Davide Racco

Last Name

Racco

First Name

Davide

ORCID

0000-0002-0859-8751

Organisational unit

09737 - Senatore, Leonardo / Senatore, Leonardo

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Publications 1 - 10 of 12

Neutrino masses from large-scale structures: future sensitivity and theory dependence
Racco, Davide; Zhang, Pierre; Zheng, Henry (2024)
arXiv
In the incoming years, cosmological surveys aim at measuring the sum of neutrino masses $Σm_ν$, complementing the determination of their mass ordering from laboratory experiments. In order to assess the full potential of large-scale structures (LSS), we employ state-of-the-art predictions from the effective field theory of LSS (EFTofLSS) at one loop to perform Fisher forecasts on the sensitivity (combining power spectrum and bispectrum) of ongoing and future surveys (DESI, MegaMapper) in combination with CMB measurements (Planck, Litebird and Stage-4). We find that the 1$σ$ sensitivity on $Σm_ν$ is expected to be 15 meV with Planck+DESI, and 7 meV with S4+MegaMapper, where $\sim 10\%$ and $30\%$ of the constraints are brought by the one-loop bispectrum respectively. To understand how robust are these bounds, we explore how they are relaxed when considering extensions to the standard model, dubbed `new physics'. We find that the shift induced on $Σm_ν$ by a $1σ$ shift on new physics parameters (we consider extra relativistic species, neutrino self-interactions, curvature or a time-evolving electron mass) could be $\mathcal O(10)$ meV for Planck+DESI, but it will be suppressed down to $\mathcal O(1)$ meV in S4+MegaMapper. Our study highlights the quantitative impact of including the bispectrum at one loop in the EFTofLSS, and the robustness of the sensitivity to $Σm_ν$ against potential new physics thanks to the synergy of cosmological probes.
Impact of Supercooling on Direct Searches for Dark Matter and Gravitational Wave Backgrounds
Racco, Davide; Stanzione, Alfredo (2025)
arXiv
An interesting feature of a cosmological phase transition can be a stage of exponential expansion (supercooling). The modified expansion history and the entropy injection at reheating, can affect the final energy fraction of dark matter. In this paper, we revisit the calculation of the freeze-out and freeze-in dynamics, showing additional effects on top of the standard dilution factor if the dark matter production is completed during the supercooling stage. We show for the first time how these effects can be particularly interesting for direct detection, as the parameter space for WIMP-like candidates shifts from excluded to allowed regions, and freeze-in candidates get closer to experimental reach. A phenomenological motivation to consider supercooling is the associated gravitational wave background. The implications of a finite-duration reheating stage, when the equation of state is close to matter-domination, are a peculiar low-frequency spectrum, and its shift to lower frequencies. These effects are a complementary test of the dynamics that we study for dark matter production, and remarkably can link direct detection of dark matter and gravitational wave astronomy.
Reconstructing Primordial Curvature Perturbations via Scalar-Induced Gravitational Waves with LISA
Jonas El Gammal; Aya Ghaleb; Gabriele Franciolini; et al. (2025)
Journal of Cosmology and Astroparticle Physics
Many early universe scenarios predict an enhancement of scalar perturbations at scales currently unconstrained by cosmological probes. These perturbations source gravitational waves (GWs) at second order in perturbation theory, leading to a scalar-induced gravitational wave (SIGW) background. The LISA detector, sensitive to mHz GWs, will be able to constrain curvature perturbations in a new window corresponding to scales $k \in [10^{10}, 10^{14}] \,{\rm Mpc}^{-1}$, difficult to probe otherwise. In this work, we forecast the capabilities of LISA to constrain the source of SIGWs using different approaches: i) agnostic, where the spectrum of curvature perturbations is binned in frequency space; ii) template-based, modeling the curvature power spectrum based on motivated classes of models; iii) ab initio, starting from first-principles model of inflation featuring an ultra-slow roll phase. We compare the strengths and weaknesses of each approach. We also discuss the impact on the SIGW spectrum of non-standard thermal histories affecting the kernels of SIGW emission and non-Gaussianity in the statistics of the curvature perturbations. Finally, we propose simple tests to assess whether the signal is compatible with the SIGW hypothesis. The pipeline used is built into the SIGWAY code.
Revisiting Isocurvature Bounds on the Minimal QCD Axion
Graham, Peter W.; Racco, Davide (2025)
arXiv
The QCD axion has important connections to early universe cosmology. For example, it is often said that isocurvature limits rule out a combination of high axion decay constant, f_a, and high inflationary Hubble scale, H_I. High scales are theoretically motivated, so it is important to ask how robust this constraint is. We demonstrate that this constraint is naturally evaded when the quartic coupling of the complex U(1)_PQ-breaking field is small (e.g. ≲ 10^-6). In this case, f_a changes from a larger value during inflation to a smaller value in the later universe, suppressing isocurvature perturbations. Importantly, we show that in large parts of parameter space this solution is not jeopardised by overproduction of the axion through parametric resonance. The isocurvature bounds are thus dependent on UV physics. We have found that, even for the minimal QCD axion, large parts of UV parameter space at both high f_a and high H_I are in fact allowed, not ruled out by isocurvature constraints.
Revisiting isocurvature bounds on the minimal QCD axion
Graham, Peter W.; Racco, Davide (2025)
Journal of High Energy Physics
