2010-07-09

Joint Seminar

14:30-16:00 Jonathan Ganc (UT Austin)

Title: A new method for calculating the primordial bispectrum in the squeezed limit.

Abstract: In 2003, Creminelli and Zaldarriaga proposed a consistency relation for the primordial curvature perturbation of all single-field inflation models; it related the bispectrum in the squeezed limit to the spectral tilt. Notably, their result is produced via classical arguments whereas most bispectrum calculations use quantum field theory (via the in-in formalism, for example). We have applied similar arguments to calculate the squeezed-limit primordial bispectrum using the in-in formalism and have arrived at a generic formula that doesn't rely on a slow-roll approximation. We were not able to verify the consistency relation in all generality, though it should be able to be demonstrated by our technique if it does, in fact, hold in general; we did explicitly verify it for slow-roll inflation (a known result) and for power-law inflation. Our technique could also be useful for calculating the single-field trispectrum in the squeezed limit and could be adapted for certain types of multi-field inflation models.

16:30-18:00 Norihiro Tanahashi (YITP, Kyoto)

Title: Extradimension detection by gravitational wave observations

Abstract:
Inspired by the gauge/gravity correspondence, it was conjectured for
the RS-II braneworld model, which is composed of five-dimensional AdS
bulk spacetime and a four-dimensional brane in it, that the
five-dimensional classical gravity in the bulk spacetime is equivalent
to some four-dimensional quantum field theory coupled to gravity on
the brane. In this scenario, the Hawking radiation from a
four-dimensional black hole is largely enhanced due to existence of
the new quantum fields, and the enhancement factor is related to the
extradimension scale. We would like to discuss observational
consequences of this scenario, especially focusing on gravitational
wave observations. Black hole binaries are typical targets for the
gravitational wave detectors, and those binaries will lose their
energy and angular momentum due to the enhanced Hawking radiation.
This effect will be detectable if the enhancement factor, i.e., the
extradimension scale, is sufficiently large. Observations of this
effect may give a new constraints on the extradimension scale. In the
presentation, we will introduce constraints on the extradimension
scale by observations of LISA which was given by McWilliams
(arXiv:0912.4744) recently, and discuss further constraints from BH/BH
or NS/BH binary observations by DECIGO.