arXiv subjects

Jordi Salvado

Publications and source records attributed to Jordi Salvado.

At least 19 recordsLinked to original sources

arXiv2026

BBN bounds on neutrinophilic ultralight Dark Matter

The high densities in the early Universe provide a unique laboratory to constrain couplings between feebly interacting particles, such as dark matter and neutrinos. In this article, we study how Big Bang Nucleosynthesis can constrain models of Ultra-Light Dark Matter diagonally coupled to neutrinos. We follow an adiabatic formalism which allows to average-out the rapid oscillations of the Dark Matter field and consistently take into account the feedback between the neutrino and the Dark Matter fields. This feedback alters the early Universe dynamics, causing the Dark Matter energy density to scale as radiation, while the neutrino mass scales as $a^{-1}$. These two effects modify primordial element abundances by modifying interaction rates and the expansion rate during nucleosynthesis. Then, we use primordial abundances to obtain leading cosmological bounds on the coupling in the range $m_ϕ/{\rm eV}\in (10^{-22},10^{-17})$, namely $g\lesssim 0.13(m_ϕ/{\rm eV})$ for $m_ϕ\gtrsim 3\times 10^{-20}\,\rm eV$ and $g\lesssim 1.8\times 10^{-11}\sqrt{m_ϕ/\rm eV}$ for $m_ϕ\lesssim 3\times 10^{-20}\,\rm eV$. This consistent cosmological treatment emphasizes that, in the mass interval where its physical assumptions hold, neutrino masses cannot be generated refractively by a direct coupling with an Ultra-Light Dark Matter field.

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arXiv2026

Seafloor Topography Enhances KM3NeT Sensitivity to ANITA-like Events

In this article, we introduce the concept of topographic enhancement in the context of ultra-high-energy neutrino detection by underwater neutrino telescopes. We demonstrate that the local topography around KM3NeT/ARCA can increase the detection efficiency in scenarios involving long-lived particles by up to a factor of $\sim 3$ due to the presence of an underwater mountain range in the direction of Malta. We consider a simplified model-independent approach that parametrizes the new physics able to generate both track-like and cascade-like signals in neutrino telescopes. When explaining the KM3-230213A event with a diffuse dark flux hypothesis, including its azimuthal direction--in addition to the zenith angle--provides additional constraints on the parameter space. In this effective model, the observations by KM3NeT and ANITA-IV can be simultaneously explained, but a global tension with the lack of a corresponding detection in IceCube remains at 2.7 sigma. This work underscores the importance of incorporating topographic effects in the design and optimization of next-generation neutrino telescopes, as is done in the context of mountain-based detectors such as TAMBO. We present a numerical code which can be used to easily extend this topographical analysis to other experiments.

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arXiv2026

Earth rotation turns event timing into a geometric probe of UHE neutrino origin

It has been proposed that the ultra-high-energy (UHE) event $\rm KM3-230213A$ detected by KM3NeT could be explained by dark matter (DM) decay. Prima facie this seems unlikely because the arrival direction of the event is opposite to the Galactic Centre. We develop a per-event test statistic to quantitively assess this possibility and forecast the required future events to exclude the DM hypothesis in favour of an isotropic signal. For the single event observed, the DM decay hypothesis is disfavoured but not excluded ($p\text{-value}_{\rm DM}\simeq0.13$--$0.15$). We emphasise how including the time-averaged detector visibility helps discrimination despite reducing the proportion of visible sky, reducing the number of events for exclusion from $\sim33$--$43$ to $\sim22$--$27$. Moving beyond this, we perform a fully time-resolved forecast and find that the required number of events for exclusion reduces by $40\%$, $\sim14$--$16$. The time variation in the signal provides vital information allowing one to exclude or confirm the DM hypothesis with much fewer events. Our results are robust against DM decay channels and halo distributions and can readily be applied to other relics distributed similarly. Our framework allows one to turn event timing into a probe of signal geometry and is generic to any UHE equatorial neutrino telescopes.

