19 APR 2021
16:00 - 18:00

Theory of Conflictless Drama in Soviet Literature


https://www.skyroom.online/ch/ipmseminars/ipm-seminars-2021

User: biweeklyseminars
Pass: biweeklyseminars

20 APR 2021
15:00 - 16:00

Abstract:

The LIGO discovery of the gravitational waves from merging of the binary of black holes (BH) has revitalized interests in the primordial black holes (PBH) as the dark matter candidates. One of the mechanism of generation of these PBHs is the collapse of large overdensities during radiation dominated phase. Inflation is a prime candidate for generation of density perturbations. However the typical magnitude of fluctuation generated during inflation at the CMB scales is very small. In the first part of this talk I will describe a mechanism for generation of such large amplitude fluctuations during inflation. The mechanism is based on the formalism of Extended EFT of inflation (EEFToI) with the sixth order polynomial dispersion relation for scalar perturbations. The instability mechanism needs to be arranged to kick in at the scales of interest which is related to the mass of the PBHs one would like to produce. In the second part of the talk, I will focus on another mechanism of PBH formation during inflation, namely the nucleation of domain walls during inflation. I explicitly construct a double field inflationary model, which satisfies the latest PLANCK constraints at the CMB scales and produces the whole dark matter energy density as primordial black holes (PBHs), in the mass range 10^{-17}-10^{-13} solar mass. Obtaining PBHs in this mass range enforces the scale of inflation to be extremely low, which makes the efforts to observe gravitational waves at the CMB scales futile. However, it is high enough to allow for a successful Big Bang Nucleosynthesis (BBN). Instead, exit from the rolling metastable direction to the true vacuum of the potential may happen with a first-order phase transition (PT) that leaves behind a stochastic gravitational wave background (SGWB), which is potentially observable by LISA. We show that PBHs produced during such a first-order PT from the collision of bubble walls contribute negligibly to the PBH mass spectrum. Examining the mass distribution of PBHs and possible SGWB from the end of inflation, we may be able to gain invaluable information about the topography of the landscape in our neighborhood.




Date: Tuesday, April 20th

3 p.m. - 4 p.m. (Tehran time)

Unusual time



Zoom. (click)

Meeting ID: 884 3079 2016

Passcode: 395721

21 APR 2021
13:30 - 15:00

Abstract
The XENON1T collaboration recently reported the excess of events from recoil electrons which may be sign of a fundamental new discovery about our universe. In this talk, I will review the current status of different dark matter (DM) direct detection experiments towards ultimate DM detector. I will show that sterile neutrinos with masses around 90 keV and specific effective coupling can explain the XENON1T anomaly preserving DM astrophysical and cosmological constraints, and it possibly describes the anomalies in other experiments. At the end I will try to explain how one can be convinced that DM has been discovered or not from observing an unexplained excess?
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