arXiv subjects

S. Rosauro-Alcaraz

Publications and source records attributed to S. Rosauro-Alcaraz.

At least 19 recordsLinked to original sources

arXiv2026

Interpreting the results on exclusive $c\rightarrow sμν$ modes

We examine the $q^2$-binned distributions of the $D\to Kμν$ decay rate and of the corresponding forward-backward asymmetry which were recently measured by BESIII, showing a mild deviation from the Standard Model predictions. We point out that the proposed solution to remedy the discrepancy by turning on a complex-valued New Physics coupling is in tension with the constraints deduced from the LHC bounds on the high-$p_T$ tail of the relevant Drell-Yan process. We then show that there are several plausible scenarios that are compatible with both the measured low-energy and high-energy constraints but the selected couplings appear to be too small to be observed in the measurements of integrated observables, except for possibly the $q^2$-binned distribution of the angular observables relevant to $D_s\to ϕ(\to KK) μν$ or $Λ_c\to Λ(\to p π) μν$ modes.

hep-ph↗

arXiv2026

Cosmological phase transitions: from particle physics to gravitational waves, semi-analytically

Motivated by the recent evidence of a stochastic gravitational wave background found by pulsar timing array experiments, we focus on one of the prime cosmological explanations, i.e. a supercooled first order phase transition. If confirmed, it would offer a unique opportunity to probe early Universe dynamics and the related physics beyond the Standard Model of particles and interactions. However, the prediction of the gravitational wave spectrum from a given particle physics scenario requires theoretically and computationally demanding methods. While several tools have been put forward to reduce uncertainties and automatize these computations, we study here the possibility to perform the full pipeline of computations semi-analytically in the $4D$ theory for a $U(1)^\prime$ conformal extension of the Standard Model, thus avoiding computationally intensive simulations. Our approach yields accurate results that can be used in phenomenological studies and allow for an efficient exploration of the connection between the particle physics models and their cosmological predictions.

hep-ph↗

arXiv2025

Testable dark matter solution within the seesaw mechanism

The presence of a dark matter component in the Universe, together with the discovery of neutrino masses from the observation of the oscillation phenomenon, represents one of the most important open questions in particle physics today. A concurrent solution arises when one of the right-handed neutrinos, necessary for the generation of light neutrino masses, is itself the dark matter candidate. In this article, we study the generation of such a dark matter candidate relying solely on the presence of neutrino mixing. This tightly links the generation of dark matter with searches in laboratory experiments on top of the usual indirect dark matter probes. We find that the regions of parameter space producing the observed dark matter abundance can be probed indirectly with electroweak precision observables and charged lepton flavor violation searches. Given that the heavy neutrino masses need to lie at most around the TeV scale, probes at future colliders would further test this production mechanism.

hep-ph↗

arXiv2024

White Paper on Light Sterile Neutrino Searches and Related Phenomenology

This white paper provides a comprehensive review of our present understanding of experimental neutrino anomalies that remain unresolved, charting the progress achieved over the last decade at the experimental and phenomenological level, and sets the stage for future programmatic prospects in addressing those anomalies. It is purposed to serve as a guiding and motivational "encyclopedic" reference, with emphasis on needs and options for future exploration that may lead to the ultimate resolution of the anomalies. We see the main experimental, analysis, and theory-driven thrusts that will be essential to achieving this goal being: 1) Cover all anomaly sectors -- given the unresolved nature of all four canonical anomalies, it is imperative to support all pillars of a diverse experimental portfolio, source, reactor, decay-at-rest, decay-in-flight, and other methods/sources, to provide complementary probes of and increased precision for new physics explanations; 2) Pursue diverse signatures -- it is imperative that experiments make design and analysis choices that maximize sensitivity to as broad an array of these potential new physics signatures as possible; 3) Deepen theoretical engagement -- priority in the theory community should be placed on development of standard and beyond standard models relevant to all four short-baseline anomalies and the development of tools for efficient tests of these models with existing and future experimental datasets; 4) Openly share data -- Fluid communication between the experimental and theory communities will be required, which implies that both experimental data releases and theoretical calculations should be publicly available; and 5) Apply robust analysis techniques -- Appropriate statistical treatment is crucial to assess the compatibility of data sets within the context of any given model.