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arXiv2025

Origin of cosmological neutrino mass bounds: background $\textit{versus}$ perturbations

The cosmological upper bound on the total neutrino mass is the dominant limit on this fundamental parameter. Recent observations-soon to be improved-have strongly tightened it, approaching the lower limit set by oscillation data. Understanding its physical origin, robustness, and model-independence becomes pressing. Here, we explicitly separate for the first time the two distinct cosmological neutrino-mass effects: the impact on background evolution, related to the energy in neutrino masses; and the "kinematic" impact on perturbations, related to neutrino free-streaming. We scrutinize how they affect CMB anisotropies, introducing two effective masses enclosing $\textit{background}$ ($\sum m_ν^\mathrm{Backg.}$) and $\textit{perturbations}$ ($\sum m_ν^\mathrm{Pert.}$) effects. We analyze CMB data, finding that the neutrino-mass bound is mostly a background measurement, i.e., how the neutrino energy density evolves with time. The bound on the "kinematic" variable $\sum m_ν^\mathrm{Pert.}$ is largely relaxed, $\sum m_ν^\mathrm{Pert.} < 0.8\,\mathrm{eV}$. This work thus adds clarity to the physical origin of the cosmological neutrino-mass bound, which is mostly a measurement of the neutrino equation of state, providing also hints to evade such a bound.

astro-ph.CO↗

arXiv2023

On neutrino-mediated potentials in a neutrino background

The exchange of a pair of neutrinos with Standard Model weak interactions generates a long-range force between fermions. The associated potential is extremely feeble, $\propto G_F^2/r^5$ for massless neutrinos, whichrenders it far from observable even in the most sensitive experiments testing fifth forces. The presence of a neutrino background has been argued to induce a correction to the neutrino propagator that enhances the potential by orders of magnitude. In this brief note, we point out that such modified propagators are invalid if the background neutrino wavepackets have a finite width. By reevaluating the 2--$ν$ exchange potential in the presence of a neutrino background including finite width effects, we find that the background-induced enhancement is reduced by several orders of magnitude. Unfortunately, this pushes the resulting 2--$ν$ exchange potential away from present and near-future sensitivity of tests of new long-range forces.

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arXiv2023

IceCube and the origin of ANITA-IV events

Recently, the ANITA collaboration announced the detection of new, unsettling upgoing Ultra-High-Energy (UHE) events. Understanding their origin is pressing to ensure success of the incoming UHE neutrino program. In this work, we study their internal consistency and the implications of the lack of similar events in IceCube. We introduce a generic, simple parametrization to study the compatibility between these two observatories in Standard Model-like and Beyond Standard Model scenarios: an incoming flux of particles that interact with Earth nucleons with cross section $σ$, producing particle showers along with long-lived particles that decay with lifetime $τ$ and generate a shower that explains ANITA observations. We find that the ANITA angular distribution imposes significant constraints, and when including null observations from IceCube only $τ\sim 10^{-3}$ - $10^{-2} \,\mathrm{s}$ and $σ\sim 10^{-33}$ - $10^{-32}\,\mathrm{cm^2}$ can explain the data. This hypothesis is testable with future IceCube data. Finally, we discuss a specific model that can realize this scenario. Our analysis highlights the importance of simultaneous observations by high-energy optical neutrino telescopes and new UHE radio detectors to uncover cosmogenic neutrinos or discover new physics.

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arXiv2023

Impact of Wave Packet Separation in Low-Energy Sterile Neutrino Searches

Light sterile neutrinos have been motivated by anomalies observed in short-baseline neutrino experiments.Among them, radioactive-source and reactor experiments have provided evidence and constraints, respectively, for electron neutrino disappearance compatible with an eV-scale neutrino. The results from these observations are seemingly in conflict. This letter brings into focus the assumption that the neutrino wave packet can be approximated as a plane wave, which is adopted in all analyses of such experiments. We demonstrate that the damping of oscillations, e.g., due to a finite wave packet size, solve the tension between these electron-flavor observations and constraints.

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arXiv2022

Non-standard neutrino cosmology dilutes the lensing anomaly

Despite the impressive success of the standard cosmological model, several anomalies defy its triumph. Among them is the so-called lensing anomaly: the Planck satellite observes stronger CMB gravitational lensing than expected. The role of neutrinos in this anomaly has been mostly overlooked, despite their key role in CMB lensing, because in the standard scenario they tend to increase the tension. Here, we show that this strongly depends on the assumed neutrino equation of state. We demonstrate that if neutrinos have yet undiscovered long-range interactions, the lensing pattern is significantly affected, rendering the lensing anomaly as a statistical fluctuation. Our results thus open up a window to link anomalous CMB lensing with present and future cosmological, astrophysical, and laboratory measurements of neutrino properties.

