2020/7/20 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報

Soichiro Hashiba

2020/7/13 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報

Ido Ben-Dayan

2020/7/6 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報

Introduction of peak statistics of Gaussian random fields

Minxi He

In this talk, the statistical theory of peaks of Gaussian random fields
are introduced, based on Bardeen, Bond, Kaiser, and Szalay (1986) which
is usually called BBKS or peak theory. This theory is originally used
to study the statistical properties of the structure formation in the
Universe. Recently, this theory is applied to the study of primordial
black holes.
References:
Bardeen, Bond, Kaiser, Szalay, Astrophys. J. 304, 15 (1986)
Young, Byrnes, Sasaki (2014)
Yoo, Harada, Garriga, Kohri, 1805.03946
Germani, Musco, Phys. Rev. Lett. 122, no. 14, 141302 (2019)
Suyama, Yokoyama, 1912.04687
Wu, 2005.00441
Tokeshi, Inomata, Yokoyama, 2005.07153

2020/6/29 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報

From scattering amplitudes to binary system

Hiroaki Tahara

I will briefly introduce a few recent letters which calculate classical Hamiltonian for compact spinless binaries up to third post-Minkowskian order with modern tools for scattering amplitudes.

[1] C. Cheung, et al., “From scattering amplitudes to classical potentials in the post-Minkowskian expansion,” PRL 121, no.25, 251101 (2018) [arXiv:1808.02489 [hep-th]].
[2] Z. Bern, et al., “Scattering amplitudes and the conservative Hamiltonian for binary systems at third post-Minkowskian order,” PRL 122, no.20, 201603 (2019) [arXiv:1901.04424 [hep-th]].
[3] Z. Bern, et al., “Black Hole Binary Dynamics from the Double Copy and Effective Theory,” JHEP 10, 206 (2019) [arXiv:1908.01493 [hep-th]]

2020/6/22 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報

Experiments towards the Quantum Nature of Gravity and the Related Theoretical Challenges

Tomohiro Fujita

Quantum gravity is one of the most outstanding problems in physics. In fact, we do not know if
gravity should be quantized in a similar way to the other degree of freedoms. Recently, a couple
of experiments are proposed to test whether gravitational fields become quantum superposition or not.
After the proposal, a number of questions are raised and the possible implications of the experiments
are under discussion. I will introduce the proposed experiments and the related questions
and hope to specify the remaining theoretical challenges to clarify the implications.

References:
[1] Phys.Rev.Lett. 119 (2017) 24, 240401 [1707.06050]
[2] Phys.Rev.Lett. 119 (2017) 24, 240402 [1707.06036]
[3] Phys.Lett.B 792 (2019) 64-68 [1808.05842]
[4] arXiv: 2005.14596

2020/6/15 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報

de Sitter wave function and Euclidean AdS

Yusuke Yamada

In cosmology, correlation functions are important observables. One can evaluate them e.g. within the in-in perturbation formalism or using wave functional(=path integral). The wave functional/path integral approach manifests the relation to the path integral in Euclidean AdS.
In this talk, I will review the relation between dS and EAdS path integral and discuss the subtlety of their relation. As I will show, the Bunch-Davies wave functional can be given by the analytic continuation of EAdS path integral, which can be evaluated by the technique used in AdS/CFT context.
Independently of the main topic, I will also review vacuum states in de Sitter QFT, if time allows. (It is unlikely, though. )

References
[1] D. Harlow, D. Stanford, arXiv:1104.2621
[2] D. Anninos, T. Anous, D. Z. Freedman, G. Konstantinidis, JCAP11(2015)048
[3] J. Maldacena, JHEP0305(2003)013
…etc.

