
25th October 2022 @ The University of Tokyo
oral, refereed
Observational Cosmology Summer Workshop in 2022
Lattice simulation of stochastic inflation
Y. Tada
29th August 2022 @ The Ocean, HAMANAKO BENTEN RESORT & Maisaka cooperation center, Hamamatsu
oral, invited
FY2021 学術変革領域研究「ダークマター」シンポジウム
Primordial black holes and induced gravitational waves in light of the non-Gaussian tail ▼
The primordial black hole (PBH) is one of the candidate of dark matters if their masses are as small as asteroids. PBHs are likely to be accompanied by sizable stochastic gravitational waves (GWs) induced by the large primordial density perturbations which caused PBHs. As such GWs are expected detectable by future space-based GW telescopes such as LISA, it is important to precisely relate the GW power spectrum with the PBH mass function, which can be done by refining their prediction formulations from the common primordial density perturbations. Meanwhile, recently it has been pointed out that the inflaton's ultra-slow-roll dynamics, which is a promising mechanism to amplify the primordial perturbations, can significantly change the probability of large perturbations due to the so-called non-Gaussian (NG) tail and affect the PBH abundance prediction. In our works, we update the so-called peak theory for the PBH prediction in order to deal with the NG tail. We also discuss the effect of the NG tail on the induced GWs.
K. T. Abe, A. Escrivà, N. Kitajima, R. Inui, Y. Tada, S. Yokoyama, C. M. Yoo
30th March 2022 @ Kavli IPMU (online)
oral, invited
JGRG30
Probability density functions of coarse-grained curvature and density perturbations in
stochastic inflation ▼
The primordial black hole (PBH) has been attracting attentions more
and more. It is caused by the order-unity primordial perturbation and
thus its formation rate is evaluated by the probability density
function (PDF) of such a large perturbation, where the ordinary
perturbative calculation is expected to break down. In fact, the
stochastic formalism, a non-perturbative approach to inflation,
implies an even qualitative difference in the PDF behavior: the PDF at
large value decays only exponentially contrary to the Gaussian
suppression even in the case where the non-Gaussianity is small enough
around the origin. In order for the PBH mass function, the PDF of the
perturbation coarse-grained on an arbitrary scale corresponding to the
mass of interest. In this work, we formulate a non-perturbative
algorithm for the PDF of the coarse-grained curvature/density
perturbation, making use of the stochastic formalism.
Y. Tada and V. Vennin
9th December 2021 @ Waseda U. (online)
oral, refereed
The KEK-PH + KEK-Cosmo joint workshop on "Primordial Black Holes"
Primordial black holes in peak theory with a non-Gaussian tail ▼
In this work, we update the peak theory for the estimation of the primordial black hole (PBH) abundance,
particularly by implementing the critical behavior in the estimation of the PBH mass and employing the averaged compaction function for the PBH formation criterion to relax the profile dependence.
We apply our peak theory to a specific non-Gaussian feature called the exponential tail, which is characteristic in ultra slow-roll models of inflation. With this type of non-Gaussianity, the probability of a large perturbation is not suppressed by the Gaussian factor but decays only exponentially, so the PBH abundance is expected to be much enhanced.
Not only do we confirm this enhancement even compared to the case of the corresponding nonlinearity parameter fNL=5/2, but also we find that the resultant PBH mass spectrum has a characteristic maximal mass which is not seen in the simple Press--Schechter approach.
N. Kitajima, Y. Tada, S. Yokoyama and C. M. Yoo
19th October 2021 @ KEK (online)
oral, refereed
COSMO'21
Probability density functions of coarse-grained
curvature and density perturbations in
stochastic inflation ▼
The primordial black hole (PBH) has been attracting attentions more and more. It is caused by the order-unity primordial perturbation and thus its formation rate is evaluated by the probability density function (PDF) of such a large perturbation, where the ordinary perturbative calculation is expected to break down. In fact, the stochastic formalism, a non-perturbative approach to inflation, implies an even qualitative difference in the PDF behavior: the PDF at large value decays only exponentially contrary to the Gaussian suppression even in the case where the non-Gaussianity is small enough around the origin. In order for the PBH mass function, the PDF of the perturbation coarse-grained on an arbitrary scale corresponding to the mass of interest. In this work, we formulate a non-perturbative algorithm for the PDF of the coarse-grained curvature/density perturbation, making use of the stochastic formalism.
Y. Tada and V. Vennin
2–6th August 2021 @ The University of Illinois (online)
poster, refereed
2021 NRF-JSPS Workshop in particle physics, cosmology, and gravitation
Primordial black holes in peak theory with a non-Gaussian tail
N. Kitajima, Y. Tada, S. Yokoyama, and C-M. Yoo
21st July 2021 @ Alpensia Resort, Pyeongchang, Korea / online
oral, invited
Online JGRG Workshop 2020
Manifestly covariant theory of stochastic inflation ▼
The stochastic approach to inflation can non-perturbatively treat the superhorizon fluctuations
as the classical random noise to go beyond the standard perturbative QFT approach.
I first review how this approach enables us to calculate the observable curvature perturbations in a non-perturbative way
and how it can be implemented in a numerical program. I then describe the covariance of the stochastic theory
and the discretization scheme of the stochastic noise, which are important both theoretically and practically.
Mathematically the stochastic noise can be discretized in an arbitrary manner, but we reveal the physically motivated discretization,
which ensures the covariance of the stochastic theory on the inflatons' target manifold.
L. Pinol, S. Renaux-Petel, and Y. Tada
25th November 2020 @ online
poster, refereed
Outstanding Presentation Award Gold Prize
PBH & Stochastic inflation workshop
StocDeltaN: numerical approach to inflation in combination of the stochastic and delta N formalism ▼
The stochastic approach to inflation enables us to treat the superhorizon perturbations in a non-perturbative way.
Though it deals only with the inflatons’ perturbations in itself, fluctuations in the duration of inflation
can be connected with the observable curvature perturbations from the viewpoint of the delta N formalism.
In 2015, Vennin and Starobinsky revealed the adjoint Fokker-Planck equation for the probability density function of
such time fluctuations.
We with Renaux-Petel are now developing a C++ package to automatically solve this adjoint FP eq. and
enable a full stochastic analysis for arbitrary models of inflation.
I’ll introduce this ongoing project with several examples.
S. Renaux-Petel, Y. Tada, and V. Vennin
10th November 2020 @ online
oral, invited
The 14th International Conference on Gravitation, Astrophysics and Cosmology (ICGAC14)
Manifestly covariant theory of stochastic inflation ▼
The stochastic approach to inflation can non-perturbatively treat
the superhorizon fluctuations as the classical random noise to go beyond
the standard perturbative QFT approach. I first review how this approach enables us
to calculate the observable curvature perturbations in a non-perturbative way and
how it can be implemented in a numerical program. I then describe the covariance
of the stochastic theory and the discretization scheme of the stochastic noise,
which are important both theoretically and practically. Mathematically
the stochastic noise can be discretized in an arbitrary manner, but we reveal
the physically motivated discretization, which ensures the covariance of
the stochastic theory on the inflatons' target manifold.
