Departures from General Relativity impact the propagation of gravitational waves (GW) in multiple ways. I’ll explain the theoretical underpinnings of these phenomena, and how they connect to potentially observable features of waveforms. I’ll review the current status of constraints on modified GW propagation, and outline how LISA and other detectors are expected to enhance these bounds.

I will review the stochastic gravitational wave backgrounds produced by cosmological phase transitions and cosmic strings.

We present recent results on predictions of LISA's ability to determine cosmic string model parameters. These predictions are made using SGWBinner to fit an injected signal for a variety of cosmic string templates (to be discussed in a complementary talk). We find that LISA should be able to accurately and precisely recover the parameters of simple field-theoretic string models in standard...

In this talk, I will report on the progress of the cosmic string parameter estimation project and on its contribution to building up the LISA catalogue of templates for cosmic strings.

The stochastic gravitational wave background (SGWB) produced at the electroweak phase transition is expected to be peaking within LISA's sensitivity frequency range, being a promising test of high energy physics and beyond Standard Model extensions. The contribution of magnetohydrodynamic (MHD) turbulence to the cosmological SGWB is one of the least understood sources due to the necessity, in...

In this project, we explore the reconstruction of stochastic gravitational wave backgrounds generated by cosmological phase transitions using LISA, taking into account signals from bubble collisions, sound waves and turbulence. We implement the corresponding signal templates in terms of the both the geometric parameters related to the spectral shape, as well as in terms of the thermodynamical...

We give a detailed review of the theory and observations of Primordial Black Holes and specialize on the prospects for detection with the LISA mission.

I will present the status of the development of the PrimBHoles code. The code implements various models of PBH formation based on the most recent theoretical prescriptions, as well as their merger rates, stochastic backgrounds (2nd order, from binaries, etc), and other gravitational-wave signatures.

The 3rd observing run of Advanced LIGO, Virgo and KAGRA (LVK) increased the number of confident gravitational-wave detections from compact binary coalescences to 90. This includes the second ever binary neutron star merger to be detected, and a small number of neutron star-black hole mergers - the first of their kind to be seen by the LVK. However, none of these events were observed with a...

The future space-based gravitational-wave detector LISA will deliver rich, information-dense data by listening to the milliHertz universe. The measured time series will contain the imprint of tens of thousands of detectable astrophysical sources, emitting continuous, transient and stochastic signals. Finding and characterising all the resolvable sources is a vast and unsolved task. Detecting a...

Gravitational lensing is an unavoidable phenomenon in which the propagation path of gravitational waves changes due to the presence of structures along the line of sight. In this talk, I will give an overview of the lensing signatures relevant for LISA.

Early Universe dynamics beyond the standard single-field slow-roll paradigm may produce a Stochastic Gravitational Wave Background (SGWB) in the LISA band. We adopt a recently developed data analysis pipeline to forecast the constraints on the model parameters and discuss the implications of our forecast for inflationary model builders.

I will discuss the current Cosmology Working Group effort to initiate the first LISA template databank for SGWB signals sourced by inflationary models.

In this talk, we will explore some of the challenges and possibilities of detecting stochastic gravitational wave backgrounds (SGWBs) with LISA. The main scientific observables produced by LISA will be three semi-independent TDI data streams, one of which is a so-called null channel, which has reduced sensitivity to gravitational waves (GW). LISA will certainly have the ability to directly...

We explore the impact of choosing different sets of Time-Delay Interferometry

(TDI) variables for detecting and reconstructing Stochastic Gravitational Wave

Background (SGWB) signals and estimating the instrumental noise in LISA. Most

works in the literature build their data analysis pipelines relying on a

particular set of TDI channels, the so-called AET variables, which are

orthogonal...

LISA, the first space-based gravitational wave observatory designed for detecting gravitational waves in the mHz frequency range, is expected to operate in a regime where gravitational wave signals continuously dominate the instrumental noise. This poses a technical challenge of accurately quantifying and understanding the instrumental noise in the presence of gravitational waves, which is...

Primordial stochastic gravitational wave backgrounds in the LISA band could have been generated from cosmic inflation, an early phase transition, or a myriad of other dynamic processes. Any detection would almost certainly provide the earliest constraints on cosmology. But the rich science potential of these signals does not come for free: LISA's band will be signal-dominated at all times. The...

Crucial aspects of LISA data analysis regard our ability to distinguish the various signals and signatures the LISA data will contain. In particular, signals of stochastic nature will be particularly challenging to sort out, as they could be of instrumental, galactic, astrophysical or cosmological origins, lacking of unique signature to identify them. To tackle this issue, efforts have been...

