2017-05-01

UTAPwiki/セミナー/初期宇宙・相対論速報
Speaker: Takahiro Hayashinaka (RESCEU)
Title: Negativity of electromagnetic response in de Sitter space
Abstract:
This talk will be dedicated to show recent activities on the topic. In the first half of the talk, I explain how negative, i.e. unstable, electromagnetic responses have been revealed. Though this phenomenon was repeatedly reported by several groups recently [1], neither physical origin or intellectual interpretation of the phenomenon have been explicitly given up to the present.
The rest of my talk involve this point. Inspired by a relevant negative response phenomenon in a specific ferroelectric matter [2], I recognized importance of spontaneous symmetry breaking and the effective action or potential of the system. A variation of renormalization group technique, which is called non-perturbative renormalization group (NPRG) [3], can be used for evaluation of the effective action. I re-developed a gauge-invariant formulation of flow equation for scalar QED effective action in curved spacetime. In this formalism, one introduces an IR cutoff scale. As a result, undesirable behavior of the IR modes in de Sitter spacetime can be virtually suppressed [4]. The solution for the flow equation has not been found yet though, I will explain about construction of the gauge-invariant flow equation.
References:
[1] 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, T. Hayashinaka, T. Fujita and J. Yokoyama, JCAP 1607 (2016) 07 010
[2] G. Catalan et al., Nature matt. (2015) 14, 137, S. Kasamatsu et al., Adv. Mater. 2016, 28, 335-340
[3] Christof Wetterich. Phys. Lett., B301:90-94 (1993), M. Reuter and C. Wetterich. Nucl. Phys., B417:181-214 (1994)
[4] For recent application of NPRG in cosmology, see: Maxime Guilleux, Theses, Universite paris Diderot, September, 2016