- Astronomy Unit home
- The Astronomy Unit
- News
- Research
- Events
- Teaching
- MSc Astrophysics
- MSc Astrophysics Projects
- MSc Physics (EuroMasters)
- PG Certificate in Astronomy and Astrophysics
- QM Astronomical Observatory
- Telescopes
- Astronomy Unit PhD Programme
- How to Apply
- Available Projects
- Astrometry of Saturn's satellites
- Disc-planet interactions in non-isothermal discs
- Dust-gas interactions and the signatures of planets in discs
- Geometric Algebra in Astrophysics
- Interrogating the dynamics of conjugated polymers using neutron scattering and molecular dynamics
- New generation of ultra-stable instruments for exoplanet studies
- Planet formation by gravitational instabilities
- Relativistic cosmology in the era of large scale surveys
- Topological Fluid Dynamics

- Postgraduate Taught Astrophysics Modules

- Group Members

# Hemispherical power asymmetry from a scale dependent bispectrum - Donough Regan

## 18 November 2015

Time: 4:30pmVenue: See Talk Details

Series:

The London Relativity and Cosmology Seminar

Speaker:

Donough Regan (Sussex)

Abstract:

The hemispherical power asymmetry is regarded as one of (perhaps three) unsolved anomalies of CMB detections to date. Many explanations have been proposed, with most, from an inflationary setting, involving a single high amplitude large-scale mode. For a sufficiently large primordial bispectrum this exceptional mode can explain the asymmetry. Or so the story goes…

In this talk I will discuss an extension of previous calculations clarifying that in the multi-source case, that the key quantity is not the reduced bispectrum but rather a ‘response function’ (only agreeing with the reduced bispectrum in the single source limit). Our extension will include the effect of scale dependency which has often been ignored, but which is observed in the actual power asymmetry.

Having gone through this ‘clarification’ I will then describe why it is so difficult to construct a successful realisation, which has small enough bispectrum amplitude, but large enough power asymmetry. This will be in the form of a no-go theorem with several assumptions.

But don’t worry all is not lost. I will then describe a working example (where we break one of the above assumptions!). This model, which is not at all physical (or motivated or in any way endorsed) will be shown to satisfy all observational constraints.