Cosmology

I will discuss symmetries that arise at the infrared fixed point of the RG flow of Einstein gravity, including conformal vs. scale invariance in various dimensions, as well as 1-form generalized global symmetries and new anomalies that arise among them.

Zoom link:  https://pitp.zoom.us/j/93217255461?pwd=MXdzWDdVbWZrQzQ5UmVYVkx3US8zZz09

Primordial black holes (PBHs), if they exist, may shed light on long-standing questions on the nature
of dark matter and mechanism driving cosmic inflation. If we associate their origin to the presence of enhanced primordial scalar fluctuations generated during inflation, the underlying dynamics that populates these objects can also provide distinctive sources of gravitational waves (GWs), potentially detectable with current or forthcoming GW experiments. Therefore, their population, along with the associated GW signal offer promising opportunities to shed light on the nature of inflation, by opening up a unique window to its dynamics at scales inaccessible by conventional CMB probes. In this talk, I will review some of the compelling inflationary scenarios able to trigger the formation of such objects in the post-inflationary universe by enhancing the amplitude of the primordial scalar perturbations. In this context, I will discuss single and multi-field realizations with a focus on theoretical aspects of model building, discussing common themes shared among models in conjunction with their distinctive phenomenological implications in the form of a primordial GW background.

Zoom Link: https://pitp.zoom.us/j/98857635213?pwd=UGZoMXY4TnJBSmc1RlUvbGprSWlRQT09

Cosmology presents some puzzling aspects: the cosmological constant, the nature of the big bang, the source of inflation, and perhaps the tension in Hubble constant values. One normally uses standard effective field theory to study cosmology. But we know that such an approach fails in black holes due to the information paradox. We will draw on lessons on black holes to see how quantum gravity effects can modify evolution on macroscopic scales, and that such effects may be important is resolving puzzles in cosmology.

Zoom link:  https://pitp.zoom.us/j/98085421952?pwd=NFBCWXNBNkhrTVpaRkRlOWRtSkczdz09

EMRIs are one of the primary targets of spaceborne gravitational wave (GW) detectors and will be ideal GW sources for testing fundamental laws of gravity. In a generic non-Kerr spacetime,  the EMRI system  is non-integrable due to the lack of the Carter constant. As a result,  chaos along with resonance islands arise in these systems leaving a non-Kerr signature in the EMRI waveform as proposed in many previous studies. In this work, we systematically analyze the dynamics of an EMRI system near orbital resonances and we have derived an effective resonant Hamiltonian that describes the dynamics of the resonant degree of freedom  with the action-angle formalism. We have two major findings: (1) the chaotic orbits in general produce unique commensurate jumps in actions and (2) the EMRI orbits driven by radiation-reaction in general do not cross the resonance islands.

Zoom Link: https://pitp.zoom.us/j/95975225333?pwd=V05NZzQ3cE9neUZpN3RIOCt0UE5mZz09