L. Pinol, S. Renaux-Petel, Y. Tada, and V. Vennin
20th August 2020 @ National Central University, Taiwan (online)
oral, refereed
The 3rd KMI School:Machine Learning in Particle and
Astrophysics
StocDeltaN: numerical approach to inflation beyond the perturbation theory in the stochastic formalism ▼
The important role of inflation in the early universe is to generate the primordial perturbation as a source of current cosmic structures from the quantum zero-point fluctuation. The driving field, inflaton, gets fluctuated on the horizon scale and therefore each horizon patch behaves like as the Brownian motion, known as the stochastic formalism. The conserved perturbation inherited by the later universe is not the inflaton perturbation itself but the duration fluctuation of inflation. Therefore the problem is reduced to the probability distribution of the first passage time in a diffusion system. In principle, there is no need of the perturbative expansion in this approach, compared to the standard QFT calculation. We provide a C++ package "StocDeltaN", which automatically solve such a diffusion system and calculate the power spectrum of the primordial perturbation. It is applicable to general multi-scalar models beyond the slow-roll approximation.
S. Renaux-Petel, Y. Tada, and V. Vennin
6th March 2020 @ Nagoya U.
poster, refereed
POSTPONED
Focus Week on Primordial Black Holes
Primordial black hole tower: Dark matter, earth-mass, and LIGO black holes ▼
We investigate a possibility of primordial black hole (PBH) formation with a hierarchical
mass spectrum in multiple phases of inflation. As an example, we find that one can simultaneously realize a mass spectrum that has recently attracted a lot of attention: stellar-mass PBHs (~O(10)M_\odot) as a possible source of binary black holes detected by LIGO/Virgo collaboration, asteroid-mass (~O(10^-12)M_\odot) as a main component of dark matter, and earth-mass (~O(10^-5)M_\odot) as a source of ultrashort-timescale events in Optical Gravitational Lensing Experiment microlensing data. The recent refined de Sitter swampland conjecture may support such a multiphase inflationary scenario with hierarchical mass PBHs as a transition signal of each inflationary phase.
Y. Tada and S. Yokoyama
6th December 2019 @ KavliIPMU
oral, refereed
JGRG29
Stochastic inflation with an extremely large number of e-folds ▼
We propose a class of single-field, slow-roll inflation models in which a typical number of e-folds can be extremely large. The key point is to introduce a very shallow local minimum near the top of the potential in a hilltop inflation model. In particular, a typical number of e-folds is enhanced if classical behavior dominates around the local minimum such that the inflaton probability distribution is drifted to the local minimum as a whole. After the inflaton escapes from the local minimum due to the stochastic dynamics, the ordinary slow-roll inflation follows and it can generate the primordial density perturbation consistent with observation. Interestingly, our scenario inherits the advantages of the old and new inflation: the typical e-folds can be extremely large as in the old inflation, and slow-roll inflation naturally follows after the stochastic regime as in the new inflation. In our numerical example, the typical number of e-folds can be as large as 10^10^8, which is large enough for various light scalars such the QCD axion to reach the Bunch-Davies distribution.
N. Kitajima, Y. Tada, and F. Takahashi
27th November 2019 @ Kobe U.
oral, refereed
Theoretical aspects of non-Gaussianity from modern perspectives
Stochastic approach to non-Gaussianity
Y. Tada and V. Vennin
19th November 2019 @ YITP
oral, refereed
GWPAW 2019
Primordial black hole tower: Dark matter, earth-mass, and LIGO black holes
Y. Tada and S. Yokoyama
16th October 2019 @ Sanjo Kaikan, The University of Tokyo
oral, refereed
COSMO19
Primordial black hole tower: Dark matter, earth-mass, and LIGO black holes ▼
We investigate a possibility of primordial black hole (PBH) formation with a hierarchical mass spectrum in multiple phases of inflation. As an example, we find that one can simultaneously realize a mass spectrum which has recently attracted a lot of attention, stellar-mass PBHs ($\sim\mathcal{O}(10)M_\odot$) as a possible source of binary black holes detected by LIGO/VIRGO collaboration, asteroid-mass ($\sim\mathcal{O}(10^{-12})M_\odot$) as a main component of dark matter, and earth-mass ($\sim\mathcal{O}(10^{-15})M_\odot$) as a source of ultrashort-timescale events in OGLE microlensing data. The recent refined swampland conjecture may support these multi-phase inflationary scenario with hierarchical mass PBHs as a transition signal of each inflationary phase.
Y. Tada and S. Yokoyama
4th September 2019 @ RWTH Aachen U.
poster, refereed
15th Rencontres du Vietnam "COSMOLOGY"
Primordial black hole tower: Dark matter, earth-mass, and LIGO black holes ▼
As proposed by Hawking and Carr more than four decades ago, black holes can be formed even during the early radiation-dominated era in advance of the ordinary star formation, called “primordial black hole (PBH)”.
The possible mass of PBHs covers very wide range, and the extremely light one (~10^-12 M_\odot) attracts attention as a candidate of the main component of dark matters.
qMoreover recent LIGO/VIRGO’s gravitational wave detections have revealed the ubiquitous existence of slightly massive and less spinning BHs, which also can be explained by the primordial ones.
I first briefly review such astrophysical motivations of PBHs and current constraints on those.
Then I show that PBHs can be easily realized if inflation is not a single continuous phase but can be divided into multiple phases.
Interestingly recently proposed “dS conjecture” in the context of string theory may also support such a multi-phase inflation scenario.
Y. Tada and S. Yokoyama
16th August 2019 @ ICISE
oral, invited
3-day workshop: INFLATION AND GEOMETRY
Stochastic formalism and curvature perturbation ▼
In the stochastic formalism, perturbations on inflaton fields are absorbed into the background dynamics as Brownian noise, enabling the analysis beyond the perturbation theory. In this talk, I briefly review the so-called stochastic-deltaN approach, which combines the stochastic and deltaN formalisms to calculate the observable curvature perturbations in a non-perturbative way.
This approach can be described by the recursive set of partial differential equations, and therefore it can be numerically implemented as I will introduce. I also mention the extension this formalism to the non-trivial field space cases.
T. Fujita, L. Pinol, S. Renaux-Petel, Y. Tada, J. Tokuda,
and V. Vennin
13th June 2019 @ IAP
oral, invited
2-day mini-workshop: Axion Cosmology
PBH tower in multi-phase inflation ▼
Primordial black holes (PBH) have been attracting attentions again
in response to the LIGO's first direct detection of gravitational waves (GW)
from the merger of slightly more massive BHs $\sim\mathcal{O}(10)\,M_\odot$ than ordinary ones.
Also much lighter PBH $\sim\mathcal{O}(10^{20})\,\mathrm{g}$ can comprise all dark matters (DM)
and therefore the interesting mass ranges of PBH are separated.
On the other hand, the recent swampland conjecture suggests that the string theory might disfavor even the quasi-stable dS spacetime,
implying multiple phases of inflation. In this talk, we investigate the PBH formation
with multiple masses in such a multi-phase inflation model beyond the slow-roll approximation
on the second derivative of the inflatons' potential. We also discuss the secondary GW
induced by large density perturbations causing PBH.
Y. Tada and S. Yokoyama
15th May 2019 @ YITP
oral, refereed
Future Perspective in Cosmology and Gravity
PBH tower in multi-phase inflation ▼
Primordial black holes (PBH) have been attracting
attentions again in response to the LIGO's first direct
detection of gravitational waves (GW) from the merger of
slightly more massive BHs $\sim\mathcal{O}(10)\,M_\odot$
than ordinary ones. Also much lighter PBH
$\sim\mathcal{O}(10^{20})\,\mathrm{g}$ can comprise all
dark matters (DM) and therefore the interesting mass ranges
of PBH are separated. On the other hand, the recent
swampland conjecture suggests that the string theory might
disfavor even the quasi-stable dS spacetime, implying
multiple phases of inflation. In this talk, we investigate
the PBH formation with multiple masses in such a
multi-phase inflation model beyond the slow-roll
approximation on the second derivative of the inflatons'
potential. We also discuss the secondary GW induced by
large density perturbations causing PBH.
