2022/7/4 (月)


Title: False vacuum decay in imaginary time and real time formalism

Speaker: Muzi Hong

The standard formalism for false vacuum decay is the instanton method developed by Coleman in the 1970s. It is an imaginary time formalism with Dirichlet boundary conditions. Recently, a method using classical-statistical approximation to describe false vacuum decay has been proposed. It calculates the classical evolution of the fields, and quantum effects enter in the choice of initial conditions. This method is a real time formalism and includes zero-point quantum fluctuations. In this seminar, I will review Coleman’s method and introduce the real time formalism, and estimate tunneling rate using both methods, which turn out to be similar. Interestingly, new simulation results published on arXiv last week show that the classical-statistical approximation predicts way much larger tunneling rate than the instanton method in 1+2 dimension. I will also present these results as well as previous simulation works, and try to explain why classical-statistical approximation actually gives different results other than instanton.

[1]Herzberg & Yamada, 1904.08565[hep-th]
[2]Coleman, Phys. Rev. D15, 2929(1977); Callan & Coleman, Phys. Rev. D16, 1762(1977)
[3]Polkovnikov, 0905.3384[cond-mat.stat-mech]
[4]Braden et al., 1806.06069[hep-th]
[5]Herzberg et al., 2009.00017[hep-th]
[6]Tranberg & Ungersback,2206.08691[hep-lat]
[7]Garcia-Bellido et al., 0208228[hep-ph]

2022/6/27 (月)


Title: Toward the Verification of the Equivalence Principle in the Quantum Regime

Speaker: Yoshio Kamiya

How can the gravitational interaction be understood on a microscopic scale, which is described by quantum mechanics? This seminar mainly introduces the experimental plan of testing the weak equivalence principle on the microscopic scale, as one of the experimental attempts to find clues for understanding gravity. The testing probes for this experiment are quantum bound states of neutrons on the earth’s gravity. I would like to discuss also about possibilities how we can utilise these kind of quantum probes for exploring quantum nature of gravity and the basic principle of quantum theory.

(+ AIP Conf. Proceedings 2319, 040017 (2021) "Experimental Search for Non-Newtonian Forces in the Nanometer Scale with Slow Neutrons”)
+ Nucl. Instrum. Methods A979, 164400 (2020) "Development of a Neutron Imaging Sensor using INTPIX4-SOI Pixelated Silicon Devices”
(+ Phys. Rev. Lett. 114, 161101 (2015) "Constraints on New Gravitylike Forces in the Nanometer Range”)
(+ Adv. in High Energy Phys. Vol.2014, 859241 (2014) "Precision Measurement of the Position-Space Wave Functions of Gravitationally Bound Ultracold Neutrons”)
+ Phys. Rev. Lett. 112, 071101 (2014) "Observation of the Spatial Distribution of Gravitationally Bound Quantum States of Ultracold Neutrons and Its Derivation Using the Wigner Function"

2022/6/20 (月)


Title: One-loop effect of 21-cm power spectrum


Speaker: Daisuke Yamauchi

In this talk, I discuss the one-loop effect due to the nonlinear growth of structure in
the context of the 21-cm line during dark ages (30<z<100). Observations of the redshifted
21-cm line of neutral hydrogen open up a new window for observational cosmology. Since
during dark ages most scales remain linear and the nonlinear growth is less effective, we
can in principle easily obtain predictable signals and use a large number of Fourier samples
which would drastically reduce the noise. In this talk, I briefly review the impact of the dark
age's 21-cm line on cosmology and I quantify the effect of the one-loop corrections on
the 21-cm power spectrum.

Yamauchi, 2203.15599
Floss, de Wild, Meerburg, Koopmans, 2201.08843
Munoz, Ali-Haimoud, Kamionkowski, PRD92, 083508 (2015)

2022/6/13 (月)


Title: Irreversible transformations in black-hole physics and the area quantization


Speaker: Naritaka Oshita

A black hole is one of the most mysterious and simplest objects in the Universe.
Especially, the similarity between black-hole physics and thermodynamics naturally
introduces the concept of black-hole entropy, which is represented by
(entropy) = (Black-Hole Area)/(4 * Planck Area).
This suggestive formula implies that there exists a “bit”,
whose size is of the order of the Planck area, on the black hole horizon.
This picture was originally introduced by Bekenstein [1] without relying on the entropy formula.
I will review the reversible and irreversible transformations of a black hole [2]
and then will explain how such an interesting picture was introduced by him.