astro-ph.CO↗

arXiv2021

nuSQuIDS: A toolbox for neutrino propagation

The Neutrino Simple Quantum Integro-Differential Solver (nuSQuIDS) is a C++ code based on SQuIDS that propagates an ensemble of neutrinos through given media. Neutrino oscillation calculations relevant to current and next-generation experiments are implemented. This includes coherent and non-coherent neutrino interactions in settings such as the Sun, Earth, or a vacuum. The code is designed to be accurate and flexible, while at the same time maintaining good performance. It has a modular design that allows the user to incorporate new physics in novel scenarios.

hep-ph↗

arXiv2021

Sterile neutrinos with neutrino telescopes

Searches for light sterile neutrinos are motivated by the unexpected observation of electron neutrino appearance in short-baseline experiments, such as the Liquid Scintillator Neutrino Detector (LSND) and the Mini Booster Neutrino Experiment (MiniBooNE). In light of these unexpected results, a campaign using natural and anthropogenic sources to find light -- mass-squared-difference around 1 eV$^{2}$ -- sterile neutrinos is underway. Among the natural sources, atmospheric neutrinos provide a unique gateway to search for sterile neutrinos due to the broad range of baseline-to-energy ratios, $L/E$, and the presence of significant matter effects. Since the atmospheric neutrino flux rapidly falls with energy, studying its highest energy component requires gigaton-scale neutrino detectors. These detectors -- often known as neutrino telescopes since they are designed to observe tiny astrophysical neutrino fluxes -- have performed searches for light sterile neutrinos and have found no significant signal to date. This brief review summarizes the current status of searches for light sterile neutrinos with neutrino telescopes deployed in solid and liquid water.

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arXiv2021

Long Range Interactions in Cosmology: Implications for Neutrinos

Cosmology is well suited to study the effects of long range interactions due to the large densities in the early Universe. In this article, we explore how the energy density and equation of state of a fermion system diverge from the commonly assumed ideal gas form under the presence of scalar long range interactions with a range much smaller than cosmological scales. In this scenario, "small"-scale physics can impact our largest-scale observations. As a benchmark, we apply the formalism to self-interacting neutrinos, performing an analysis to present and future cosmological data. Our results show that the current cosmological neutrino mass bound is fully avoided in the presence of a long range interaction, opening the possibility for a laboratory neutrino mass detection in the near future. We also demonstrate an interesting complementarity between neutrino laboratory experiments and the future EUCLID survey.

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arXiv2020

Updated Constraints on Non-Standard Interactions from Global Analysis of Oscillation Data

We quantify our present knowledge of the size and flavor structure of non-standard neutrino interactions which affect the matter background in the evolution of solar, atmospheric, reactor and long-baseline accelerator neutrinos as determined by a global analysis of oscillation data - both alone and in combination with the results on coherent neutrino-nucleus scattering from the COHERENT experiment. We consider general neutral current neutrino interactions with quarks whose lepton-flavor structure is independent of the quark type. We study the dependence of the allowed ranges of non-standard interaction coefficients, the status of the LMA-D solution, and the determination of the oscillation parameters on the relative strength of the non-standard couplings to up and down quarks. Generically we find that the conclusions are robust for a broad spectrum of up-to-down strengths, and we identify and quantify the exceptional cases related to couplings whose effect in neutrino propagation in the Earth or in the Sun is severely suppressed. As a result of the study we provide explicit constraints on the effective couplings which parametrize the non-standard Earth matter potential relevant for long-baseline experiments.

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arXiv2020

Axion Gegenschein: Probing Back-scattering of Astrophysical Radio Sources Induced by Dark Matter

We investigate a novel technique for the astrophysical detection of axions or axion-like particles in the dark matter halo of the Milky Way based on stimulated decay of axions, which we call axion gegenschein emission. Photons from the brightest known radio sources with a frequency equal to half the axion mass stimulate axion decay while propagating through the dark matter halo, causing radio emission in a direction precisely opposite to the incoming photon in the axion rest-frame and creating a countersource for every radio source, with an image smoothed by the dark matter velocity dispersion. We calculate the flux of the axion gegenschein countersource of Cygnus A, the brightest extragalactic radio source, and the limits that can be set with SKA to the axion-photon coupling constant $g_{aγ}$. We find this method to be more powerful than previous proposals based on searching for radio emission from axion decay in nearby dwarf galaxies or the Milky Way. The forecasted limits remain considerably higher than predictions from QCD axion models, and limits that can be set with laboratory searches of radio waves generated in resonant cavities with strong magnetic fields similar to the ADMX experiment, although this observation would directly measure a column density of dark matter through the Galactic halo and is therefore not affected by possible substructure in the dark matter distribution.

