A generic prediction of inflation is the generation of stochastic primordial gravitational waves (GWs). In the standard picture, the resulting GW spectrum is too weak to be detectable in the near future by upcoming experiments such as LISA or advanced LIGO. This is not so in the context of quintessential inflation, as the spectrum for the modes re-entering the horizon during the period of...
In this talk, I will discuss how quantum gravity effects, manifested through the breaking of discrete symmetry responsible for both Dark Matter and Domain Walls, can have observational effects through CMB observations and gravitational waves. To illustrate this idea, I will propose a simple model with two scalar fields and two Z_2 symmetries, one being responsible for Dark Matter stability,...
Primordial black holes (PBHs) may form in the early universe, and could have relevance to cosmic evolution, particularly as a dark matter candidate. Forming PBHs requires increased power on small scales, corresponding to some kind of feature in the inflaton potential. I will present a study of the fine-tuning of PBH formation for four representative inflation models, discussing the different...
This presentation introduces a cosmological model featuring a spectator field and investigates its connection to the formation of primordial black holes (PBHs) and dark matter. By considering fluctuations during inflation, we uncover a natural PBH formation process that doesn't rely on exotic physics in the potential and the fine-tuning issue can be avoided. Observational constraints...
The possibility that density fluctuations are enhanced on small scales compared to cosmological scales is central is today's cosmology, as they can seed a sizeable amount of stochastic gravitational wave backgrounds and primordial black holes (PBH). Most predictions for such scenarios are made at tree-level in perturbation theory, although loop effects are expected to be important. In this...
Single-field models of inflation that feature a non-attractor phase might lead to enhanced scalar fluctuation on scales much smaller than those seeding large-scale structure formation. In this scenario, it is possible that the spike of power at high wavenumber might spoil the successful predictions of a nearly Gaussian, scale-invariant power on large scales, e.g. in the form of loop...
How small-scale enhanced scalar fluctuations influence large scales, for instance, the one probed by the CMB, has recently been the object of an intense debate. In this context, I will first show that one-loop corrections to the large-scale power spectrum from small-scale modes in non-slow-roll dynamics are always negligible, namely they are volume suppressed by the ratio of the short to long...
Most of the elementary particles discovered in the past century have Compton wavelengths that are much smaller than the size of the atom, and, therefore, they cannot mediate any long-range forces between atoms. This changes in the early Universe, when the horizon size is small. The forces that mediate attractive interactions between particles, such as Yukawa forces, are of particular interest...
Cosmological first-order phase transitions (1stOPTs) are said to be strongly supercooled when the universe undergoes a vacuum-domination stage ended by percolation. The statistical variations in bubble nucleation histories imply that distinct causal patches percolate at slightly different times. Patches which percolate the latest undergo the longest vacuum-domination stage and as a consequence...
We study the effect of an ultra-light primordial black hole (PBH) dominated phase on the
gravitational wave (GW) spectrum generated by a cosmic string (CS) network formed as a result
of a high-scale U(1) symmetry breaking. A PBH-dominated phase leads to tilts in the spectrum
via entropy dilution and generates a new GW spectrum from PBH density fluctuations, detectable
at ongoing and...
The conventional post-inflationary reheating phase is commonly attributed to the decay of coherently oscillating inflaton into radiation. In this talk I address novel perspectives on reheating and dark matter production after inflation, considering the intricate interplay between primordial black holes (PBHs) and inflaton dynamics.
Gravitational waves (GW) in the GHz band might be observed in the near future thanks to microwave cavities. In this work, we focus on GW sourced by hyperbolic encouters of black holes and take the GraHal experiment as a benchmark. We investigate in details the set of orbital conditions leading to a fixed emission frequency, analyze the typical time window of GW production and show how to...
At the theoretical level, binary systems of evaporating primordial black holes (PBHs) are interesting situations in which the classical general relativistic dynamics related to the emission of gravitational waves (GWs), compete with the evolution driven by Hawking radiation. This competition is two-fold: first between the outspiralling dynamics produced by the loss of mass of the two bodies...
I will touch axion inflation and primordial GW, PBH formation in this model. In the second part I will touch induced gravitational waves and the superradiance of primordial black holes.
Coupling the inflaton to light fields during inflation leads to the former dissipating part of its energy into a thermal bath. The thermal fluctuations of this bath act as a source for inflaton perturbations, potentially enhancing the inflationary scalar power spectrum and therefore increasing the predicted abundance of primordial black holes (and the corresponding scalar-induced gravitational...
In this talk, I am going to present our recent work where we derive a characteristic three-peaked GW signal within the framework of no-scale Supergravity, which arises as a low energy limit of supertstring theory. We concentrate on the primordial gravitational wave (GW) spectrum induced due to second-order gravitational interactions by inflationary curvature perturbations as well as by...
I will discuss the possibility of producing a significant fraction of dark matter in the form of primordial black holes (PBHs) in the context of the pre-big bang scenario. To this purpose, I consider the enhancement of curvature perturbations possibly induced by a variation of the sound-speed parameter c_s that emerges naturally due to higher-order string corrections. We describe the...
Testing the basic building blocks of General Relativity has gained a lot of interest in recent years. In this talk, we will present some recent results on the effects of explicit spacetime symmetry breaking on primordial tensor fluctuations using an effective field theory for Lorentz/CPT violation. We find that the graviton is still massless, but that the propagation speed of tensor modes is...
In my talk, I will present recent work on the formation of primordial black hole dark matter and the resultant gravitational wave signal, drawing from recent results of https://arxiv.org/pdf/2303.02168.pdf, https://arxiv.org/pdf/2205.04471.pdf (with co-authors W. Qin, S. Balaji, D.I. Kaiser, and E. McDonough), as well as ongoing research.
In our work, we performed a Markov Chain Monte Carlo...
