Kallol Sen, IPMU, University of Tokyo
A mellin space approach to the conformal bootstrap
Meeting room 1, Kenkyu honkan 1F
We describe in more detail our approach to the conformal bootstrap which uses the Mellin representation of CFT_d four point functions and expands them in terms of crossing symmetric combinations of AdS_d+1 Witten exchange functions. We consider arbitrary external scalar operators and set up the conditions for consistency with the operator product expansion. Namely, we demand cancellation of spurious powers (of the cross ratios, in position space) which translate into spurious poles in Mellin space. We discuss two contexts in which we can immediately apply this method by imposing the simplest set of constraint equations. The first is the epsilon expansion. We mostly focus on the Wilson-Fisher fixed point as studied in an epsilon expansion about d=4. We reproduce Feynman diagram results for operator dimensions to O(ϵ^3)rather straightforwardly. This approach also yields new analytic predictions for OPE coefficients to the same order which fit nicely with recent numerical estimates for the Ising model (at ϵ=1). We will also mention some leading order results for scalar theories near three and six dimensions. The second context is a large spin expansion, in any dimension, where we are able to reproduce and go a bit beyond some of the results recently obtained using the (double) light cone expansion. We also have a preliminary discussion about numerical implementation of the above bootstrap scheme in the absence of a small parameter.
Tsuyoshi Houri, Kobe University
Conformal symmetry of spacetime and ladder operators of the Laplacian
Meeting room 1, Kenkyu honkan 1F
It is well known that if a spacetime admits isometry, the space of eigenfunctions for the Laplacian is given as a representation of the isometry group provided an eigenvalue is fixed. In contrast, it has been less known how conformal symmetry of spacetime is related to the Laplacian. In this talk, we first revisit a relation between conformal symmetry of the two-dimensional sphere and ladder operators for the spherical harmonics. After that, we generalise the relation in a certain class of spacetimes which includes maximally symmetric spacetimes. As an application, we discuss the horizon instability of an extreme Reissner-Nordstrom black hole.
Takahiro Hayashinaka, RESCEU
Fermionic Schwinger effect in 1+3 dimensional de Sitter spacetime
Meeting room 1, Kenkyu honkan 1F We explored Schwinger effect of spin 1/2 charged particles with static electric field in 1+3 dimensional de Sitter spacetime [1]. The vacuum expectation value of the spinor current which is induced by the produced particles in the electric field was analytically calculated. We find that the current becomes negative, namely it flows in the direction opposite to the electric field, if the electric field is weaker than a certain threshold value depending on the fermion mass, which is also known to happen in the case of scalar charged particles in 1+3 de Sitter spacetime. We also investigated the implications of the result in detail.
We explored Schwinger effect of spin 1/2 charged particles with static electric field in 1+3 dimensional de Sitter spacetime [1]. The vacuum expectation value of the spinor current which is induced by the produced particles in the electric field was analytically calculated. We find that the current becomes negative, namely it flows in the direction opposite to the electric field, if the electric field is weaker than a certain threshold value depending on the fermion mass, which is also known to happen in the case of scalar charged particles in 1+3 de Sitter spacetime. We also investigated the implications of the result in detail.
References
[1] T. Hayashinaka, T. Fujita and J. Yokoyama, JCAP 1607 (2016) 07 010, arXiv: 1603.04165
[2] only a partial list of recent works on the subject: T. M. B. Frob, J. Garriga, S. Kanno, M. Sasaki, J. Soda, T. Tanaka, and A. Vilenkin, JCAP 2014 (2014) 04 009, R. G. Cai and S. P. Kim, JHEP 09 (2014) 072, T. Kobayashi and N. Afshordi, JHEP 2014 (2014) 10 1-36, C. Stahl, E. Strobel, and S. S. Xue, Phys. Rev. D 93 (Jan, 2016) 025004, E. Bavarsad, C. Stahl, and S. S. Xue, arXiv:1602.0655, C. Stahl and S. Xue Phys.Lett. B760 (2016) 288-292, T. Hayashinaka and J. Yokoyama, JCAP 1607 (2016) 07 012, arXiv:1603.0617
Da-Shin Lee, National Dong-Hwa University
Analog Model of Quantum Phenomena in Curved Spacetime Using Cold Atomic Condensates
Meeting room 3, Kenkyu honkan 1F We explore possible analogies between quantum phenomena in curved spacetime and cold laboratory condensates whose speed of sound can be tuned by means of an external field. In the first instance, the creation of causal horizons when a system undergoes rapid changes can lead to the creation of defects e.g. cosmic strings and monopoles. We see to what extent this can be mimicked in condensates by the spontaneous creation of vortices in a field ramp. Secondly, by examining the phonon geodesics in the acoustic metric we can look for spontaneous phonon creation that mimics spontaneous particle creation in curved space-time. Also, the fluctuating nature of the phonon background suggests analogies with quantum gravity.
We explore possible analogies between quantum phenomena in curved spacetime and cold laboratory condensates whose speed of sound can be tuned by means of an external field. In the first instance, the creation of causal horizons when a system undergoes rapid changes can lead to the creation of defects e.g. cosmic strings and monopoles. We see to what extent this can be mimicked in condensates by the spontaneous creation of vortices in a field ramp. Secondly, by examining the phonon geodesics in the acoustic metric we can look for spontaneous phonon creation that mimics spontaneous particle creation in curved space-time. Also, the fluctuating nature of the phonon background suggests analogies with quantum gravity.