[1] J. D. Bekenstein, Phys. Rev. D 7, 2333 (1973).
[2] D. Christodoulou, PRL 25, 22 (1970).

2022/6/6 (月)


Title: Measurement of gravitational waves using squeezed light


Speaker: Jun'ichi Yokoyama

Laser interferometer gravitational wave detectors suffer from
many different noise sources. Among them those related with
laser power is shot noise and radiation pressure noise which have
opposite dependence on it, so that there is a lower bound on the
achievable sensitivity called quantum limit. It is known, however,
that using squeezed light we may overcome the simple quantum
limit. I would like to introduce it paying attention to the similarity
to quantum field theory in curved spacetime

"Conversion of conventional gravitatioanl-wave interferometers into
quantum nondemolition interferometers by modifying their input
and/or output optics" H.J. Kimble, Y. Levin, A.B. Matsko,
K.S. Thorne, and S.P. Vyatchanin, Phys. Rev. D65(2001)022002
"Frequency-Dependent squeezed vacuum source for broadband
quantum noise reduction in advanced gravitational wave detectors"
Y.Zhao, N. Aritomi, E. Capocasa, M. Leonardi, ..etal
Phys Rev Lett 124(2020)171101
"Frequency-dependent squeezing for advanced LIGO"
L. McCuller, C. WHittle, D. Ganapathy, K. Komori, et al
Phys Rev Lett 124(2020)171102
The latter two papers were published in sequence; the former reports
an experiment at NAOJ.

2022/5/30 (月)


Title: Consistency relation in large scale structure and bootstrap: a missing piece?

Speaker: Tomohiro Fujita

Soft theorem, which relates n- and (n+1)-point correlation functions in the soft momentum limit, is generally found in a field theory with a symmetry. In the perturbative approach towards large scale structure (LSS) in our Universe, the soft theorem is called consistency relation and has been of interest from both theoretical and observational perspectives, since it was first proposed in 2013. However, we suspect that the known set of the consistency relation of LSS may not be complete. This is because, when we construct a general solution by using the consistency relation (or "bootstrap" a solution), the obtained solution contains an unphysical component which results in inconsistent behaviors of the correlation functions (e.g. one-loop power spectrum is undetermined). In this seminar talk, I will not provide a solution to this problem. Nevertheless, I will introduce the consistency relation of LSS and explain the problem. If time allows, I will also discuss a possible way to find a missing piece of the consistency relations.

[1] arXiv:1311.0290
[2] arXiv:1311.1236
[3] arXiv:2003.10114
[4] arXiv:2103.08649

2022/5/23 (月)


Monday seminar will be skipped, but we will attend Moriya-san's seminar about supernovae instead.

2022/5/16 (月)


Title: Chiral Kinetic Theory in the Wigner Function Formalism

Speaker: Kohei Kamada

Chiral magnetic effect is now known as an important effect not only
for the topics originally considered, such as the heavy ion collision
or Weyl semimetals, but also for compact stars and primordial magnetic fields.
I have explained how it is derived from the chiral anomaly by using
the Nielsen-Ninomiya approach (zero temperature) and magnetohydrodynamics
(local thermal equilibrium). However, it is desirable if we can write down
the kinetic equation (or Boltzmann equation) that consistently takes into account
the chiral effect to follow the out-of-equilibrium dynamics.
The kinetic equation with the Berry curvature is one direction,
but it is noticed that the Lorentz invariance is not apparent in this formalism.
In this talk, I will introduce the kinetic theory with the Wigner function whose
Lorentz invariance is a manifest. If time allows, I will explain the extension
to the curved spacetime and application to the electron-neutrino-proton-neutron plasma.