2020/6/8 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報

Cosmological superfluids and phonons

Kohei Kamada

Spontaneous space-time symmetry breaking is now known to be a key to explore cosmology
such as inflation, dark energy, and dark matter.
In this talk, I will introduce the way to understand the cosmological perturbation
as the Nambu-Goldstone mode of the space-time symmetry breaking
and to construct their effective field theory, following the references [1,2].
I start from the brief introduction of the coset construction and inverse Higgs constraints,
Then I discuss the way to understand the perturbation to be the phonons in superfluids,
which is related to e.g., DBI and cuscuton
and construct their effective Lagrangian.
If time allows, I will also discuss the appearance of other (unconventional) types of phonons.

References
[1] Enrico Pajer, David Stefanyszyn, "Symmetric Superfluids", arXiv:1812.05133
[2] Tanguy Grall, Sadra Jazayeri, David Stefanyszyn, "The Cosmological Phonon: Symmetries and Amplitudes on Sub-Horizon Scales”, arXiv:2005.12937
[3] Sidney R. Coleman, J. Wess, Bruno Zumino, “Structure of phenomenological Lagrangians. 1“, Phys.Rev. 177 (1969) 2239-2247
[4] Curtis G. Jr. Callan, Sidney R. Coleman, J. Wess, Bruno Zumino, “Structure of phenomenological Lagrangians. 1“, Phys.Rev. 177 (1969) 2247-2250
[5] E.A. Ivanov, V.I. Ogievetsky, "The Inverse Higgs Phenomenon in Nonlinear Realizations”, Teor.Mat.Fiz. 25 (1975) 164-177,
[6] D.T. Son, “Low-energy quantum effective action for relativistic superfluids”, hep-ph/0204199

2020/6/1 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報

Stochastic dynamics from Quantum mechanics

Jun'ichi Yokoyama

I will introduce several very old papers to extract
stochastic dynamics from quantum mechanics starting
from the Schroedinger equation, with a wish to apply
for quantum tunneling in real time. I will not go into
field theory, though.

References (chronological order)
E. Nelson "Derivation of Schroedinger equation from Newtonian mechanics"
Physical Review 150(1966)1079
F Guerra and P Ruggiero "New interpretation of the Euclidean-Markov
field in the
frame work of physical Minkowski spacetime" Physical Review Letters
31(1973)1022
K. Yasue "Detailed time dependent description of tunneling phenomena
arising from stochastic quantization" Physical Review Letters 40(1978)665
D.L. Weaver "Tunneling, stochastic quantization, and escape over a barrier"
Physical Review Letters 23(1978)1473
F. Guerra "Structural aspects of stochastic mechanics and stochastic
field theory"
Physics Reports 77(1981)263

2020/5/25 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報

Quantum entanglement in the early Universe

Kouki Tokeshi

The quantum state becomes squeezed after inflation due to cosmological perturbations, and hence there exists quantum entanglement. In this talk, we start with the simplest example which shows quantum entanglement, and see the relation between Hawking temperature of a BH and the entangled particle pair near the horizon, in the viewpoint of themo field dynamics (TFD). After these examples, we consider the quantum squeezed state after inflation, and from the result we finally draw some implications on PBHs.

Refs.
[1] A. Albrecht et al., PRD 50 (1994) 4807 [astro-ph/9303001]
[2] T. Prokopec, Class. Quantum Grav. 10 (1993) 2295-2306
[3] M. Hashizume and M. Suzuki, Physica A 392 (2013) 3518-3530 [cond-mat/1305.4679]
[4] L. Espinosa-Portalés and J. García-Bellido, PRD 101 (2020) 043514 [gr-qc/1907.07601]