References:
[1] D.-S. Lee, C. Y. Lin, and R. J. Rivers: “Derivation of Hydrodynamics for the Gapless Mode in the BEC-BCS Crossover from the Exact One-Loop Effective Action,” Phys. Rev. Lett. 98, 020603 (2007).
[2] C.-Y. Lin, D.-S. Lee, and R. J. Rivers, “The role of Causality in Tunable Fermi Gas Condensates,” J. Phys. Cond. Matter 25, 04211 (2013).
[3] J.-T. Hsiang, C.-Y. Lin, D.-S. Lee, and R. J. Rivers, “Quantum Stochastic Behavior in Cold Fermi Gases: Phonon Propagation,” Phys. Rev. A 91, 051603(R) (2015).
Naoki Yoshida, Tokyo Univ.
Cosmological constraints on dark matter annihilation and decay
Meeting room 3, Kenkyu honkan 1F
We present the results from cross-correlation analysis of weak gravitational lensing and the extra-galactic gamma-ray radiation. The former provides the large scale distribution of dark matter, and the latter possibly includes high energy photons produced by dark matter self-annihilation or decay. We use data from CFHT, SDSS, RCSLens galaxy surveys and the Fermi all-sky survey. We generate a large set of full-sky mock catalogs from cosmological N-body simulations and use them to estimate statistical errors accurately. The measured cross-correlation is consistent with null detection, which is then used to place strong cosmological constraints on annihilating and decaying DM. For leptophilic DM, the constraints are improved by a factor of 100 in the mass range of ~TeV when including contributions from secondary gamma-rays due to the inverse -Compton upscattering of background photons. Annihilation cross sections of 10^{-23} cm3/s are excluded for TeV-scale DM. Lifetimes of 10^25 sec are also excluded for the decaying TeV-scale DM. These are real cosmological constraints, rather than being obtained from local structures.
Eigo Shintani, RIKEN-AICS
Lattice computation of nucleon matrix element related to BSM physics
Meeting room 1, Kenkyu honkan 1F
I will review the recent nucleon matrix element computation related to BSM physics, e.g. EDM, proton decay, etc, in lattice QCD.
Hiroaki Sugiyama, Toyama Univ.
Exploring neutrino mass generation mechanisms via the lepton flavor violating decay of the Higgs boson
Meeting room 1, Kenkyu honkan 1F There are many new physics models for generating neutrino masses, and it is important to consider how these models can be experimentally discriminated. Classification of models is useful for the efficient discrimination. In this talk, we classify simple models for each of Majorana and Dirac neutrino masses by concentrating on Yukawa interactions with leptons. We see that, if a lepton flavor violating decay of the Higgs boson is discovered, simple models for Majorana neutrino masses are excluded while some models for Dirac neutrino masses can survive.
There are many new physics models for generating neutrino masses, and it is important to consider how these models can be experimentally discriminated. Classification of models is useful for the efficient discrimination. In this talk, we classify simple models for each of Majorana and Dirac neutrino masses by concentrating on Yukawa interactions with leptons. We see that, if a lepton flavor violating decay of the Higgs boson is discovered, simple models for Majorana neutrino masses are excluded while some models for Dirac neutrino masses can survive.
[1] S. Kanemura and H. Sugiyama, Phys. Lett. B753, 161 (2016). [2] S. Kanemura, K. Sakurai and H. Sugiyama, Phys. Lett. B758, 465 (2016). [3] M. Aoki, S. Kanemura, K. Sakurai and H. Sugiyama, Phys. Lett. B763, 352 (2016).
Ignatios Antoniadis, University of Bern
Aspects of string phenomenology and scale hierarchies
Meeting room 3, Kenkyu honkan 1F
I will discuss the problem of scale hierarchies in string phenomenology of particle physics and cosmology and propose ways to address it. In particular I will present a mechanism for supersymmetry breaking in the presence of a tiny (tunable) positive cosmological constant and describe its phenomenological consequences
Ryosuke Sato, Weizmann Inst.
Spherical symmetry of the bounce solution
Meeting room 3, Kenkyu honkan 1F
In his 1977 paper on vacuum decay in field theory: The Fate of the False Vacuum, Coleman considered the problem of a single scalar field and assumed that the minimum action tunnelling field configuration, the bounce, is invariant under O(4) rotations in Euclidean space. A proof of the O(4) invariance of the bounce was provided later by Coleman, Glaser, and Martin (CGM), who extended the proof to N > 2 Euclidean dimensions but, again, restricted non-trivially to a single scalar field. As far as we know a proof of O(N) invariance of the bounce for the tunnelling problem with multiple scalar fields has not been reported, even though it was assumed in many works since, being of phenomenological interest. We make progress towards closing this gap. Following CGM we define the reduced problem of finding a field configuration minimizing the kinetic energy at fixed potential energy. Given a solution of the reduced problem, the minimum action bounce can always be obtained from it by means of a scale transformation. We show that if a solution of the reduced problem exists, then it and the minimum action bounce derived from it are indeed O(N) symmetric.
Takahiro Terada, KIAS
Non-thermal Gravitino Production after Large-Field Inflation
Meeting room 1, Kenkyu honkan 1F
