arXiv subjects

Ofelia Pisanti

Publications and source records attributed to Ofelia Pisanti.

At least 19 recordsLinked to original sources

arXiv2026

Impact of non-standard neutrino-electron interactions on Big Bang Nucleosynthesis

Neutrino non-standard interactions (NSI) with electrons, predicted in many extended theoretical models of particle physics, are known to alter the picture of neutrino decoupling from the cosmic plasma. We update previous analyses of neutrino decoupling in the presence of NSI with electrons, extending the parameter space and assessing their impact on the primordial light-element abundances produced during Big Bang Nucleosynthesis (BBN). We show that tracking the NSI-induced modifications of the neutrino distributions is necessary to accurately predict the helium-4 abundance, which cannot be derived from a pure $N_{\rm eff}$-driven change. BBN therefore provides additional observables that are complementary to $N_{\rm eff}$. We then derive cosmological constraints on non-universal and flavour-changing NSI parameters, using different dataset combinations, and compare them with bounds from terrestrial experiments. We find that the cosmological limits are significantly less stringent than the terrestrial ones, but they provide an independent probe of neutrino interactions in the early universe.

hep-ph↗

arXiv2026

When the Environment Speaks: Quantum Signatures in Non-Attractor Inflation

We study the open quantum dynamics of the adiabatic curvature perturbation interacting with a massive entropic scalar environment during an inflationary scenario featuring a transient Ultra-Slow-Roll phase. Working within a Gaussian two-field effective Lagrangian, we employ the exact Transport Equations Method to track the full non-unitary, non-Markovian evolution of the system's covariance matrix across the SR-USR-SR transition. We find that the efficiency of decoherence is sensitive to the background kinematics at horizon crossing. Most importantly, the interaction with the environment leaves distinct observable imprints on the primordial scalar power spectrum: the characteristic interference dip preceding the USR-driven enhancement can be partially or completely erased, the growth slope modified, and oscillatory features induced near the peak. Propagated to second order, these distortions further imprint on the stochastic background of Scalar-Induced Gravitational Waves, breaking single-field predictions and yielding unique spectral signatures potentially accessible to LISA. Our results demonstrate that the quantum environment is not a passive spectator during inflation, but an active agent whose imprint on the primordial universe may be within reach of the next generation of cosmological observations.

astro-ph.CO↗

arXiv2025

Quantum Recoherence in Presence of Excited States in the Early Universe

We investigate the quantum-to-classical transition of primordial perturbations within a two-field inflationary framework where an adiabatic mode interacts with an entropic environment. In the case of a massive entropic environment, the attractor Bunch--Davies vacuum plays a special role: it is the only state that can undergo full recoherence, whereas all excited initial states exhibit persistent loss of purity. To characterize this behavior, we parameterize excited Gaussian initial states by their Bogoliubov coefficients and compute the purity and Rényi-2 entropy of the reduced adiabatic state as information-theoretic indicators of decoherence dynamics. We find that excited states display \emph{purity-freezing} at a non-zero plateau, where residual quantum correlations persist indefinitely, a qualitative departure from the complete recoherence observed for the Bunch--Davies vacuum. This sensitivity to initial conditions highlights the non-generic nature of full recoherence in the quantum-to-classical transition of inflationary perturbations.

gr-qc↗

arXiv2025

Current constraints on cosmological scenarios with very low reheating temperatures

We present a comprehensive analysis of the effects of models with very low reheating scenarios ($T_\text{RH} \sim \mathcal{O}(\text{MeV})$) on the cosmological observables and derive corresponding bounds on the reheating temperature. With respect to previous work, our study includes a more precise computation of neutrino distribution functions, leveraging the latest datasets from cosmological surveys. We perform a joint analysis that combines constraints from Big Bang Nucleosynthesis, the Cosmic Microwave Background, and galaxy surveys, alongside separate investigations of these datasets, carefully assessing the impact of different choices of priors. At the $95\%$ confidence level, we establish a lower bound on the reheating temperature of $T_\text{RH} > 5.96 \; \text{MeV} $, representing the most stringent constraint to date.

astro-ph.CO↗

arXiv2024

Steepest Growth in the Primordial Power Spectrum from Excited States at a Sudden Transition