2020/5/18 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報

Inhomogeneous nucleosynthesis

Fumio Uchida

A nonstandard model for big-bang nucleosynthesis (BBN) is introduced in this talk. The standard theory of BBN developed after the famous paper written in 1948 by R. Alpher, H. Bethe, and G. Gamow, to have achieved a great success in describing the abundance of light nuclei in our universe. However, there remain some open questions such as the Lithium 7 problem. Attempts to model inhomogeneous big-bang nucleosynthesis (IBBN) is introduced, and so are the motivations for it and latest results.
In the standard BBN (SBBN) theory, homogeneity and isotropy of the distribution of all the constituents is assumed, as is supported by the Planck observation at large scales. In the IBBN models, on the contrary, baryon isocurvature perturbations at small scales is taken into account. Some theories lead to this situation, and the theory of baryogengesis from a (hyper)magnetic field is introduced as an example. Most IBBN studies simply use a 2-phase model, and the resultant nuclei abundance can be different from that SBBN predicts.
References:
[1] J. F. Lara, Phys. Rev. D 72.2, 023509 (2005).
[2] B. D. Fields, et al. JCAP 2020.03, 010 (2020).
[3] R. A. Malaney, and G. J. Mathews, Phys. Rept. 229.4 145-219 (1993).

2020/5/11 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報

Thermodynamical aspects of gravity and its application.

Takumi Hayashi

The entropy of the blackhole was proposed by Hawking and others several decades ago and developed into the notion of thermodynamics in gravity. It has still been intensively studied, because it could possibly offer the window to the nature of the quantum gravity such as the microstates of the theory.
In this seminor, I start from the emergence of thermodynamics at the classical BH horizon in the usual manner, and introduce the Euclidean analysis via quantum (or thermal) partition function, making use of Hamiltonian formulation of gravity.
Then I extend the thermodynamics to the modified gravity with higher curvatures with the help of the Wald’s entropy. I show examples in some theories how the entropy formula and thermodynamics works, and briefly introduce a recent application aimed at supporting the conjecture in quantum gravity.
The reference is listed below.
[1]T. Padmanabhan, Class. Quant. Grav.19 (2002) 5387-5408
[2]S. W. Hawking, Gary. T. Horowitz, Class. Quant. Grav. 13 (1996) 1487
[3]T. Jacobson, G. Kang, R. C. Myers, Phys. Rev. D 49 (1994) 6587
[4] C. Cheung, J. Liu, and G. N. Remmen, JHEP 10 (2018) 004

2020/4/27 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報

Gravitational Wave Production right after Primordial Black Hole Evaporation

Keisuke Inomata

We discuss the footprint of evaporation of primordial black holes (PBHs) on stochastic gravitational waves (GWs) induced by scalar perturbations. We consider the case where PBHs once dominate the Universe but eventually evaporate before the big bang nucleosynthesis. The reheating through the PBH evaporation could end with a sudden change in the equation of state of the Universe compared to the conventional reheating caused by particle decay. We show that this "sudden reheating" by the PBH evaporation enhances the induced GWs, whose amount depends on the length of the PBH-dominated era and the width of the PBH mass function.
We explore the possibility to constrain the primordial abundance of the evaporating PBHs by observing the induced GWs. We find that the abundance parameter \beta >~ 10^{-5} - 10^{-8} for O(10^3 - 10^5) g PBHs can be constrained by future GW observations if the width of the mass function is smaller than about a hundredth of the mass.
This seminar will be based on our recent work, arXiv:2003.10455.

2020/4/20 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報

Gravitational lensing of gravitational wave

Junya Kume

The effect of gravitational lensing on the propagation of gravitational wave (GW) have been extensively studied recently. Since the sensitivity of the GW detector improved and many GW events are now observed, we can have the opportunity to observe "lensed" GW.
In this seminar, I review the basic formulae of the gravitational lensing and explain what is the main difference between the lensing of light and that of GW. Then I briefly explain how this phenomena can affect observational result of GW from compact binary coalescence.

2020/4/13 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報

Deformation of the gravitational wave spectrum by density perturbations

Ryusuke Jinno

Abstract:
We study the effect of primordial scalar perturbations on the propagation of cosmological gravitational waves (GWs). We point out that such scalar perturbations deform the power spectrum of any stochastic GWs of the early-Universe origin. We first show that, adopting linear order results in scalar perturbations, this deformation is described by the convolution of the original GW spectrum and a linearly biased Gaussian kernel, and then discuss how large this effect can be, taking the latest bounds on primordial black holes (PBHs). We also point out that full understanding of this effect requires calculations of second order in scalar perturbations.

