I will present an overview of recent developments in using gravitational wave experiments to probe the physics of inflation, with a focus on how gravitational wave signals can test fundamental aspects of early-universe cosmology.
In multi-field inflationary models, couplings between fields are not limited to the potential of the model, but can also be present in kinetic terms. In such a case, they can be interpreted as a non-trivial structure of the space of fields. Non-vanishing curvature of this space can lead, if negative, to a new phenomenon called geometrical destabilization.
α-attractors are a very promising...
We explore the production of gravitational waves resulting from a first-order phase transition (FOPT) in a non-minimally coupled "Dark Higgs Inflation" model. Utilizing a single scalar field both as the inflaton and as the Dark Higgs breaking the gauge symmetry in the dark sector, we demonstrate the feasibility of a unified framework for inflation and observable gravitational waves from a FOPT.
We study stochastic gravitational waves (GW) sourced by a Higgs-like spectator field via the modulated reheating mechanism. The curvature perturbations generated by the spectator in de Sitter vacuum are blue-tilted and strongly non-Gaussian. They must be suppressed on scales probed by the CMB anisotropies but can grow large on sub-Mpc scales, generating observationally testable stochastic GWs....
LISA and ET will operate in different frequency ranges but with comparable integrated sensitivities to a stochastic GW background (SGWB). We explore their synergies in detecting cosmological SGWBs with large amplitudes and broad frequency spectra, arising from sources such as cosmological phase transitions, cosmic strings, and primordial inflation. By combining measurements from both...
-Quantum evaporation of a black hole is conventionally studied
semiclassically by assuming self-similarity of the black hole
throughout the evaporation process. However, its validity was recently
questioned, and the lifetime of a black hole is conjectured to be much
extended by the memory burden effect. It gives rise to the possibility
that the primordial black holes (PBHs) lighter than...
We investigate a novel gravitational wave (GW) production mechanism from gravitons generated during the pre-thermal phase of cosmic reheating, where the energy density is dominated by non-thermalized inflaton decay products, dubbed reheatons. We consider multiple production channels, including: $i)$ pure inflaton-inflaton annihilation, $ii)$ graviton Bremsstrahlung from inflaton decay, $iii)$...
In this talk, I will summarize some of our efforts to interpret the GWB-like signal observed by the NANOGrav collaboration as inflationary gravitational waves, by sampling reheating temperature, tensor spectral index, and the running of the tensor spectral index. I will show that there is available parameter space to describe the signal, even if we impose constraints from CMB, LVK, and do not...
Particle physics scenarios with discrete symmetries can be probed by searching for their cosmological relics. When the symmetry is spontaneously broken in the early Universe, a network of topological defects (domain walls) is formed, that generically ends up making a large fraction of the energy budget of the Universe. While these defects are required to decay away before dominating, they are...
We present the audible axion mechanism extended by a period of supercooling that delays the onset of axion oscillations. While the original setup relies on a large axion decay constant and coupling to a dark Abelian gauge field to produce sizable gravitational wave signals, in this talk we discuss how supercooling opens up the testable parameter space and reduces the required coupling to...
Simulation-Based-Inference (SBI), also known as likelihood-free inference, is an alternative approach to Montecarlo techniques to perform Bayesian inference. SBI typically relies on Machine Learning (ML) methods to approximate the posterior distribution for some model parameters given the observed data. In the past years, SBI has been applied to a range of physics problems, including...
I will review nonperturbative approaches to studying cosmological phase transitions, and what they have taught us. This includes an introduction to the methodology, a potted historical survey, and highlights of recent results.
First-order phase transitions play a pivotal role in many models of particle physics and the early Universe, and are a key target of current and future gravitational-wave observatories. However, we lack a satisfying theoretical understanding of this process, with existing approaches working only in imaginary (Euclidean) time, and relying on assumptions that have yet to be empirically tested. A...
The evidence of a Stochastic Gravitational Wave Background (SGWB) in the nHz frequency range is posed to open a new window on the Universe. A preferred explanation relies on a supercooled first order phase transition at the 100 MeV–GeV scale. We address address its feasibility going from the particle physics model to the production of the gravitational waves. We take a minimal approach for the...
We demonstrate in this work that scalar-induced gravitational waves (SIGWs) can serve as a natural and powerful probe of thermal leptogenesis occurring at extremely high scales-beyond the reach of conventional particle physics experiments. As a proof of concept, we present a simple leptogenesis model in which an early matter-dominated phase, tracking the leptogenesis scale, is responsible for...
