Ya-Wen Sun, University of Chinese Academy of Sciences
[QCD theory seminar] Topological modes in relativistic hydrodynamics
Online (Zoom)
In this talk I will show that gapless modes in relativistic hydrodynamics could become topologically nontrivial by weakly breaking the conservation of energy momentum tensor in a specific way. These energy momentum non-conservation terms could naturally be produced by an external gravitational field that comes from a coordinate transformation from the flat spacetime. This suggests that topologically trivial modes could become topologically nontrivial by being observed in a special non-inertial reference frame. I will also introduce a possible holographic realization of this system.
Daisuke Yamauchi, Kanagawa U
[Cosmophys seminar] Testing dark energy with cosmological and astrophysical observations
Online (Zoom)
In the era of precision cosmology, one of the biggest challenges of modern cosmology is the elucidation of the origin of the late time acceleration of the Universe. The most straightforward candidate of its origin, often referred to as dark energy, is a cosmological constant, but there are other various candidates that are still worth considering and should be distinguished by future observations. In this talk, I will consider two interesting possibilities as other candidates of dark energy: One is the modification of gravity theory. We construct the general framework of the scalar-tensor theories that has been developed so far and show that the resultant theories generally break the screening mechanism only inside astrophysical bodies, which leads to a novel probe of dark energy. Other is the remnant of quantum tunneling of the Universe. When we consider the open Universe created by bubble nucleation, the residual of the ancestor vacuum, that is the vacuum energy of the supercurvature mode, can be regarded as a possible candidate of dark energy. we discuss the detectability of this new idea by future observations.
Toyokazu Sekiguchi, KEK
[Cosmophys seminar] Early recombination meets closed Universe: more than a solution to the H0 tension
Online (Zoom)
The discrepancy in measurements of H_0 is the most notable anomaly in contemporary cosmology with significance as large as 6σ. Despite many attempts, there is yet no compelling solution to the H_0 tension. In the first part of my talk, I review the H_0 tension. In particular, I will clarify why it is so diffcult to solve the tension. In the latter part, I will present our model, which is based on modified recombination in a closed Universe. Starting from general discussion on necessary conditions that successful modified recombination models should satisfy to fit CMB observations, I will demonstrate time-varying m_e models indeed satisfy those conditions. To fit low-z distance measurements such as baryon acoustic oscillation and type-Ia supernovae, a positive spatial curvature plays an essential role. Compared to the canonical ΛCDM, our model improves the chi-square by more than 23. We also show our model solves the lensing anomaly in Planck data concurrently.
Shota Imaki, University of Tokyo
[QCD theory seminar] Chiral magnetic effect in the hadronic phase
Online (Zoom)
We study the chiral magnetic effect (CME) in the hadronic phase. The CME current involves pseudoscalar mesons to modify its functional form. This conclusion is independent of microscopic details. The strength of the CME current in the hadronic phase would decrease for two flavors.
Yohei Ema, DESY
Higgs inflation, unitarity, and emergence of scalaron
Online (Zoom) https://kds.kek.jp/indico/event/34753/
The Higgs inflation introduces a large non-minimal coupling between the Ricci scalar and Higgs that causes tree-level unitarity violation well below the Planck scale. After reviewing the unitarity issue during and after inflation, we show that the unitarity can be restored by summing over vacuum polarization-type diagrams. The scattering amplitude develops a pole after the resummation, which we identify as the scalar component of the metric, or the scalaron. It suggests that the Higgs inflation is actually a multi-field inflation model, i.e. Higgs and the scalaron, and does not suffer from the unitarity issue. We also show that this phenomenon can be understood in the language of the non-linear sigma model (NLSM), with the scalaron identified as the sigma field that linearizes the NLSM.
Takahiko Matsubara, KEK
[Cosmophys seminar] Weakly non-Gaussian formula for Minkowski functionals in general dimensions
Online (Zoom) The Minkowski functionals are useful statistics to quantify the morphology of various random fields. They have been applied to a large number of analyses of geometrical patterns, including various types of cosmic fields, morphological image processing, etc. In some cases, including cosmological applications in particular, small deviations from Gaussianity of distribution have a fundamental importance. Analytic formulas of expectation values of Minkowski functionals with small non-Gaussianity have been derived in limited cases so far. We generalize the previous work to derive an analytic expression for expectation values of Minkowski functionals up to second-order corrections of non-Gaussianity in a space of general dimensions. The derived formula has sufficient generality to be applied to any random fields with weak non-Gaussianity in a statistically homogeneous and isotropic space of any dimensions.
The Minkowski functionals are useful statistics to quantify the morphology of various random fields. They have been applied to a large number of analyses of geometrical patterns, including various types of cosmic fields, morphological image processing, etc. In some cases, including cosmological applications in particular, small deviations from Gaussianity of distribution have a fundamental importance. Analytic formulas of expectation values of Minkowski functionals with small non-Gaussianity have been derived in limited cases so far. We generalize the previous work to derive an analytic expression for expectation values of Minkowski functionals up to second-order corrections of non-Gaussianity in a space of general dimensions. The derived formula has sufficient generality to be applied to any random fields with weak non-Gaussianity in a statistically homogeneous and isotropic space of any dimensions.
This talk is based on a paper in preparation with Satoshi Kuriki (ISM).