2020/4/6 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報

Time complexification for particle production

Soichiro Hashiba

Abstract:
Particle production, such as Hawking radiation, Schwinger effect and gravitational particle production, occurs in real time, however, we have to consider complex time in these phenomena for a proper estimation. That is because zeros of an effective frequency of a particle, which usually are located in complex time plane, plays a crucial role. Classically, a transition from a vacuum state to an excited state is prohibited anywhere but at these zeros, and in quantum field theory, a path integral picks up an effect of the zeros in complex time and particle production is realized. I will introduce several calculation methods of using time complexification for particle production. This talk will be mainly based on these papers:
Picard-Lefschetz theory - 1403.1277, 1510.03435, 1907.12224
Stokes phenomenon - 0911.4692, 1001.2933, 1004.2509, 1405.0302
fileseminar_note_Hashiba0407.pdf

2020/3/9 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報

Introduction to induced second-order gravitational waves

Minxi He

Abstract: This is a introductory talk about the induced second-order gravitational waves. As we know that gravitational wave (GW) astronomy is now one of the most popular topic in physics. In fact, GW is not only for astronomy but cosmology. The most famous example is the primordial GW predicted by inflation, although that is usually supposed to be detected by CMB b-mode. This talk will focus on higher frequency range of GW which could possibly detected by future interferometer GW detectors. The (non-)detection of these GW will give hints on cosmology, such as distinguishing cosmological models, and primordial black holes. This talk is based on the following papers:

https://arxiv.org/abs/gr-qc/0612013

https://arxiv.org/abs/hep-th/0703290

https://arxiv.org/abs/1804.08577

https://arxiv.org/abs/0812.4339

2018/3/12 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
Joint seminar at Waseda Univ.


2018/3/5 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
Speaker: Bernard Carr (Queen Mary University of London)
Title: Primordial Black Holes as Dark Matter and Seeds for Cosmic Structure
Abstract:
Primordial black holes (PBHs) larger than 10^{15}g are natural candidates for the dark matter but numerous constraints from lensing, dynamical and accretion effects imply that there are only a few allowed mass windows and the PBHs may need to have an extended mass function. The intermediate-mass window at 1–100 M⊙ is of special interest in view of the recent detection of black-hole mergers by LIGO. However, PBHs larger than this might have important consequences even if they provide only a small fraction of the dark matter. In particular, they could generate cosmological structure – including supermassive black holes, the first bound clouds and galaxies – through either the ‘seed’ effect or the ‘Poisson’ effect, thereby alleviating some problems associated with the standard CDM scenario. If the PBHs have an extended mass spectrum, they could both provide dark matter and generate cosmic structures. In this case, the stochastic gravitational wave background from the PBHs in this scenario would extend continuously from the LIGO frequency to the LISA frequency.


2018/2/27 (火)

UTAPwiki/セミナー/初期宇宙・相対論速報
Speaker: Takeshi Kobayashi (SISSA)
Title: Baryons, Dark Matter, and Light Scalars
Abstract:
The appearance of scalar fields with small masses is ubiquitous in physics beyond the Standard Model. In this talk I will describe how such light scalars can play important roles in cosmology, especially in connection to the origin of the baryons and dark matter of our universe. With regard to the baryons, I will show that a scalar with an approximate shift symmetry, such as the QCD axion, can naturally induce baryogenesis. For dark matter, I will present cosmological constraints on scalar dark matter obtained from analyses of the Lyman-alpha forest and the cosmic microwave background; here I will particularly focus on the ultralight regime and examine the long-standing claim that ultralight scalar dark matter may solve the small-scale issues of the CDM paradigm.


2018/2/26 (月)

UTAPwiki/セミナー/初期宇宙・相対論速報
No seminar due to the entrance exam



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