- Gravitational waves (GWs) can be produced by a first-order phase transition in the early Universe via the fluid perturbations induced in the primordial plasma by the expansion and collision of broken-phase bubbles. I will review the production of GWs by the anisotropic stresses of velocity and magnetic fields induced in a first-order phase transition and present analytical estimates and...
Terminal velocity reached by bubble walls in cosmological first-order phase transitions is an important parameter determining both primordial gravitational wave spectrum and the production of baryon asymmetry in models of electroweak baryogenesis. In this talk I discuss the recent results for local thermal equilibrium approximation for which, using hydrodynamic simulations, we have confirmed...
We explore the dynamics of cosmological phase transitions in a dark sector model featuring a dark photon associated with a U(1)D gauge symmetry. Our analysis focuses on two complementary approaches to construct the effective potential: an scale invariant model with the Coleman-Weinberg potential, both using the high-temperature approximation and a full numerical evaluation of the thermal...
Gravitational waves (GWs) produced during a first-order phase transition are a favourite candidate as a probe of beyond the standard model physics at future space-based experiments. The spectrum of produced GWs depends strongly on the terminal velocity at which bubbles of the broken phase expand in the plasma, and in particular on whether this velocity can become ultrarelativistic.
In this...
Focusing on supercooled phase transitions in models with classical scale symmetry, we investigate the limitations of derivative expansions in constructing a thermal EFT description for bubble nucleation. We demonstrate that derivative expansions for gauge field fluctuations diverge after the two leading orders because the gauge field mass varies strongly between the high- and low-temperature...
The experimental revolution unleashed by the discovery of gravitational waves will unfold over the coming decades. To maximize the discovery potential, a theoretical understanding of quantum matter out of equilibrium is essential. Addressing this regime with conventional methods is extremely challenging. Holography, a theoretical framework originating from string theory, maps this problem to...
Among all the possible candidates for Dark Matter, one appealing example is a population of Primordial Black Holes, which could have been borne by various processes in the early stages of the Universe. In this talk, I will investigate the formation of such objects as the result of the collapse of energy density fluctuations originating from supercooled first-order phase transitions. I will...
In this talk I will discuss gravitational waves from supercooled cosmological first-order phase transitions. If such a transition is followed by inefficient reheating, the evolution history of the universe is modified by a period of early matter domination. This leaves an imprint on the predicted gravitational-wave spectra. Using Fisher analysis we show the parameter space in reach of upcoming...
Gravitational Wave Astrophysics has already demonstrated its potential to explore the Universe, but we are still at the beginning of this journey. While we regularly observe gravitational waves from compact binaries, we do not know what we may discover next. In my talk, I will give an overview of the field of Gravitational Wave Astrophysics by discussing the gravitational-wave detectors...
Detection of quasi-monochromatic, long-duration (continuous) gravitational wave radiation emitted by, e.g., asymmetric rotating neutron stars, planetary or asteroid mass - primordial BH (PBH) binaries during their in-spiral phase in our Galaxy requires a long observation time to distinguish it from the detector’s noise. If this signal is additionally microlensed by a lensing object located in...
Gravitational wave detectors offer promising probes to search for dark matter, both directly and indirectly. If dark matter originates from a background of ultralight gauge bosons, these bosons could exert forces on the test masses of gravitational wave detectors, inducing displacements with characteristic frequencies determined by the boson mass. On the indirect side, the Fermi satellite has...
Inspiralling SMBH binaries constitute a natural explanation of the gravitational wave (GW) background discovered in pulsar timing array (PTA) data. In this talk, I will present a fast semianalytical computation of the expected GW background from SMBH binaries and discuss the SMBH fit to the PTA data that shows evidence of environmental effects or binary eccentricities. I will identify...
Pulsar timing arrays (PTAs) have now revealed a nano-hertz stochastic gravitational-wave background whose amplitude and spectral shape are consistent with a cosmic population of merging super-massive black-hole (SMBH) binaries. Explaining how such binaries bridge the ``final parsec’’ separation before gravitational radiation dominates remains a key challenge. Following the mechanism proposed...
An early period of matter domination that suddenly transitions into radiation results in a striking gravitational wave signature. Assuming a given form for the initial power spectrum of curvature fluctuations, one can then do the work to distinguish different sources of early matter domination from features in the spectrum. We first do a model independent analysis where we reduce the features...
An early period of matter domination that suddenly transitions into radiation results in a striking gravitational wave signature. Assuming a given form for the initial power spectrum of curvature fluctuations, one can then do the work to distinguish different sources of early matter domination from features in the spectrum. We first do a model independent analysis where we reduce the features...