Y. Tada and S. Yokoyama
3rd April 2019 @ Nagoya U.
oral, refereed
Accelerating Universe in the Dark
PBH tower in multi-phase inflation ▼
Primordial black holes (PBH) have been attracting attentions
again in response to the LIGO's first direct detection of
gravitational waves (GW) from the merger of slightly more
massive BHs $\sim\mathcal{O}(10)\,M_\odot$ than ordinary
ones. Also much lighter PBH
$\sim\mathcal{O}(10^{20})\,\mathrm{g}$ can comprise all
dark matters (DM) and therefore the interesting mass
ranges of PBH are separated. On the other hand, the recent
swampland conjecture suggests that the string theory might
disfavor even the quasi-stable dS spacetime, implying
multiple phases of inflation. In this talk, we investigate
the PBH formation with multiple masses in such a
multi-phase inflation model beyond the slow-roll
approximation on the second derivative of the inflatons'
potential. We also discuss the secondary GW induced by
large density perturbations causing PBH.
Y. Tada and S. Yokoyama
7th March 2019 @ Kyoto U.
oral, refereed
FAPESP-JSPS Workshop on dark energy, dark matter,
and galaxies
Aspects of primordial black hole as dark matter
K. Inomata, M. Kawasaki, A. Kusenko, K. Mukaida, Y. Tada,
T. T. Yanagida, and S. Yokoyama
19th February 2019 @ U. of Sao Paulo
oral, refereed
Young Representative Speaker
JGRG28
Stochastic formalism and curvature perturbations ▼
After briefly reviewing our recent works about
the stochastic formalism extended to general
multi-field cases, we show several results of
our new numerical code. Combining the stochastic and
delta N formalism, it can automatically calculate the
statistics of e-folding numbers in the phase space for
general inflationary models and then obtain the power
spectrum of the curvature perturbations.
T. Fujita, L. Pinol, S. Renaux-Petel, Y. Tada,
and J. Tokuda
8th November 2018 @ Rikkyo U.
oral, refereed
MOGRA 2018
Stochastic inflation in a general field space ▼
Inflationary models in non-trivial field spaces encoded by
their non-canonical kinetic terms have attracted attentions recently.
We have then extended the so-called stochastic formalism
to such a general case.
This formalism investigates the fluctuation of inflatons
treating them as Brownian motions.
This work highlights the involved problem of this formalism,
related with the mathematical uncertainty of the definition
of noise integral.
Comparing the correlation functions in the stochastic formalism
and quantum field theory,
we clarify that this uncertainty cannot be removed
but rather the smallness of this would be a new criterion of
the validity for the application of this formalism.
We also check that it does not affect the observable curvature
perturbations so much at least in a single-field case.
Practical application prescriptions of this formalism may be
also mentioned.
T. Fujita, L. Pinol, S. Renaux-Petel, Y. Tada, and J. Tokuda
10th August 2018 @ Nagoya U.
oral, refereed
Fifteenth Marcel Grosmann Meeting
Stochastic inflation in a general field space ▼
Inflationary models in non-trivial field spaces encoded
by their non-canonical kinetic terms have attracted attentions recently.
On the other hand, the so-called stochastic formalism is known
as a powerful tool to investigate a quantum diffusion effect on inflation.
In this formalism, field fluctuations originating from
the quantum zero-point oscillation are mimicked by classical random noise.
We consistently formulate this prescription in a curved field space
with use of the path integral method including metric perturbations.
We also point out that this formalism has an inevitable ambiguity
related with the arbitrariness of noise integral
represented by the Ito or Stratonovich process.
The smallness of this ambiguity is suggested to be a novel criterion
of the validity of the application of this formalism.
T. Fujita, L. Pinol, S. Renaux-Petel, Y. Tada, and J. Tokuda
5th July 2018 @ University of Rome "La Sapienza"
oral, refereed
Infrared physics of gauge theories and quantum dynamics of inflation
Subtleties in stochastic formalism - Ito vs. Stratonovich ▼
The equation of motion for inflaton fields is given by
the Langevin equation in the stochastic formalism.
Mathematically there is an uncertainty in how to interpret
the noise integral like as the Ito or Stratonovich integral
in such a stochastic differential equation.
From the view point of the invariance of the multi-scalar Langevin
we derived under the field-space coordinate transformation,
we point out that there are drawbacks both in the Ito and
Stratonovich interpretations.
L. Pinol, S. Renaux-Petel, and Y. Tada
20th–21st January 2018 @ Biwako Club
oral, refereed
COSMO 17
Stochastic Formalism in Curved Field Space ▼
In multi-field inflation scenarios,
the scalar fields can span curved field spaces in general.
Recently it was pointed out that the sufficiently large field curvature
can make the entropic degrees of freedom tachyonic
during inflation and alter the inflation dynamics [PRL117, 141301].
This geometrical destabilization can be applied to
a large class of inflationary models.
To analyze the destabilization, we formalize the stochastic approach
in the general curved field space from first principles,
and also show some brief applications.
L. Pinol, S. Renaux-Petel, and Y. Tada
28th August–1st September 2017 @ the Universite Paris Diderot site, Amphitheatre Buffon
oral, refereed
Gordon Research Conference & Seminars "String Theory & Cosmology"
Primordial Black Hole, Dark Matter,
and Gravitational Wave ▼
The primordial black hole (PBH), which might be produced
due to possible large primordial perturbations,
has been recently refocused on more and more.
One of the main motivations of PBH is dark matter (DM),
although the latest observational constraints have almost
closed the possible window, except for ~10^{-13} solar-mass PBH.
Also the first direct detection of gravitational waves (GWs)
by LIGO/Virgo collaboration sheds light on the possibility that
the observed massive black holes might be primordial ones.
In my poster, I review these situations of PBH and
discuss the PBH formation in a novel double inflation model.
K. Inomata, M. Kawasaki, A. Kusenko, K. Mukaida, Y. Tada, and T. T. Yanagida
27th May–2nd June 2017 @ Renaissance Tuscany Il Ciocco, Lucca (Barga), Italy
poster, refereed
The 26th Workshop on General Relativity and Gravitation in Japan (JGRG26)
Squeezed Bispectrum in the delta N Formalism without Gauge Artifact
Y. Tada and V. Vennin
24th–28th October 2016 @ Osaka City University
oral, refereed
RESCEU Summer School
PBH Dark Matter in Supergravity Inflation Models
M. Kawasaki, A. Kusenko, Y. Tada, and T. T. Yanagida
24th–28th August 2016 @ Gifu
oral, not refereed
Second LeCosPA International Symposium
"Everything About Gravity"
Can massive primordial black holes be produced
in mild waterfall hybrid inflation?