The QCD axion has important connections to early universe cosmology. For example, it is often said that isocurvature limits rule out a combination of high axion decay constant, f_a, and high inflationary Hubble scale, H_I. High scales are theoretically motivated, so it is important to ask how robust this constraint is. We demonstrate that this constraint is naturally evaded when the quartic coupling of the complex U(1)_PQ-breaking field is small (e.g. ≲ 10⁻⁶). In this case, f_a changes from a larger value during inflation to a smaller value in the later universe, suppressing isocurvature perturbations. Importantly, we show that in large parts of parameter space this solution is not jeopardised by overproduction of the axion through parametric resonance. The isocurvature bounds are thus dependent on UV physics. We have found that, even for the minimal QCD axion, large parts of UV parameter space at both high f_a and high H_I are in fact allowed, not ruled out by isocurvature constraints.
Footprints of the QCD Crossover on Cosmological Gravitational Waves at Pulsar Timing Arrays
Franciolini, Gabriele; Racco, Davide; Rompineve, Fabrizio (2024)
Physical Review Letters
Pulsar timing arrays (PTAs) have reported evidence for a stochastic gravitational wave (GW) background at nanohertz frequencies, possibly originating in the early Universe. We show that the spectral shape of the low-frequency (causality) tail of GW signals sourced at temperatures around T ≳ 1 GeV is distinctively affected by confinement of strong interactions (QCD), due to the corresponding sharp decrease in the number of relativistic species, and significantly deviates from ∼f³ commonly adopted in the literature. Bayesian analyses in the NANOGrav 15 years and the previous international PTA datasets reveal a significant improvement in the fit with respect to cubic power-law spectra, previously employed for the causality tail. While no conclusion on the nature of the signal can be drawn at the moment, our results show that the inclusion of standard model effects on cosmological GWs can have a decisive impact on model selection.
Reconstructing primordial curvature perturbations via scalar-induced gravitational waves with LISA
El Gammal, Jonas; Ghaleb, Aya; Franciolini, Gabriele; et al. (2025)
Journal of Cosmology and Astroparticle Physics
Many early universe scenarios predict an enhancement of scalar perturbations at scales currently unconstrained by cosmological probes. These perturbations source gravitational waves (GWs) at second order in perturbation theory, leading to a scalar-induced gravitational wave (SIGW) background. The LISA detector, sensitive to mHz GWs, will be able to constrain curvature perturbations in a new window corresponding to scales k ∈ [10$^{10}$, 10$^{14}$] Mpc$^{-1}$, difficult to probe otherwise. In this work, we forecast the capabilities of LISA to constrain the source of SIGWs using different approaches: i) agnostic, where the spectrum of curvature perturbations is binned in frequency space; ii) template-based, modeling the curvature power spectrum based on motivated classes of models; iii) ab initio, starting from first-principles model of inflation featuring an ultra-slow roll phase. We compare the strengths and weaknesses of each approach. We also discuss the impact on the SIGW spectrum of non-standard thermal histories affecting the kernels of SIGW emission and non-Gaussianity in the statistics of the curvature perturbations. Finally, we propose simple tests to assess whether the signal is compatible with the SIGW hypothesis. The pipeline used is built into the SIGWAY code.
Understanding the Nature of Scalar-Induced Gravitational Waves
A. J. Iovino; G. Perna; D. Perrone; et al. (2025)
We offer a physical interpretation of the origin of the scalar-induced gravitational wave background, showing that it is mainly produced around the peaks of the scalar perturbations. We also provide a compact expression to estimate the amount of scalar-induced gravitational waves generated by peaks.
Probing Flavour Deconstruction via Primordial Gravitational Waves
Fabri, Noemi; Isidori, Gino; Racco, Davide; et al. (2025)
arXiv
We study the production of primordial gravitational waves (GWs) from first-order phase transitions (FOPTs) in extensions of the Standard Model based on Flavour Deconstruction (FD). The link fields inherent to FD generically form a rich scalar sector, with sizeable couplings at the TeV scale, providing natural conditions for strong FOPTs and correspondingly large GW emission. We identify the key parameters controlling the GW spectrum and enabling its detection at future GW observatories. In particular, we find that while FD scenarios can yield detectable signals, the resulting spectra typically peak at higher frequencies than the millihertz range. As a consequence, a positive observation at LISA is possible but not guaranteed, while the signal falls in the range of mid-band proposals, making FD models an intriguing target for upcoming GW searches.
Neutrino masses from large-scale structures: Future sensitivity and theory dependence
Racco, Davide; Zhang, Pierre; Zheng, Henry (2025)
Physics of the Dark Universe
In the incoming years, cosmological surveys aim at measuring the sum of neutrino masses Σmν, complementing the determination of their mass ordering from laboratory experiments. In order to assess the full potential of large-scale structures (LSS), we employ state-of-the-art predictions from the effective field theory of LSS (EFTofLSS) at one loop to perform Fisher forecasts on the sensitivity (combining power spectrum and bispectrum) of ongoing and future surveys (DESI, MegaMapper) in combination with CMB measurements (Planck, Litebird and Stage-4). We find that the 1σ sensitivity on Σmν is expected to be 15 meV with Planck+DESI, and 7 meV with S4+MegaMapper, where ∼10% and 30% of the constraints are brought by the one-loop bispectrum respectively. To understand how robust are these bounds, we explore how they are relaxed when considering extensions to the standard model, dubbed ‘new physics’. We find that the shift induced on Σmν by a 1σ shift on new physics parameters (we consider extra relativistic species, neutrino self-interactions, curvature or a time-evolving electron mass) could be O(10) meV for Planck+DESI, but it will be suppressed down to O(1) meV in S4+MegaMapper. Our study highlights the quantitative impact of including the bispectrum at one loop in the EFTofLSS, and the robustness of the sensitivity to Σmν against potential new physics thanks to the synergy of cosmological probes.

Publications 1 - 10 of 12

Davide Racco

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