![[PukiWiki]](image/pukiwiki.png "[PukiWiki]")
2022/7/18 (月)National holiday. 2022/7/11 (月)Hong-san continues her seminar last week. 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] 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. References: 2022/6/20 (月)Title: One-loop effect of 21-cm power spectrum †15:00- †Speaker: Daisuke Yamauchi †In this talk, I discuss the one-loop effect due to the nonlinear growth of structure in reference: 2022/6/13 (月)Title: Irreversible transformations in black-hole physics and the area quantization †13:00- †Speaker: Naritaka Oshita †A black hole is one of the most mysterious and simplest objects in the Universe. [1] J. D. Bekenstein, Phys. Rev. D 7, 2333 (1973). 2022/6/6 (月)Title: Measurement of gravitational waves using squeezed light †13:00- †Speaker: Jun'ichi Yokoyama †Laser interferometer gravitational wave detectors suffer from References 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 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 [1] Yoshimasa Hidaka, Shi Pu, Di-Lun Yang, arXiv:1612.04630, Phys. Rev. D 95, 091901 (2017) 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. 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] 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. [1] C. Pattison, V. Vennin, H. Assadullahi, and D. Wands, JCAP 10 (2017) 046 [hep-th/1707.00537] 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]. 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]. 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. Ref: 2022/1/31 (月)Title: Transport coefficients from the linear response theory and its application to cosmology †Speaker:Kohei Kamada †Abstract: References: 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 References: 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]. |