[1] Yoshimasa Hidaka, Shi Pu, Di-Lun Yang, arXiv:1612.04630, Phys. Rev. D 95, 091901 (2017)
[2] Yu-Chen Liu, Lan-Lan Gao, Kazuya Mameda, Xu-Guang Huang, arXiv:1812.10127, Phys. Rev. D 99, 085014 (2019)
[3] Naoki Yamamoto, Di-Lun Yang, arXiv:2002.11348, Astrophys.J. 895 (2020) 1
[4] Naoki Yamamoto, Di-Lun Yang, arXiv:2103.13159, Phys. Rev. D 104, 123019 (2021)

2022/5/9 (月)


Title: Capture of Electroweak Multiplet Dark Matter in Neutron Stars

Speaker: Motoko Fujiwara

If Dark Matter (DM) has a sizable scattering cross section with nucleons, it can efficiently be captured by a neutron star. Its energy is then transferred to the neutron star as heat through the scattering and annihilation inside the star. This heating effect may be detectable via dedicated temperature observations of nearby old pulsars, providing an alternative method for DM searches. We show that, for electroweak multiplet DM, this search strategy can probe the parameter region that is out of reach of future DM direct detection experiments. To see this systematically, we classify such DM candidates in terms of their electroweak charges and investigate the effect of ultraviolet physics using higher-dimensional effective operators. We then show that if the effect of ultraviolet physics is sizable, the DM-nucleon elastic scattering cross section becomes sufficiently large, whilst if it is suppressed, then the mass splittings among the components of the DM multiplet get small enough so that the inelastic scattering processes are operative. In any case, the electroweak multiplet DM particles are efficiently captured in neutron stars, making the search strategy with the temperature observation of old neutron stars promising.

[1] https://arxiv.org/abs/2204.02238

2022/5/2 (月)


Title: Analytical approximation of primordial black hole formation by an ultra slow-roll period

Speaker: Jason Kristiano

Primordial quantum fluctuations that are stretched by cosmic inflation can explain the anisotropy of cosmic microwave background (CMB). Such fluctuations have a long wavelength and the amplitude of the power spectrum is constrained to be around 10^(-9) by observation. However, at small scales, fluctuations with wavelength much smaller than CMB scales, the observational constraints are very loose. Theoretically, if there is a peak with order of 10^(-2) in the amplitude of the power spectrum at small scales, it can collapse into primordial black hole (PBH). In this seminar, I will show how to form this peak at small scales analytically. I will explain the formation of PBH generated by a short ultra slow-roll (USR) period right before the end of inflation.

[1] J. Liu, et. al., Analytical approximation of the scalar spectrum in the ultraslow-roll inflationary models, Phys. Rev. D 101, 083535 (2020), arXiv:2003.02075.
[2] M. Biagetti, et. al., Primordial Black Holes from Inflation and Quantum Diffusion, JCAP 07 (2018) 032, arXiv:1804.07124.

2022/4/25 (月)


Title: Brown–Teitelboim mechanism

Speaker: Fumio Uchida

The cosmological constant problem is a serious naturalness problem in cosmology. One of the most popular approaches to the problem is the Brown–Teitelboim mechanism. In the mechanism, four-form gauge fluxes play the role of the cosmological constant, and the controversial anthropic argument is employed. In the talk, I will explain the idea of Bousso–Polchinski [1], which overcomes a drawback of Brown–Teitelboim’s original idea [2], and its recent extension [3] that tries to address the Higgs naturalness problem as well.

[1] R. Bousso, and J. Polchinski, JHEP 06 (2000) 006 [arXiv: hep-th/0004134]
[2] J. Brown, and C. Teitelboim PLB 195, 177 (1987), J. Brown, and C. Teitelboim Nucl. Phys. B 297, 787 (1988) as the original ideas; R. Bousso, Gen. Relativ. Gravit. 40, 607 (2008) [arXiv: 0708.4231] for a review
[3] M. Moretti, and F. Pedro (2022) [arXiv:2202.07004]

2022/4/18 (月)


Title: tail structure of primordial perturbations and implications for primordial black holes

Speaker: Koki Tokeshi

Primordial curvature perturbations are known to be nearly Gaussian according to the large scale observations.
However, it does not necessarily mean that at much smaller scales they are also Gaussian distributed.
Indeed, one can see that these tails are highly non-Gaussian making use of the framework of stochastic inflation.
Since primordial black holes could be generated from the tail of the distribution, it is expected that this modification affects the pbh abundance.
In particular, the distribution decays exponentially and hence the abundance is predicted to increase by several or many orders.