M. Kawasaki and Y. Tada
14th–18th December 2015 @ NTU
oral, refereed
International Conference on Particle Physics and
Cosmology (COSMO-15)
PRIMORDIAL BLACK HOLES AS BIASED TRACERS
Y. Tada and S. Yokoyama
7th–11th September 2015 @ Warsaw
oral, refereed
International Conference on Particle Physics and Cosmology
(COSMO 2014)
Non-perturbative approach for curvature perturbations in
stochastic-delta N formalism
T. Fujita, M. Kawasaki, and Y. Tada
25th–29th August 2014 @ Chicago
poster, refereed
KEK Theory Meeting on Particle Physics Phenomenology
(KEK-PH2013 FALL)
A new algorithm for calculating the curvature perturbations
in stochastic inflation
T. Fujita, M. Kawasaki, Y. Tada, and T. Takesako
30th September–3rd October 2013 @ KEK
oral, refereed
第13回 観測的宇宙論ワークショップ
DESI による時間発展暗黒エネルギー観測のクインテッセンス解釈 ▼
DESI 観測の最近の結果は、他の宇宙論的データとの組み合わせにより、w0waCDM モデルによってパラメータ化された時間発展暗黒エネルギーの証拠を示している。我々はこの結果をスカラー場クインテッセンスの観点から解釈し、DESI 結果の素朴な延長はスカラー場が過去においてファントムエネルギーとなることを示す。状態方程式パラメータ w = w(a) の関数形の仮定を緩和し、より現実的なクインテッセンスモデルについても議論する。DESI の結果が沼地予想、宇宙の複屈折、宇宙の運命に与える影響についても議論する。
多田祐一郎, 寺田隆広
2024年9月25日 @ 金沢大
口頭, 査読あり
日本物理学会
DESI による時間発展暗黒エネルギー観測のクインテッセンス解釈 ▼
DESI 観測の最近の結果は、他の宇宙論的データとの組み合わせにより、w0waCDM モデルによってパラメータ化された時間発展暗黒エネルギーの証拠を示している。我々はこの結果をスカラー場クインテッセンスの観点から解釈し、DESI 結果の素朴な延長はスカラー場が過去においてファントムエネルギーとなることを示す。状態方程式パラメータ w = w(a) の関数形の仮定を緩和し、より現実的なクインテッセンスモデルについても議論する。DESI の結果が沼地予想、宇宙の複屈折、宇宙の運命に与える影響についても議論する。
多田祐一郎, 寺田隆広
2024年9月18日 @ 北海道大
口頭, 査読なし
"Physics meets Mathematics" Summary Workshop
インフレーションと超準解析 — 原始ブラックホールに向けて —
多田祐一郎
2024年2月10–12日 @ 明治元年創業びわ湖畔の料理旅館 恵美寿荘
主催
基研研究会 素粒子物理学の進展2023 (PPP2023)
原始ブラックホールは自然科学なのか
多田祐一郎
2023年9月1日 @ YITP
招待講演
日本物理学会春季大会
多重滝場ハイブリッドインフレーションと原始ブラックホール ▼
滝場が緩やかなハイブリッドインフレーションにおいて十分大きいスケールに大きな初期ゆらぎが作られ得るとして、重い原始ブラックホール (PBH) の実現が期待されたが、ゆらぎのスケールと振幅に単純な比例関係が成り立つことが明らかになり、重い PBH は必ず過剰生成されることが結論づけられた。一方滝場が1つではなく複数ある場合は滝場の数だけゆらぎが抑制されることが示唆されており、それにより適切な量の PBH を作る可能性は残されていた。本研究において我々はインフレーションの確率形式を用い初期ゆらぎを計算することで、確かにゆらぎが抑制されることを定量的に確認し、必要な滝場の数を明らかにする。
多田祐一郎, 山田將樹
2023年3月23日 @ オンライン
口頭, 査読なし
第35回 理論懇シンポジウム
原始ブラックホール研究の近年の進展 ▼
LIGO による重力波直接観測の成功以降、原始ブラックホール (BH) はますます注目を集めており、特に小惑星程度の原始 BH は暗黒物質の候補として盛んに研究されている。原始 BH が大きな初期ゆらぎに起因したならばそのようなゆらぎは同時に背景重力波も作り、近い将来 LISA 望遠鏡で検証できる。大きなゆらぎはインフレーション機構への示唆としても重要である。近年これらの関係性が集中的に研究されており、例えば数値シミュレーションおよびピーク理論の整備により初期ゆらぎの統計性から原始 BH 量の正確な予測が可能になってきている。一方で初期ゆらぎの確率分布が非常に重い裾を持つ可能性も指摘され、それによる重力波量の変更も議論されている。本発表ではこれらの近年の状況をまとめて紹介する。
多田祐一郎
2022年12月21–23日 @ 福島
ポスター, 査読あり
第11回観測的宇宙論ワークショップ
曲率ゆらぎへの非摂動的アプローチ ▼
曲率ゆらぎのガウス分布からのずれはインフレーション機構への重要な示唆であり、近年はさらに非摂動的な確率分布の裾も注目されている。本講演ではインフレーションの確率形式等を用いた曲率ゆらぎの統計性の非摂動解析をご紹介するとともに、インフレーション宇宙の3次元格子シミュレーションを提案する。これによりN体計算等の初期条件を第一原理的に与えられれば興味深い。
多田祐一郎
2022年12月13日 @ 国立天文台
招待講演
Workshop on Gravitation & Cosmology
Recent progress on stochastic inflation
多田祐一郎
2022年11月29日 @ 富山
集中講義
日本物理学会秋季大会
アクシオンインフレーションにおける U(1) ゲージ場の確率形式 ▼
本研究では擬スカラーインフラトンと結合する U(1) ゲージ場の確率形式を定式化する。物理的電磁場に対する確率微分方程式を導き、それらの解析解を与える。また数値シミュレーションによりハッブル長で平均化された電磁場が常にその方向を変えることを見る。これらは局所的に等方性が自発的破れを起こしていることを意味するが、各ハッブル領域は独立であると見なされ大局的な統計的等方性は保存されたままである。
藤田智弘, 向田享平, 多田祐一郎
2022年9月6日 @ 岡山理科大
口頭, 査読なし
日本物理学会第77回年次大会
原始ブラックホールのピーク理論と非ガウス尾 ▼
原始ブラックホール量の見積もり法としてピーク理論を用いた統計処理が注目されているが、我々はブラックホール質量の臨界挙動とブラックホール形成判定条件としての平均化コンパクション関数を導入するようピーク理論を更新した。またこの手法を用い、近年注目されている「指数尾」と呼ばれる非ガウス性を持った初期ゆらぎに対してのブラックホール質量関数を議論する。負の非線形パラメータを持つ非ガウスゆらぎに対するブラックホール形成判定条件の数値解析にも触れる。
A. Escrivà, 北嶋直弥, 多田祐一郎, 横山修一郎, 柳哲文
2022年3月17日 @ オンライン
口頭, 査読なし
DECIGO workshop
インフレーションの「現在」と重力波
多田祐一郎
2021年12月11日 @ オンライン
口頭, 招待
日本物理学会秋季大会
粗視化曲率ゆらぎの確率密度関数 ▼
インフレーションによる曲率ゆらぎについて、パワースペクトルやバイスペクトル等の小さなゆらぎに対する統計性は摂動論から良くわかっているが、原始ブラックホール等の文脈では大きなゆらぎの統計性を正確に知る必要がある。大きなゆらぎに対しては摂動論が破綻することが予想され、したがって非摂動的手法である確率形式を応用する研究が注目されている。素朴な確率形式では曲率ゆらぎの粗視化スケールはインフレーション終了時のホライズンサイズに固定されてしまうが、実際の運用では粗視化スケールを任意に取りたい。本講演ではいくつかの例とともに、任意粗視化スケールに対する曲率ゆらぎの確率密度関数の導出法を紹介する。