Sudden phase transitions during inflation can give rise to strongly enhanced primordial density perturbations on scales much smaller than those directly probed by cosmic microwave background anisotropies. In this paper, we study the effect of the incoming quantum state on the steepest growth found in the primordial power spectrum using a simple model of an instantaneous transition during single-field inflation. We consider the case of a general de Sitter-invariant initial state for the inflaton field (the $α$-vacuum), and also an incoming state perturbed by a preceding transition. For the $α$-vacua we find that $k^6$ growth is possible for $α>0$, while $k^4$ growth is seen for $α\leq0$, including the standard case of an initial Bunch-Davies vacuum state. The features of an enhanced primordial power spectrum on small scales are thus sensitive to the initial quantum state during inflation. We calculate the scalar-induced gravitational wave power spectrum for each case.

astro-ph.CO↗

arXiv2023

Neff in the Standard Model at NLO is 3.043

The effective number of relativistic neutrino species is a fundamental probe of the early Universe and its measurement represents a key constraint on many scenarios beyond the Standard Model of Particle Physics. In light of this, an accurate prediction of $N_{\rm eff}$ in the Standard Model is of pivotal importance. In this work, we consider the last ingredient needed to accurately calculate $N_{\rm eff}^{\rm SM}$: standard zero and finite temperature QED corrections to $e^+e^- \leftrightarrow ν\barν$ interaction rates during neutrino decoupling at temperatures around $T\sim {\rm MeV}$. We find that this effect leads to a reduction of $-0.0007$ in $N_{\rm eff}^{\rm SM}$. This NLO QED correction to the interaction rates, together with finite temperature QED corrections to the electromagnetic density of the plasma, and the effect of neutrino oscillations, implies that $N_{\rm eff}^{\rm SM} = 3.043$ with a theoretical uncertainty that is much smaller than any projected observational sensitivity.

hep-ph↗

arXiv2023

Gravitational Wave non-Gaussianity from trans-Planckian Quantum Noise

We examine the effect of a trans-Planckian phase on the dynamics of inflationary tensor perturbations. To remedy the fact that this regime is not fully captured by standard perturbation theory, we introduce an effective quantum noise source, whose role is regulated by the energy scale $Λ$. The presence of the source modifies the initial conditions for the tensor modes, leaving a distinct imprint. We study the amplitude and shape of the gravitational wave bispectrum of the model and compare these with their counterparts obtained under the assumptions of Bunch-Davies initial conditions and $α$-vacua states. Depending on the value of the scale $Λ$, we find distinctive signatures associated with both the bispectrum shape and the non-linear parameter $f_{\rm NL}$.

gr-qc↗

arXiv2022

Impact of trans-Planckian quantum noise on the Primordial Gravitational Wave spectrum

We investigate the impact of stochastic quantum noise due to trans--Planckian effects on the primordial power spectrum for gravity waves during inflation. Given an energy scale Lambda, expected to be close to the Planck scale m_Pl and larger than the Hubble scale H, this noise is described in terms of a source term in the evolution equation for comoving modes k which changes its amplitude growth from early times as long as the mode physical wavelength is smaller than Lambda^-1. We model the source term as due to a gas of black holes in the trans--Planckian regime and the corresponding Hawking radiation. In fact, for energy scales larger than, or of the order of Lambda, it is expected that trapped surfaces may form due to large energy densities. At later times the evolution then follows the standard sourceless evolution. We find that this mechanism still leads to a scale-invariant power spectrum of tensor perturbations, with an amplitude that depends upon the ratio Lambda/m_Pl.

gr-qc↗

arXiv2021

KM3NeT/ARCA expectations in view of a novel multimessenger study of starburst galaxies

Starburst galaxies (SBGs) and more in general starforming galaxies represent a class of galaxies with a high star formation rate (up to 100 solar masses/year). Despite their low luminosity, they can 19 be considered as guaranteed "factories" of high energy neutrinos, being "reservoirs" of accelerated 20 cosmic rays and hosting a high density target gas in the central region. In this contribution 21 we present a novel multimessenger study of these sources and the possibility of observing their 22 neutrino signals with the KM3NeT/ARCA telescope. The differential sensitivity for different SBG 23 scenarios is reported considering track-like neutrino events in the 100 GeV-100 PeV energy range.