[1] C. Pattison, V. Vennin, H. Assadullahi, and D. Wands, JCAP 10 (2017) 046 [hep-th/1707.00537]
[2] J. M. Ezquiaga, J. Garcia-Bellido, and V. Vennin, JCAP 03 (2020) 029 [astro-ph.CO/1912.05399]

2022/4/11 (月)


Title: A New Conserved Charge in General Relativity

Speaker: Takumi Hayashi

Defining conserved energy in general relativity is not straightforward due to the ambiguity of the energy of the gravity, and several definition has been proposed, including Einstein pseudotensor, Komar integral(for static spacetime), ADM mass(for asymptotically flat spacetime) and so on. But it is recently pointed out by the papers [2][3] that conservation of all these energies are merely off-shell identities based on the Noether’s 2nd theorem, rather than the consequence of the dynamics. In this talk, I review their discussion on the existing definitions of gravitational energy, and introduce the new conserved charge they proposed, providing several examples of application to the various (static and non static) spacetimes.

[1] Sebastian De Haro (2021), [arXiv:2103.17160].
[2] Sinya Aoki, Tetsuya Onogi, Shuichi Yokoyama (2021), [arXiv:2103.17160].
[3] Sinya Aoki, Tetsuya Onogi (2022), [arXiv:2201.09557].

2022/2/28 (月)


Title: A Nelson-Barr model

Speaker: Kohei Fujikura

Several solutions to the strong CP problem including QCD axion have been proposed so far. One possible solution to the strong CP problem is that CP is an exact symmetry, spontaneously broken at some scale. Nelson and Barr constructed the simple phenomenologically viable models in this framework called Nelson-Barr models [1,2]. In this talk, I will review the general features of a Nelson-Barr model and show that a Nelson-Barr model with gauge-mediated supersymmetry breaking is a plausible solution to the strong CP problem. This talk is based on Ref. [3] and the review of a Nelson-Barr model [4].
[1]:A.E. Nelson, Naturally Weak CP-violation, Phys. Lett. B 136 (1984) 387
[2]:S.M. Barr, Solving the Strong CP Problem Without the Peccei-Quinn Symmetry, Phys. Rev. Lett. 53 (1984) 329.
[3]:K. Fujikura, Y. Nakai, R. Sato and M. Yamada, Baryon Asymmetric Universe from Spontaneous CP Violation, [2202.08278]
[4]:M. Dine and P. Draper, Challenges for the Nelson-Barr Mechanism, JHEP 08 (2015) 132 [1506.05433].

2022/2/21 (月)


Title: A few things about entanglement in QFT

Speaker: Yusuke Yamada

Abstract: Entanglement is a characteristic property of quantum theory that has no analogue in classical physics. Although entanglement in quantum theory with finite degrees of freedom is relatively simple, for the case with infinite number of degrees of freedom, such as quantum field theory, we need to be careful since the notions of density matrix, entanglement entropy..etc. are subtle.
Entanglement is a characteristic property of quantum theory that has no analogue in classical physics. Although entanglement in quantum theory with finite degrees of freedom is relatively simple, for the case with infinite number of degrees of freedom, such as quantum field theory, we need to be careful since the notions of density matrix, entanglement entropy..etc. are subtle.
In this talk, I will briefly review how QFT Hilbert space is different from that in QM with finite d.o.fs. and then review a few topics related to entanglement in QFT.