多田祐一郎 and V. Vennin
2021年9月14日 @ オンライン
口頭, 査読なし
日本物理学会第76回年次大会
インフレーションの確率形式に対する共変な定式化 ▼
通常インフレーションにおけるゆらぎに対しては摂動的量子場の計算が用いられるが、インフレーションの確率形式においては超ホライズンのゆらぎを古典乱数として非摂動的に扱うことができる。発表ではまずこの確率形式がインフレーション後の初期密度ゆらぎの計算にどのように役立つかを概観し、これを実装した数値計算プログラムについて簡単に紹介する。その後インフレーション確率形式の共変な定式化について議論する。数学的に確率過程は離散化を指定しないと一意に定まらないが、我々は物理的に好ましい離散化を明らかにし、インフラトン場の多様体上で確率運動方程式が共変になるよう確率インフレーションを定式化した。
L. Pinol, S. Renaux-Petel, 多田祐一郎
2021年3月13日 @ オンライン
口頭, 査読なし
日本物理学会秋季大会
Escape from the swamp with spectator ▼
近年弦理論の文脈で、ある種の低エネルギー有効理論がUV完全でない可能性を指摘する沼地予想が注目され、UV完全な有効理論が満たすべき様々な仮説的条件が提唱されている。これらはインフレーション機構にも制限を与え、典型的には長く続く加速膨張期を禁じる傾向がある。そこで我々は短いインフレーションが多数繰り返され合わせて必要な膨張量を達成する模型に着目し、これらが実際沼地仮説の条件を満たすことを示した。またこの模型のもと、大スケールでほぼスケール不変な初期ゆらぎをスペクテイター場によって実現し得ることも議論する。
小粥一寛, 多田祐一郎
2020年9月15日 @ 筑波大学 (オンライン)
口頭, 査読なし
日本物理学会第75回年次大会
極長ストカスティックインフレーション ▼
ヒルトップ型インフレーションに浅いポテンシャル極小点を導入することで極めて長いインフレーションを実現する可能性を議論する。極小点は十分浅く、ストカスティック効果により抜け出せ、その後観測宇宙を再現する通常のヒルトップインフレーションが続く。具体的には典型的に 10^{10^{10}} e-folds 程度のインフレーションが実現でき、例えば QCD axion が Bunch-Davies 分布に至るのに十分な長さである。
北嶋直弥, 多田祐一郎, 高橋史宜
2020年3月17日 @ 名古屋大学
口頭, 査読なし
日本物理学会秋季大会
多段階インフレーションによる原始ブラックホールタワー ▼
質量関数が階層的になるような原始ブラックホール (PBH) の形成を多段階インフレーションの文脈で議論する。
例として、LIGO/VIRGO 観測の重力波源となる$\mathcal{O}(10)M_\odot$ BH、暗黒物質を説明する$\mathcal{O}(10^{-12})M_\odot$ BH、
OGLE 重力レンズ現象のレンズ天体となり得る$\mathcal{O}(10^{-5})M_\odot$ BH がそれぞれ同時に実現されることを示した。最近提唱された dS 仮説もこうした多段階インフレーションシナリオを支持する。
多田祐一郎, 横山修一郎
2019年9月20日 @ 山形大学
口頭, 査読なし
第31回 理論懇シンポジウム
ストカスティックインフレーションと曲率ゆらぎ ▼
ストカスティック形式と delta N 形式を組み合わせることで
インフレーションでの曲率ゆらぎを計算するストカスティック-delta N 形式が提唱されているが、
それを実装することでほぼ自動的かつインフラトンの拡散効果も取り入れて
曲率ゆらぎのパワースペクトルを求める数値計算コードを紹介する。
藤田智弘, L. Pinol, S. Renaux-Petel, 多田祐一郎, 徳田順生
2018年12月19–21日 @ 京都大
ポスター, 査読なし
CANCELLED
日本物理学会秋季大会
ストカスティックインフレーションのノイズ処方について ▼
インフレーションにおける量子拡散の効果を調べるための
強力な処方としてストカスティック形式が知られている。
この形式では場の量子ゆらぎが古典的白色雑音で近似されるが、
この雑音の積分に関する不定性に付随して、
一般の複数場模型においてストカスティック形式には不可避な曖昧さが
存在することを指摘する。
また逆説的にこの曖昧さの小ささがストカスティック形式の
適用妥当性の新しい指標になることを提唱する。
藤田智弘, L. Pinol, S. Renaux-Petel, 多田祐一郎, 徳田順生
2018年9月14日 @ 信州大
口頭, 査読なし
日本物理学会秋季大会
曲がった場空間におけるストカスティック形式 ▼
スカラー場が複数存在するインフレーション模型において、
それらスカラー場は一般に曲がった場空間計量を張り得る。
この時場空間の曲率が十分に大きければ、
インフレーション中にエントロピー方向の自由度が
実効的にタキオニックになり得ることが指摘された(PRL. 117. 141301)。
我々はこの現象を解析するため、
曲がった場空間におけるストカスティック形式を作用から
第一原理に則って定式化する。
L. Pinol, S. Renaux-Petel, 多田祐一郎
2017年9月12–15日 @ 宇都宮大学
口頭, 査読なし
日本物理学会秋季大会
超重力ニューインフレーションにおける原始ブラックホール形成
川崎雅裕, A. Kusenko, 多田祐一郎, 柳田勉
2016年9月 @ 宮崎大学
口頭, 査読なし
松江素粒子物理学研究会
Can massive primordial black holes be produced
in mild waterfall hybrid inflation?
川崎雅裕, 多田祐一郎
2016年3月 @ 島根大学
口頭, 招待
日本物理学会秋季大会
超対称ハイブリッドインフレーションでの原始ブラックホール形成
川崎雅裕, 多田祐一郎
2015年9月 @ 大阪市立大学
口頭, 査読なし
日本物理学会第70回年次大会
バイアス効果による原始ブラックホール暗黒物質への制限
多田祐一郎, 横山修一郎
2015年3月 @ 早稲田大学
口頭, 査読なし
日本物理学会秋季大会
ストカスティック-δN形式による曲率ゆらぎへの非摂動的アプローチ
藤田智弘, 川崎雅裕, 多田祐一郎
2014年9月 @ 佐賀大学
口頭, 査読なし
日本物理学会秋季大会
ストカスティック効果を用いたインフレーションのゆらぎの解析
藤田智弘, 川崎雅裕, 多田祐一郎, 竹迫知博
2013年9月 @ 高知大学
口頭, 査読なし
— 星が先かブラックホールが先か &mdash
原始ブラックホール研究の最前線 ▼
私たちの天の川銀河や太陽系、ひいては私たち自身はどのように生まれてきたのでしょうか。
宇宙に銀河などの豊かな構造が作られるには、通常の物質に先んじて重力的に集まる「暗黒物質 (ダークマター)」という未知の物質が必要であることがわかっています。
この暗黒物質の正体として、かのホーキング博士が提唱した「原始ブラックホール」と呼ばれる特殊なブラックホールが注目されています。
特に現在の観測結果から許されるのはナノメートル程度のブラックホールであり、すなわち私たちの宇宙には実はナノサイズブラックホールが満ちているのかもしれません。
本講義ではこの原始ブラックホール仮説を通じて、関連する様々な宇宙の未解決問題、原始ブラックホール仮説をどう検証するか、さらには私たちの宇宙がどのように始まったかについて解説していきます。
多田祐一郎
2024年11月14日 @ 豊田西高校
招待講演
A Complete Guide to Primordial Black Holes ▼
Primordial black holes, the hypothetical black holes preceding the star-formation era, have been attracting attention more and more. In this talk, I'll review why they are fascinating, how we can realise and confirm/falsify them, what they can imply, and where should we go with them.