While a first-order phase transition at the electroweak scale is not expected within the Standard Model, these occur in many BSM scenarios. Therefore, detecting a stochastic gravitational wave background consistent with a first-order phase transition could point to new physics, while a null detection could constrain or even exclude many BSM models. However, recovering the physical parameters...

Extreme mass ratio inspirals (EMRIs) are among the primary targets for the Laser Interferometer Space Antenna (LISA). The extreme mass ratios of these systems result in relatively weak GW signals, that can be individually resolved only for cosmologically nearby sources (up to $z\approx2$). The incoherent piling up of the signal emitted by unresolved EMRIs generate a confusion noise, that can...

I will first quickly review the mechanism for primordial gravitational wave (GW) generation in axion-inflation models coupled with a gauge sector via a Chern-Simons term. I will then specialise to the case of an SU(2) sector in a setup where the inflaton is non-minimally coupled to gravity and detail on the gravitational wave spectrum at small scales, those of interest for GW interferometers.

If Primordial Black Holes (PBHs) are formed due to an enhanced scalar-perturbation amplitude at small scales, their formation is inevitably accompanied by the generation of gravitational waves (GWs). Thanks to a coincidence of scales, LISA will be able to observe the GWs associated with the formation of asteroidal mass PBHs, which may constitute the entirety of the dark matter. We will review...

Excellent progress has been made in developing high-level modelling of the gravitational wave power spectrum from early universe phase transitions. This progress has been made possible in part by large-scale simulations of bubble collisions. However, challenges remain, particularly in understanding and modelling the development of nonlinearities, including shocks and turbulence, which become...

We will discuss how gravitational wave astronomy can probe various primordial black hole (PBH) scenarios. This includes gravitational waves originating from coalescing PBH binaries in the late universe or from PBH formation in the early universe. These channels can be accessed by LISA if PBHs occupy the (sub)solar or the asteroid mass range, respectively.

In this talk we discuss, as recently proposed in [arXiv:2303.10718 [astro-ph.CO]][1], how chromo-natural inflation (CNI) can be made compatible with observations at CMB scales through the introduction of a non-minimal coupling of the axion-inflaton kinetic term with the Einstein tensor. The resulting gravitationally-enhanced friction allows the gauge friction to be reduced just enough to...

A thermal plasma necessarily generates a spectrum of gravitational waves that is, however, too weak to be measurable unless the maximum temperature of the system is large. We present a mechanism ensuring a high dark-sector temperature as a result of reheating dynamics. As an example, we consider axion inflation coupled to a non-Abelian dark sector and we calculate the maximum temperature as a...

The gravitational wave signal produced by a cosmological phase transition depends strongly on the rate of bubble nucleation. This determines the size of bubbles at collision, and consequently affects both the peak frequency and amplitude of the gravitational wave signal. Making reliable predictions of the nucleation rate is made difficult by its spacetime dependence, and by non-equilibrium...

We use a full general relativistic framework to study the self-similar expansion of bubbles of the stable phase in a first order phase transition in the early universe. Self-similarity requires a near-conformal equation of state in both phases, where the ratio between the energy density and pressure of the fluid is constant but different in the two phases. The Israel junction conditions at the...

Based on the recent article [2023.02399], we discuss the LISA potential for finding evidence of New Physics from measurements of the Stochastic GW Background (SGWB). As a benchmark scenario, we study a version of the low-scale Majoron model equipped with lepton number symmetry and an inverse seesaw mechanism for neutrino mass generation. In particular, we discuss under which circumstances the...

In this talk, I will present a few examples on how collider searches for New Physics may be correlated with a future observation of primordial gravitational waves. One such example concerns the recently observed anomaly in W-boson mass by CDF, and another one elaborates on trilinear Higgs coupling constraints and their impact on the strength of the electroweak phase transition.

I will present the parametric resonance excitation of an electromagnetic field by a gravitational wave. The former is exponentially amplified, while the latter is damped. This mechanism takes place in the framework of Einstein gravity and might happen in different configurations. In a medium with the speed of light smaller than 1, in natural units, the conversion might happen in the first...

Large scale primordial magnetic fields (PMFs) threading the intergalactic medium are observed ubiquitously in the Universe playing a key role in the cosmic evolution while their origin constitutes one of the long-standing issues in cosmology. In the present talk, we propose a novel natural ab initio mechanism for the origin of such PMFs through the portal of supermassive primordial black holes...