E. Witten, Rev.Mod.Phys. 90 (2018) 4, 045003 [arXiv:1803.04993]
E. Witten, arXiv: 2112. 11614

2022/1/31 (月)


Title: Transport coefficients from the linear response theory and its application to cosmology

Speaker:Kohei Kamada

Transport phenomenon is of interest for the statistical mechanics and has been extensively
studied in the broad range of the fields of physics. In particular, the transport coefficients
that relate the flow of the physical quantities and the parameters of the system is important
to follow the evolution of the system in a consistent way. In cosmology, the evolution of
the particle number densities with their interactions and magnetohydrodynamics can be
understood as the transport phenomena. In these cases, the transport coefficients are
identified as the scattering rate, electric conductivity, viscosity, and so on.
In this talk, I will introduce the way to calculate these transport coefficients from
the linear response theory with the quantum field theory. I will derive the formula to estimate
the electric conductivity and the kinetic equation for the spontaneous baryogenesis,
which has only been intuitively given.

[1] D. Zubarev “Nonequilibrium Statistical Thermodynamics” 1971, Nauka, Moskow
[2] A. Hosoya, M. Sakagami, M. Takao, Annals of Physics 154, 229-252, 1984
[3] V. Domcke, Y. Ema, K. Mukaida, M. Yamada, JHEP08 (2020) 096

2022/1/17 (月)


Title: Toward nonlinear extension of the independent component analysis

Speaker: Jun'ichi Yokoyama

Abstract: After reviewing the conventional independent component analysis
which assumes linear relations between various channels, I extend the theory
to the case they have nonlinear dependence.

[1] Morisaki et al. Proc.Japan Acad.B 92 (2016) 336
[2] in preparation

2021/12/13 (月)


Title: A brief introduction to the model of solid inflation

Speaker: Koki Tokeshi

Abstract: Many inflationary models can be treated in the framework of the conventional effective field theory approach, in which the time translation symmetry slightly breaks to realize quasi de Sitter Universe [2]. The model of solid inflation, proposed and systematically analyzed in [1], gives an exception: the spatial translation symmetries are broken in the model. In this talk, I will review the model and introduce many unusual features stemmed from the drastically different symmetry breaking pattern. Since the scalar amplitude could be enhanced compared to the conventional prediction, I will also discuss possibility of black hole formation in the model [3].
[1] S. Endlich, A. Nicolis, and J. Wang, ‘Solid inflation,’ JCAP 10 (2013) 011.
[2] C. Cheung, L. Fitzpatrick, J. Kaplan, and L. Senatore, ‘The effective field theory of inflation,’ JHEP 03 (2008) 014.
[3] G. Ballesteros, J. Jimenez, M. Pieroni, ‘Black hole formation from a general quadratic action for inflationary primordial fluctuations,’ JCAP 06 (2019) 016.

2021/11/29 (月)


Title: Introduction to generalized global symmetries and their application

Speaker: Yoshimasa Hidaka

Ordinary symmetries are symmetries acting on point particles. The concept can be generalized to symmetries acting on extended objects, such as vortices and domain walls. Such symmetres are called higher form symmetries. In this talk, I review the concept of higher form symmetries. As an example of the application, I discuss spontaneous breaking of higher form symmetries in a nonrelativistic system and show the counting rule of the Nambu-Goldstone modes.

2021/11/22 (月)


Dear all,

Next RESCEU Monday seminar is on Nov. 22, 15:30-16:30.
The seminar is the continuation of the last seminar, and the information is as follows.


Title:Two-group symmetry in QED

Speaker:Fumio Uchida

Symmetry is one of the most fundamental concepts in physics. However, well-known symmetries as of the Standard Model belong to just the simplest class of its generalizations [1-3]. In the talk, we will see two-group symmetry in massless and multi-flavor QED, as an explicit example of the wider symmetry class. I hope the talk will be complementary to the forthcoming lecture [4].

[1] D. Gaiotto, et al. “Generalized global symmetries,” JHEP 02, 172 (2015), arXiv:1412.5148 [hep-th].
[2] E. Sharpe, “Notes on generalized global symmetries in QFT,” Fortsch. Phys. 63, 659 (2015), arXiv:1508.04770 [hep-th].
[3] C. Cordova, et al. “Exploring 2-Group Global Symmetries,” JHEP 02, 184 (2019), arXiv:1802.04790 [hep-th].
[4] Prof. Hidaka’s lecture, assigned to the next slot of our seminar series, about generalized symmetry.

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