astro-ph.HE↗

arXiv2021

Sensitivity of KM3NeT to Violation of Equivalence Principle

The symmetry of the theory of relativity under diffeomorphisms strongly depends on the equivalence principle. Violation of Equivalence Principle (VEP) can be tested by looking for deviations from the standard framework of neutrino oscillations. In recent works, it has been shown that strong constraints on the VEP parameter space can be placed by means of the atmospheric neutrinos observed by the IceCube neutrino telescope. In this paper, we focus on the KM3NeT neutrino telescope and perform a forecast analysis to assess its capacity to probe VEP. Most importantly, we examine the crucial role played by systematic uncertainties affecting the neutrino observations. We find that KM3NeT will constrain VEP parameters times the local gravitational potential at the level of $10^{-27}$. Due to the systematic-dominated regime, independent analyses from different neutrino telescopes are fundamental for robustly testing the equivalence principle.

hep-ph↗

arXiv2021

IceCube constraints on Violation of Equivalence Principle

Among the information provided by high energy neutrinos, a promising possibility is to analyze the effects of a Violation of Equivalence Principle (VEP) on neutrino oscillations. We analyze the recently released IceCube data on atmospheric neutrino fluxes under the assumption of a VEP and obtain updated constraints on the parameter space with the benchmark choice that neutrinos with different masses couple with different strengths to the gravitational field. In this case we find that the VEP parameters times the local gravitational potential at Earth can be constrained at the level of $10^{-27}$. We show that the constraints from atmospheric neutrinos strongly depend on the assumption that the neutrino eigenstates interacting diagonally with the gravitational field coincide with the mass eigenstates, which is not \textit{a priori} justified: this is particularly clear in the case that the basis of diagonal gravitational interaction coincide with the flavor basis, which cannot be constrained by the observation of atmospheric neutrinos. Finally, we quantitatively study the effect of a VEP on the flavor composition of the astrophysical neutrinos, stressing again the interplay with the basis in which the VEP is diagonal: we find that for some choices of such basis the flavor ratio measured by IceCube can significantly change.

hep-ph↗

arXiv2021

Starburst galaxies strike back: a multi-messenger analysis with Fermi-LAT and IceCube data

Starburst galaxies, which are known as "reservoirs" of high-energy cosmic-rays, can represent an important high-energy neutrino "factory" contributing to the diffuse neutrino flux observed by IceCube. In this paper, we revisit the constraints affecting the neutrino and gamma-ray hadronuclear emissions from this class of astrophysical objects. In particular, we go beyond the standard prototype-based approach leading to a simple power-law neutrino flux, and investigate a more realistic model based on a data-driven blending of spectral indexes, thereby capturing the observed changes in the properties of individual emitters. We then perform a multi-messenger analysis considering the extragalactic gamma-ray background (EGB) measured by Fermi-LAT and different IceCube data samples: the 7.5-year High-Energy Starting Events (HESE) and the 6-year high-energy cascade data. Along with starburst galaxies, we take into account the contributions from blazars and radio galaxies as well as the secondary gamma-rays from electromagnetic cascades. Remarkably, we find that, differently from the highly-constrained prototype scenario, the spectral index blending allows starburst galaxies to account for up to $40\%$ of the HESE events at $95.4\%$ CL, while satisfying the limit on the non-blazar EGB component. Moreover, values of $\mathcal{O}(100~\mathrm{PeV})$ for the maximal energy of accelerated cosmic-rays by supernovae remnants inside the starburst are disfavoured in our scenario. In broad terms, our analysis points out that a better modeling of astrophysical sources could alleviate the tension between neutrino and gamma-ray data interpretation.