Riki Toshio, Kyoto University
[QCD theory seminar] Anomalous Hydrodynamic Transport in Interacting Noncentrosymmetric Metals
Online (Zoom) In highly conductive metals with sufficiently strong momentum-conserving scattering, the electron momentum is regarded as a long-lived quantity, whose dynamics is described by an emergent hydrodynamic theory. Actually, such hydrodynamic behaviors have been reported, since 2016, in various ultrapure materials such as GaAs quantum wells [1], 2D monovalent layered metal PdCoO2 [2], Weyl semimetal WP2 [3] and graphene [4-6] through various unconventional DC transport phenomena. However, in spite of a rapidly increasing number of reports on the candidates, it remains an unexplored important issue what kind of roles the crystal symmetry and the geometry of Bloch electrons play in the hydrodynamic transport. In this work [7], we formulate the hydrodynamic theory for time-reversal-symmetry preserved noncentrosymmetric metals. The obtained equations reveal the emergence of unprecedented anomalous forces in the Euler equation, which highlights an unexpected analogy between our fluids and the inviscid chiral fluids in vacuum. It is remarkable that this analogy indicates the existence of vorticity-induced electric current (we refer to it as generalized vortical effect) in condensed matter without nontrivial topology, which is a phenomenon analogous to the chiral vortical effect in chiral fluids. In particular, we reveal that this novel phenomenon gives rise to a novel anomalous hydrodynamic flow, that is, the anomalous edge current and the asymmetric Poiseuille flow. Furthermore, our theory is also able to describe the hydrodynamic counterparts of various nonlinear anomalous transport phenomena which has been formulated so far only in dissipative or ballistic regime. For example, the anomalous transport corresponding to so-called the quantum nonlinear Hall effect and the magnus Hall effect are integrated into a unified framework described by the velocity field in our work. Furthermore, towards an experimental observation of the predicted phenomena, we provide a symmetry consideration on the existing hydrodynamic materials and also give a quantitative estimation of the observable quantities, based on an effective model for strained-TMD and graphene.
In highly conductive metals with sufficiently strong momentum-conserving scattering, the electron momentum is regarded as a long-lived quantity, whose dynamics is described by an emergent hydrodynamic theory. Actually, such hydrodynamic behaviors have been reported, since 2016, in various ultrapure materials such as GaAs quantum wells [1], 2D monovalent layered metal PdCoO2 [2], Weyl semimetal WP2 [3] and graphene [4-6] through various unconventional DC transport phenomena. However, in spite of a rapidly increasing number of reports on the candidates, it remains an unexplored important issue what kind of roles the crystal symmetry and the geometry of Bloch electrons play in the hydrodynamic transport. In this work [7], we formulate the hydrodynamic theory for time-reversal-symmetry preserved noncentrosymmetric metals. The obtained equations reveal the emergence of unprecedented anomalous forces in the Euler equation, which highlights an unexpected analogy between our fluids and the inviscid chiral fluids in vacuum. It is remarkable that this analogy indicates the existence of vorticity-induced electric current (we refer to it as generalized vortical effect) in condensed matter without nontrivial topology, which is a phenomenon analogous to the chiral vortical effect in chiral fluids. In particular, we reveal that this novel phenomenon gives rise to a novel anomalous hydrodynamic flow, that is, the anomalous edge current and the asymmetric Poiseuille flow. Furthermore, our theory is also able to describe the hydrodynamic counterparts of various nonlinear anomalous transport phenomena which has been formulated so far only in dissipative or ballistic regime. For example, the anomalous transport corresponding to so-called the quantum nonlinear Hall effect and the magnus Hall effect are integrated into a unified framework described by the velocity field in our work. Furthermore, towards an experimental observation of the predicted phenomena, we provide a symmetry consideration on the existing hydrodynamic materials and also give a quantitative estimation of the observable quantities, based on an effective model for strained-TMD and graphene.
[1] L. W. Molenkamp and M. J. M. de Jong, Phys. Rev. B 49, 5038 (1994).
[2] P. J. W. Moll, et al., Science 351, 1061 (2016),
[3] J. Gooth, et al., Nature Communications 9, 4093 (2018).
[4] D. A. Bandurin, et al., Science 351, 1055 (2016).
[5] J. Crossno, et al., Science 351, 1058 (2016).
[6] R. K. Kumar, et al., Nature Physics 13, 1182 (2017).
[7] RT, K. Takasan, N. Kawakami, arXiv:2005.03406 (2020).
Kyohei Mukaida, DESY
Baryogenesis from Axion Inflation
Online (Zoom) https://kds.kek.jp/indico/event/34874/
In inflation models driven by an axion-like particle, the inflaton may have a Chern-Simons coupling to the Standard Model (SM) U(1)_Y. In this talk, we show that this setup is a highly predictive baryogenesis model without further ingredients other than the SM and the inflaton. During inflation, this Chern-Simons coupling sources a dual production of the SM chiral fermions and maximally helical U(1)_Y gauge fields, associated with the SM chiral anomaly equation. The anomalous transport of these primordial chiral asymmetries and the helical U(1)_Y gauge fields after inflation gives rise to the present baryon asymmetry. The observed baryon asymmetry can be reproduced if the Hubble parameter of inflation is around Hinf ~ 10^10 – 10^12 GeV with moderate dependence on inflation model parameters.
木村裕介, KEK
理論センタープロジェクト「弦からヒッグズ／フレーバー」セミナー 1/2 Calabi-Yau 4-folds and 4D F-theory on the double covers
Online (Zoom)
詳しくはプロジェクトのページhttps://www2.kek.jp/theory-center/project/string2higgsflavor/2020/06/15/projectseminar_halfcy/をご覧ください。
Shigenori Seki, Doshisha
Formulation and Evaluation of Entanglement Entropy in Elastic Scattering
Online (Zoom) https://kds.kek.jp/indico/event/34653/