Y. Tada
27th May 2024 @ UTokyo
25th June 2024 @ BNU
Cancellation of quantum corrections on the soft curvature perturbations ▼
We study the cancellation of quantum corrections on the superhorizon curvature perturbations from subhorizon physics beyond the single-clock inflation from the viewpoint
of the cosmological soft theorem.
As an example, we focus on the transient ultra-slow-roll inflation scenario and compute the one-loop quantum corrections to the power spectrum of curvature perturbations taking into account nontrivial surface terms in the action.
We find that Maldacena’s consistency relation is satisfied and guarantees the cancellation of contributions from the short-scale modes.
As a corollary, primordial black hole production in single-field inflation scenarios is not excluded by perturbativity breakdown even for the sharp transition case in contrast to some recent claims in the literature.
I may also comment on the relation between the tadpole diagram in the in-in formalism and the shift of the elapsed time in the stochastic-δN formalism as well as the application to the tensor perturbations.
Y. Tada, T. Terada, J. Tokuda
21th February 2024 @ CERN
Cancellation of quantum corrections on the soft curvature perturbations ▼
We study the cancellation of quantum corrections on the superhorizon curvature perturbations from subhorizon physics beyond the single-clock inflation from the viewpoint of the cosmological soft theorem. As an example, we focus on the transient ultra-slow-roll inflation scenario and compute the one-loop quantum corrections to the power spectrum of curvature perturbations taking into account nontrivial surface terms in the action. We find that Maldacena's consistency relation is satisfied and guarantees the cancellation of contributions from the short-scale modes. As a corollary, primordial black hole production in single-field inflation scenarios is not excluded by perturbativity breakdown even for the sharp transition case in contrast to some recent claims in the literature. We also comment on the relation between the tadpole diagram in the in-in formalism and the shift of the elapsed time in the stochastic-δN formalism. We find our argument is not directly generalisable to the tensor perturbations.
Y. Tada, T. Terada, J. Tokuda,
22nd November 2023 @ ICG (online)
Nano-Hertz stochastic gravitational wave background ▼
The evidence of nano-Hertz stochastic gravitational wave (GW) background is reported by multiple pulsar timing array (PTA) collaborations. In this talk, I will review the basic idea of the PTA experiment and the astrophysical interpretation of such GW backgrounds.
Instead of the astrophysical interpretation, they can also be explained in several cosmological scenarios of the early universe.
Interestingly, the nano-Hertz range coincides with the Hubble scale during the cosmological quantum chromodynamics (QCD) phase transition.
The GW spectrum in cosmological scenarios can hence be affected by this phase transition.
Y. Tada
17th October 2023 @ E-lab, Nagoya U.
Stochastic approach to the inflationary universe ▼
The stochastic formalism known as an effective theory of superHubble coarse-grained fields is a powerful tool for a non-perturbative analysis of the inflationary universe. It views the coarse-grained inflaton field as a stochastic Brownian motion and its random behaviour leaves an imprint for the later universe as the primordial curvature perturbation.
In this talk, I will first review the basic derivation of the stochastic formalism and then describe in detail the so-called stochastic-deltaN approach to calculate the curvature perturbation in the stochastic formalism.
I will formulate the power spectrum and the probability density function of the coarse-grained curvature perturbation and show its numerical implementation.
As practical examples, the hybrid-inflation and flat-inflection models are discussed, related to the recent hot topic: primordial black holes.
I may mention its further application to gauge field production in axion inflation beyond the dynamics of the scalar inflaton fields.
Y. Tada
26th May 2023 @ CTP, invited
31st May 2023 @ IBS
13th June 2023 @ LMU
27th June 2023 @ LPENS
14th July 2023 @ Waseda
原始ブラックホールのピーク理論と非ガウス尾 ▼
宇宙初期にブラックホール (BH) が作られたとする「原始 BH 仮説」は近年ますます注目を集めている。
特に小惑星程度の質量 (~ 10^22 g) の原始 BH は暗黒物質の主要素の候補であるとともに、
原始 BH を作るために必要な大きな初期曲率ゆらぎが背景重力波を誘導しそれが LISA で検証し得るため、重要な可能性である。
一方そのような大きな曲率ゆらぎを作るインフレーション模型によっては (ultra slow-roll 模型など)、
曲率ゆらぎ ζ の分布が特に ζ ~ 1 の領域でガウス分布から大きくずれ得ることが指摘され、非ガウス尾と呼ばれている。
非ガウス尾は原始 BH 量には大きく影響する一方、背景重力波量にはあまり影響しないと予想されるため、
非ガウス尾の存在は「原始 BH 量 ↔︎ 背景重力波量」の対応を著しく変更する可能性がある。
そこで本講演ではピーク理論を用いて非ガウス尾の存在の下原始 BH 量を正確に見積もるとともに、
背景重力波への影響も摂動展開を用いて議論する。
多田祐一郎
2022年6月7日 @ 立教大, 招待
22nd March 2022 @ Nagoya U. (online), invited
名大発アカデミックフラッシュ 第2報
宇宙の「インフレ」と「金融工学」
多田祐一郎
2021年9月3日 @ オンライン, 招待
名古屋大学・名古屋市科学館 公開オンラインセミナー
星が先かブラックホールが先か?原始ブラックホール研究の最前線
多田祐一郎
2021年8月22日 @ オンライン, 招待
Self-introduction,
or a biased view of what theoretical cosmologists are recently interested in ▼
Recent progress in cosmological observations represented by Planck, LIGO, etc. has been changing the research “trend” of the early universe.
While Starobinsky’s minimal (but somewhat “weird”) inflationary scenario is favored, the primordial black hole (PBH) as a consequence of exotic inflation has been also motivated more and more.
Through a brief review of these situations, I will self-introduce my research topics such as stochastic calculus approach to inflationary perturbations, multistage inflation for PBH production, metric-affine gravity as a new interpretation of Starobinsky’s model, and so on.
Y. Tada
25th May 2021 @ E-lab, Nagoya U. (online), invited
インフレーションの確率形式に対する共変な定式化 ▼
通常インフレーションにおけるゆらぎに対しては摂動的量子場の計算が用いられるが、
インフレーションの確率形式においては超ホライズンのゆらぎを古典乱数として非摂動的に扱うことができる。
発表ではまずこの確率形式がインフレーション後の初期密度ゆらぎの計算にどのように役立つかを概観し、
これを実装した数値計算プログラムについて簡単に紹介する。
その後インフレーション確率形式の共変な定式化について議論する。
数学的に確率過程は離散化を指定しないと一意に定まらないが、
我々は物理的に好ましい離散化を明らかにし、
インフラトン場の多様体上で確率運動方程式が共変になるよう確率インフレーションを定式化した。
L. Pinol, S. Renaux-Petel, 多田祐一郎, V. Vennin
2020年11月12日 @ 駒場素粒子研, 東大 (online), 招待
Manifestly covariant theory of stochastic inflation ▼
The stochastic approach to inflation can non-perturbatively treat the superhorizon fluctuations
as the classical random noise to go beyond the standard perturbative QFT approach.
I first review how this approach enables us to calculate the observable curvature perturbations in a non-perturbative way
and how it can be implemented in a numerical program. I then describe the covariance of the stochastic theory
and the discretization scheme of the stochastic noise, which are important both theoretically and practically.