astro-ph.HE↗

arXiv2020

Primordial Deuterium after LUNA: concordances and error budget

The accurate evaluation of the nuclear reaction rates and corresponding uncertainties is an essential requisite for a precise determination of light nuclide primordial abundances. The recent measurement of the D(p,gamma)3He radiative capture cross section by the LUNA collaboration, with its order 3% error, represents an important step in improving the theoretical prediction for Deuterium produced in the early universe. In view of this recent result, we present in this paper a full analysis of its abundance, which includes a new critical study of the impact of the other two main processes for Deuterium burning, namely the deuteron-deuteron transfer reactions, D(d,p)3H and D(d,n)3He. In particular, emphasis is given to the statistical method of analysis of experimental data, to a quantitative study of the theoretical uncertainties, and a comparison with similar studies presented in the recent literature. We then discuss the impact of our study on the concordance of the primordial nucleosynthesis stage with the Planck experiment results on the baryon density Omegab h2 and the effective number of neutrino parameter Neff, as function of the assumed value of the 4He mass fraction Yp. While after the LUNA results, the value of Deuterium is quite precisely fixed, and points to a value of the baryon density in excellent agreement with the Planck result, a combined analysis also including Helium leads to two possible scenarios with different predictions for Omegab h2 and Neff. We argue that new experimental results on the systematics and the determination of Yp would be of great importance in assessing the overall concordance of the standard cosmological model.

astro-ph.CO↗

arXiv2020

Tau Neutrinos with Cherenkov Telescope Array

The next generation of Imaging Atmospheric Cherenkov telescope, like CTA, is going to strongly improve the detection capability of high-energy cosmic rays. In our paper we discuss the possibility to use such apparatus to detect Earth-skimming tau neutrinos. Interestingly the analysis shows that order few events per year can be detected for energies above $10^8$ GeV in the optimistic case of larger neutrino fluxes produced by Flat Spectrum Radio Quasars. However, even for more conservative cosmogenic neutrino fluxes such rate will be also obtained, but for a decade of running. This estimate seems to candidate a set up like CTA for performing high energy neutrino astronomy as well.

hep-ph↗

arXiv2020

Decaying dark matter at IceCube and its signature on High Energy gamma experiments

The origin of neutrino flux observed in IceCube is still mainly unknown. Typically two flux components are assumed, namely: atmospheric neutrinos and an unknown astrophysical term. In principle the latter could also contain a top-down contribution coming for example from decaying dark matter. In this case one should also expect prompt and secondary gammas as well. This leads to the possibility of a multimessenger analysis based on the simultaneous comparison of the Dark Matter hypothesis both with neutrino and high energy gamma rays data. In this paper, we analyze, for different decaying Dark Matter channels, the 7.5 years IceCube HESE data, and compare the results with previous exclusion limits coming from Fermi data. Finally, we test whether the Dark Matter hypothesis could be further scrutinised by using forthcoming high energy gamma rays experiments.

hep-ph↗

arXiv2019

Astrophysical neutrinos: theory

In the era of multi-messenger astronomy, neutrinos are among the most important astronomical messengers, due to their interaction properties. In these lessons I briefly review the main issues concerning the theory on astrophysical neutrinos.

astro-ph.CO↗

arXiv2018

Neutrino phenomenology from leptogenesis

Assuming a type-I seesaw mechanism for neutrino mass generation and invoking a baryogengesis via leptogenesis scenario, we consider a reasonable hierarchical structure for Dirac neutrino mass matrix, similar to up-type quark mass matrix. These hypotheses imply a relevant connection between high scale CP violation and low energy one. By requiring a compact heavy neutrino mass spectrum, which allows to circumvent Davidson-Ibarra limit, one can obtain an efficient leptogenesis restricting the allowed region for low energy neutrino parameters. Once the oscillating parameters are taken inside a $3σ$ range, through the numerical resolution of the leptogenesis Boltzmann equations one gets the following allowed intervals for the lightest neutrino mass and the Dirac CP phase: $-0.90π<δ<-0.75π$ and $m_1\sim( 0.002 - 0.004)$ eV.

hep-ph↗

arXiv2017

Cosmic Neutrinos

Neutrinos are key astronomical messengers, because they are undeflected by magnetic field and unattenuated by electromagnetic interaction. After the first detection of extraterrestrial neutrinos in the TeV-PeV region by Neutrino Telescopes we are entering a new epoch where neutrino astronomy becomes possible. In this paper I briefly review the main issues concerning cosmological neutrinos and their experimental observation.

astro-ph.CO↗