astro-ph.CO↗

arXiv2020

Looking at the axionic dark sector with ANITA

The ANITA experiment has recently observed two anomalous events emerging from well below the horizon. Even though they are consistent with tau cascades, a high energy Standard Model or Beyond the Standard Model explanation is challenging and in tension with other experiments. We study under which conditions the reflection of generic radio pulses can reproduce these signals. We propose that these pulses can be resonantly produced in the ionosphere via axion-photon conversion. This naturally explains the direction and polarization of the events and avoids other experimental bounds.

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arXiv2020

Probe Of Sterile Neutrinos Using Astrophysical Neutrino Flavor

In this paper, we study the effect of active-neutrino-sterile-neutrino mixing in the expected high-energy astrophysical neutrino flavor content. Non-unitarity in the measurement of the three active neutrinos can be due to the existence of sterile neutrino states. We introduce the concept of the four-flavor tetrahedron in order to visualize the lack of unitarity in the astrophysical neutrino three-flavor triangle. We demonstrate that active-sterile neutrino mixings modify the allowed region of the astrophysical flavor ratio from the standard case. However, a projection of the four-flavor tetrahedron has restrictions of phase space similar to the three-flavor triangle. On the other hand, the initial presence of astrophysical sterile neutrinos drastically changes the scenario, and it allows an apparent unitarity violation in the three-flavor triangle space. Using current global fit constraints including the non-unitarity case, we also illustrate the allowed astrophysical neutrino flavor ratios. Thus, the measurement of the high-energy astrophyscal neutrino flavor content allows us to explore sterile neutrinos independently of the sterile neutrino mass scale. These are topics of investigation for current and future neutrino telescopes.

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arXiv2019

Neutrino Non-Standard Interactions: A Status Report

This report summarizes the present status of neutrino non-standard interactions (NSI). After a brief overview, several aspects of NSIs are discussed, including connection to neutrino mass models, model-building and phenomenology of large NSI with both light and heavy mediators, NSI phenomenology in both short- and long-baseline neutrino oscillation experiments, neutrino cross-sections, complementarity of NSI with other low- and high-energy experiments, fits with neutrino oscillation and scattering data, DUNE sensitivity to NSI, effective field theory of NSI, as well as the relevance of NSI to dark matter and cosmology. We also discuss the open questions and interesting future directions that can be pursued by the community at large. This report is based on talks and discussions during the Neutrino Theory Network NSI workshop held at Washington University in St. Louis from May 29-31, 2019 (https://indico.cern.ch/event/812851/)

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arXiv2019

Fundamental physics with high-energy cosmic neutrinos today and in the future

The astrophysical neutrinos discovered by IceCube have the highest detected neutrino energies --- from TeV to PeV --- and likely travel the longest distances --- up to a few Gpc, the size of the observable Universe. These features make them naturally attractive probes of fundamental particle-physics properties, possibly tiny in size, at energy scales unreachable by any other means. The decades before the IceCube discovery saw many proposals of particle-physics studies in this direction. Today, those proposals have become a reality, in spite of astrophysical unknowns. We will showcase examples of doing fundamental neutrino physics at these scales, including some of the most stringent tests of physics beyond the Standard Model. In the future, larger neutrino energies --- up to tens of EeV --- could be observed with larger detectors and further our reach.

astro-ph.HE↗

arXiv2019

How to relax the cosmological neutrino mass bound

We study the impact of non-standard momentum distributions of cosmic neutrinos on the anisotropy spectrum of the cosmic microwave background and the matter power spectrum of the large scale structure. We show that the neutrino distribution has almost no unique observable imprint, as it is almost entirely degenerate with the effective number of neutrino flavours, $N_{\mathrm{eff}}$, and the neutrino mass, $m_ν$. Performing a Markov chain Monte Carlo analysis with current cosmological data, we demonstrate that the neutrino mass bound heavily depends on the assumed momentum distribution of relic neutrinos. The message of this work is simple and has to our knowledge not been pointed out clearly before: Cosmology allows that neutrinos have larger masses if their average momentum is larger than that of a perfectly thermal distribution. Here we provide an example in which the mass limits are relaxed by a factor of two.

astro-ph.CO↗