Mathematically the stochastic noise can be discretized in an arbitrary manner, but we reveal the physically motivated discretization,
which ensures the covariance of the stochastic theory on the inflatons' target manifold.
L. Pinol, S. Renaux-Petel, Y. Tada, and V. Vennin
11th November 2020 @ Padova (online)
JGRG Webinar Series
A manifestly covariant theory of multifield stochastic inflation in phase space ▼
Stochastic inflation is an effective theory describing the super-Hubble,
coarse-grained, scalar fields driving inflation, by a set of Langevin equations.
We previously highlighted the difficulty of deriving a theory of stochastic inflation
that is invariant under field redefinitions, and the link with the ambiguity of
discretisation schemes defining stochastic differential equations. In this paper,
we solve the issue of these "inflationary stochastic anomalies" by using the
Stratonovich discretisation satisfying general covariance, and identifying
that the quantum nature of the fluctuating fields entails the existence of
a preferred frame defining independent stochastic noises. Moreover,
we derive physically equivalent Ito-Langevin equations that are manifestly
covariant and well suited for numerical computations. These equations are
formulated in the general context of multifield inflation with curved field space,
taking into account the coupling to gravity as well as the full phase space in
the Hamiltonian language, but this resolution is also relevant in simpler
single-field setups. We also develop a path-integral derivation of these equations,
which solves conceptual issues of the heuristic approach made at the level of
the classical equations of motion, and allows in principle to compute corrections to
the stochastic formalism. Using the Schwinger-Keldysh formalism, we integrate out
small-scale fluctuations, derive the influence action that describes their effects
on the coarse-grained fields, and show how the resulting coarse-grained effective
Hamiltonian action can be interpreted to derive Langevin equations with manifestly
real noises. Although the corresponding dynamics is not rigorously Markovian,
we show the covariant, phase-space Fokker-Planck equation for the
Probability Density Function of fields and momenta when the Markovian approximation
is relevant, and we give analytical approximations for the noises’ amplitudes
in multifield scenarios.
L. Pinol, S. Renaux-Petel, and Y. Tada
22nd October 2020 @ online, invited
Manifestly covariant theory of stochastic inflation ▼
The stochastic approach to inflation can non-perturbatively treat the superhorizon fluctuations as the classical random noise to go beyond the standard perturbative QFT approach. I first review how this approach enables us to calculate the observable curvature perturbations in a non-perturbative way and how it can be implemented in a numerical program. I then describe the covariance of the stochastic theory and the discretization scheme of the stochastic noise, which are important both theoretically and practically. Mathematically the stochastic noise can be discretized in an arbitrary manner, but we reveal the physically motivated discretization, which ensures the covariance of the stochastic theory on the inflatons' target manifold.
L. Pinol, S. Renaux-Petel, Y. Tada, and V. Vennin
20th October 2020 @ KEK (online)
Manifestly covariant theory of stochastic inflation ▼
The stochastic approach to inflation can non-perturbatively treat the superhorizon fluctuations as the classical random noise to go beyond the standard perturbative QFT approach. I first review how this approach enables us to calculate the observable curvature perturbations in a non-perturbative way and how it can be implemented in a numerical program. I then describe the covariance of the stochastic theory and the discretization scheme of the stochastic noise, which are important both theoretically and practically. Mathematically the stochastic noise can be discretized in an arbitrary manner, but we reveal the physically motivated discretization, which ensures the covariance of the stochastic theory on the inflatons' target manifold.
L. Pinol, S. Renaux-Petel, Y. Tada, and V. Vennin
7th October 2020 @ IBS (online), invited
Aspects of primordial black holes and
implication to multi-phase inflation ▼
As proposed by Hawking and Carr more than four decades ago, black holes can be formed even during the early radiation-dominated era in advance of the ordinary star formation, called “primordial black hole (PBH)”.
The possible mass of PBHs covers very wide range, and the extremely light one (~10^-12 M_\odot) attracts attention as a candidate of the main component of dark matters.
Moreover recent LIGO/VIRGO’s gravitational wave detections have revealed the ubiquitous existence of slightly massive and less spinning BHs, which also can be explained by the primordial ones.
I first briefly review such astrophysical motivations of PBHs and current constraints on those.
Then I show that PBHs can be easily realized if inflation is not a single continuous phase but can be divided into multiple phases.
Interestingly recently proposed “dS conjecture” in the context of string theory may also support such a multi-phase inflation scenario.
K. Inomata, M. Kawasaki, A. Kusenko, K. Mukaida, Y. Tada, T. T. Yanagida, and S. Yokoyama
7th June 2019 @ IRAP
Aspects of primordial black holes and
implication to multi-phase inflation ▼
As proposed by Hawking and Carr more than four decades ago, black holes can be formed even during the early radiation-dominated era in advance of the ordinary star formation, called “primordial black hole (PBH)”.
The possible mass of PBHs covers very wide range, and the extremely light one (~10^-12 M_\odot) attracts attention as a candidate of the main component of dark matters.
Moreover recent LIGO/VIRGO’s gravitational wave detections have revealed the ubiquitous existence of slightly massive and less spinning BHs, which also can be explained by the primordial ones.
I first briefly review such astrophysical motivations of PBHs and current constraints on those.
Then I show that PBHs can be easily realized if inflation is not a single continuous phase but can be divided into multiple phases.
Interestingly recently proposed “dS conjecture” in the context of string theory may also support such a multi-phase inflation scenario.
K. Inomata, M. Kawasaki, A. Kusenko, K. Mukaida, Y. Tada, T. T. Yanagida, and S. Yokoyama
23rd May 2019 @ Tohoku U., invited
一般的場空間におけるストカスティックインフレーション ▼
インフレーションにおける重要な観測量の1つとして
量子振動由来のスカラーゆらぎが知られていますが、
このゆらぎを含めたインフレーションの解析手法として
ストカスティックインフレーションという形式があります。
この形式ではスカラーゆらぎを古典的白色ノイズで近似しますが、
我々は白色ノイズの数学的定義の任意性に起因して、
ストカスティック形式に不可避な不定性が存在することを指摘し、
逆説的にこの不定性の小ささがストカスティック形式の
適用妥当性の新たな指標となることを提唱します。
またストカスティック形式の実用的な応用についてもご紹介します。
藤田智弘, L. Pinol, S. Renaux-Petel, 多田祐一郎, 徳田順生
2018年10月9日 @ 立教大学, 招待
Stochastic inflation in a general field space ▼
Inflationary models in non-trivial field spaces encoded by
their non-canonical kinetic terms have attracted attentions recently.
We have then extended the so-called stochastic formalism to
such a general case.
This formalism investigates the fluctuation of inflatons treating them
as Brownian motions.
This work highlights the involved problem of this formalism,
related with the mathematical uncertainty of the definition of
noise integral.
Comparing the correlation functions in the stochastic formalism and
quantum field theory, we clarify that this uncertainty cannot be removed
but rather the smallness of this would be a new criterion of
the validity for the application of this formalism.
We also check that it does not affect the observable curvature
perturbations so much at least in a single-field case.
Practical application prescriptions of this formalism may be
also mentioned.
T. Fujita, L. Pinol, S. Renaux-Petel, Y. Tada, and J. Tokuda
26th June 2018 @ APC
Stochastic Formalism in Curved Field Space ▼
In multi-field inflation scenarios, the scalar fields can span curved field spaces in general.
Recently it was pointed out that the sufficiently large field curvature can make the entropic degrees of freedom tachyonic during inflation and
alter the inflation dynamics [PRL117, 141301]. This geometrical destabilization can be applied to a large class of inflationary models.
To analyze the destabilization, we formalize the stochastic approach in the general curved field space from first principles.
Also I’ll briefly mention the slow-roll phase well after the geometrical destabilization.
L. Pinol, S. Renaux-Petel, and Y. Tada
4th September 2017 @ RESCEU
19th September 2017 @ Kobe U.
20th September 2017 @ Nagoya U.
Primordial Black Hole, Dark Matter, and LIGO's Gravitational Wave Event ▼
The primordial black hole (PBH), which might be produced due to possible large primordial perturbations,
has been recently refocused on more and more.
One of the main motivations of PBH is dark matter (DM),
although the latest observational constraints have almost closed the possible window, except for ~10^{-13} solar-mass PBH.
Also the first direct detection of gravitational waves (GWs) by LIGO/Virgo collaboration sheds light on the possibility
that the observed massive black holes might be primordial ones.
In my talk, I will review these situations of PBH and discuss the PBH formation in two classes of inflation;
hybrid and double inflation.
First I will briefly show that suitable PBHs can NOT be produced in hybrid inflation,
and then the possibilities for DM or LIGO’s event will be investigated in a novel double inflation model.
K. Inomata, M. Kawasaki, A. Kusenko, K. Mukaida,
Y. Tada, and T. T. Yanagida
20th April 2017 @ IAP
Primordial Black Hole, Dark Matter, and LIGO's Gravitational Wave Event
K. Inomata, M. Kawasaki, A. Kusenko, K. Mukaida,
Y. Tada, and T. T. Yanagida
16th December 2016 @ Waseda U., invited
Stochastic-delta N formalism and massive
primordial black hole formation in hybrid inflation
M. Kawasaki and Y. Tada
22nd June 2016 @ ICG, University of Portsmouth
Stochastic-delta N formalism and massive
primordial black hole formation in hybrid inflation
M. Kawasaki and Y. Tada
20th June 2016 @ University of Sussex
CANCELLED
Stochastic-delta N formalism and massive primordial
black holes in hybrid inflation
M. Kawasaki and Y. Tada
18th April 2016 @ UT hep-th, invited
Stochastic-delta N formalism and massive primordial black holes
in hybrid inflation
M. Kawasaki and Y. Tada
29th March 2016 @ Kyoto
Can massive primordial black holes be produced
in mild waterfall hybrid inflation?
M. Kawasaki and Y. Tada
29th February 2016 @ RESCEU, invited
Stochastic-delta N formalism and massive primordial
black holes in hybrid inflation
M. Kawasaki and Y. Tada
27th January 2016 @ KEK
Stochastic-deltaN formalism and primordial black holes
in hybrid inflation
M. Kawasaki and Y. Tada
14th–18th & 21st September 2015 @ Padova & IAP
バイアストレーサーとしての原始ブラックホール
多田祐一郎, 横山修一郎
2015年6月25日 @ 名古屋大学 Cセミナー
Joint seminar of gravity and cosmology
Primordial black holes as biased tracers
Y. Tada and S. Yokoyama
16th February 2015 @ IPMU
materials
Stochastic-δN formalism
T. Fujita, M. Kawasaki, Y. Tada, and T. Takesako
19th–24th August 2014 @ Helsinki U.
Prof. Kari Enqvist's group, University of Helsinki
•
1st October–22nd December 2014
ALPS course work
Classical and Quantum Gravity (CQG)
European Physical Journal C (EPJC)
Journal of Cosmology and Astroparticle Physics (JCAP)
Monthly Notices of the Royal Astronomical Society (MNRAS)
Modern Physics Letters A (MPLA)
Physical Review D (PRD)
Physical Review Letters (PRL)
Progress of Theoretical and Experimental Physics (PTEP)
Universe
Physics meets Mathematics
(PI)
International Research Network Extragalactic astrophysics and Cosmology (NECO)
理論天文学宇宙物理学懇談会
日本物理学会
"Physics meets Mathematics" まとめ合宿
•
10–12th February 2024
JGRG 32
•
27th November–1st December 2023
名大発アカデミックフラッシュ 第2報
宇宙の「インフレ」と「金融工学」
多田祐一郎
2021年9月3日 @ オンライン, 招待
名古屋大学・名古屋市科学館 公開オンラインセミナー
星が先かブラックホールが先か?原始ブラックホール研究の最前線
多田祐一郎
2021年8月22日 @ オンライン, 招待
Inflationary stochastic anomalies
L. Pinol, S. Renaux-Petel and Y. Tada
Class. Quant. Grav. 36, no. 7, 07LT01 (2019)
[arXiv:
1806.10126
[gr-qc]].
Conformal inflation in the metric-affine geometry
Y. Mikura, Y. Tada and S. Yokoyama
EPL 132, no.3, 39001 (2020)
[arXiv:
2008.00628
[hep-th]].
Online JGRG Workshop 2020
•
27th November 2020
Manifestly covariant theory of stochastic inflation (poster) ▼
The stochastic approach to inflation can non-perturbatively treat the superhorizon fluctuations
as the classical random noise to go beyond the standard perturbative QFT approach.
I first review how this approach enables us to calculate the observable curvature perturbations in a non-perturbative way
and how it can be implemented in a numerical program. I then describe the covariance of the stochastic theory
and the discretization scheme of the stochastic noise, which are important both theoretically and practically.
Mathematically the stochastic noise can be discretized in an arbitrary manner, but we reveal the physically motivated discretization,
which ensures the covariance of the stochastic theory on the inflatons' target manifold.
L. Pinol, S. Renaux-Petel, and Y. Tada
FAPESP-JSPS Workshop on dark energy, dark matter, and galaxies
•
February 2019
Aspects of primordial black hole as dark matter (oral)
K. Inomata, M. Kawasaki, A. Kusenko, K. Mukaida, Y. Tada,
T. T. Yanagida, and S. Yokoyama
ICRR Master and Doctor Thesis Workshop • 24th February 2017
天文・天体物理若手夏の学校 • 2015年7月30日
天文・天体物理若手夏の学校 • 2013年8月1日
JSPS Grant-in-Aid for Scientific Research (C)
•
1st April 2024–31st March 2027
No. 24K07047, Principal Investigator, ¥4,550,000.
2023 Collaborative Research Grants for YLC
•
1st July 2023–31st March 2024
Principal Investigator, ¥1,000,000.
JSPS Grant-in-Aid for Early-Career Scientists
•
1st April 2021–31st March 2024
No. 21K13918, Principal Investigator, ¥4,680,000.
JSPS Grant-in-Aid for Early-Career Scientists
•
1st April 2019–31st March 2022
No. 19K14707, Principal Investigator, ¥1,560,000.
Grant-in-Aid for JSPS Fellows
•
25th April 2018–31st March 2021
No. 18J01992, JSPS Fellow (PD), ¥3,640,000.
Grant-in-Aid for JSPS Fellows
•
24th April 2015–31st March 2017
No. 15J10829, JSPS Fellow (DC2), ¥1,900,000.
Yuichiro Tada
ES bldg. 604, Nagoya University
Furocho Chikusaku Nagoya
Aichi 464-8602 Japan
+81 (0)80-9566-9181
yuichiro.t.tada@gmail.com
tada.yuichiro.y8@f.mail.nagoya-u.ac.jp
tada.yuichiro@e.mbox.nagoya-u.ac.jp
tada_at_iap.fr
yuichiro.tada_at_ipmu.jp