hep-ex↗

arXiv2024

Disentangling left and right-handed neutrino effects in $B\rightarrow K^{(*)}νν$

The first observation of $\mathcal{B}\left(B^+\rightarrow K^+νν\right)$ by the Belle II experiment lies almost $3σ$ away from the Standard Model expectation. In this letter we study this result in the SMEFT, extended by a light right-handed neutrino. We explore the correlations between the measured decay rate and other observables, such as $\mathcal{B}\left(B\rightarrow K^*νν\right)$ and $F_L\left(B\rightarrow K^*νν\right)$, showing that they could disentangle among scenarios involving left-handed neutrinos and those with the right-handed ones. Furthermore, we find that the high-$p_T$ tails of Drell-Yan processes studied at LHC provide important constraints that help us exclude some of the scenarios consistent with the Belle II result.

hep-ph↗

arXiv2023

$ν$ Electroweak Baryogenesis: The Scalar Singlet Strikes Back

We perform a thorough scan of the parameter space of a general singlet scalar extension of the Standard Model to identify the regions which can lead to a strong first-order phase transition, as required by the electroweak baryogenesis mechanism. We find that taking into account bubble nucleation is a fundamental constraint on the parameter space and present a conservative and fast estimate for it to enable efficient parameter space scanning. The allowed regions turn out to be already significantly probed by constraints on the scalar mixing from Higgs signal strength measurements. We also consider the addition of new neutrino singlet fields with Yukawa couplings to both scalars and forming heavy (pseudo)-Dirac pairs, as in the linear or inverse see-saw mechanisms for neutrino mass generation. Interestingly, we identify an interplay between the strength of the phase transition and the stability of the electroweak vacuum which prevents these Yukawa couplings to become arbitrarily large. Thus, their inclusion does not alter the early universe phenomenology or allowed parameter space in a significant way. Conversely, we find allowed regions of the parameter space where the presence of the neutrino singlets would remarkably modify the collider phenomenology, yielding interesting new signatures in Higgs and singlet scalar decays.

hep-ph↗

arXiv2023

Thermal effects in freeze-in neutrino dark matter production

We present a detailed study of the production of dark matter in the form of a sterile neutrino via freeze-in from decays of heavy right-handed neutrinos. Our treatment accounts for thermal effects in the effective couplings, generated via neutrino mixing, of the new heavy neutrinos with the Standard Model gauge and Higgs bosons and can be applied to several low-energy fermion seesaw scenarios featuring heavy neutrinos in thermal equilibrium with the primordial plasma. We find that the production of dark matter is not as suppressed as to what is found when considering only Standard Model gauge interactions. Our study shows that the freeze-in dark matter production could be efficient.

hep-ph↗

arXiv2023

Impact of CPV phases on flavour violating $H$ and $Z$ decays

Standard Model extensions via heavy neutral leptons lead to modifications in the lepton mixing matrix, including new Dirac and Majorana CP violating phases. Here we consider the role of the Majorana fermions and of new CP violating phases in Higgs and $Z$-boson lepton flavour violating decays, as well as in the corresponding CP-asymmetries. We confirm that these decays are sensitive to the presence of additional sterile states and show that the new CP violating phases may lead to both destructive and constructive interferences in the decay rates. Interestingly the $Z\to μ^\pmτ^\mp$ rates are within FCC-ee reach, with associated CP-asymmetries that can potentially reach up to 30%.

hep-ph↗

arXiv2023

The ESSnuSB design study: overview and future prospects

ESSnuSB is a design study for an experiment to measure the CP violation in the leptonic sector at the second neutrino oscillation maximum using a neutrino beam driven by the uniquely powerful ESS linear accelerator. The reduced impact of systematic errors on sensitivity at the second maximum allows for a very precise measurement of the CP violating parameter. This review describes the fundamental advantages of measurement at the 2nd maximum, the necessary upgrades to the ESS linac in order to produce a neutrino beam, the near and far detector complexes, the expected physics reach of the proposed ESSnuSB experiment, concluding with the near future developments aimed at the project realization.

hep-ex↗

arXiv2023

Heavy neutral lepton corrections to SM boson decays: lepton flavour universality violation in low-scale seesaw realisations

We study lepton flavour universality violation in SM boson decays in low-scale seesaw models of neutrino mass generation, also addressing other electroweak precision observables. We compute the electroweak next-to-leading order corrections, which turn out to be important - notably in the case of the invisible decay width of the $Z$ boson, for which the corrections can be as large as the current experimental uncertainty. As a well-motivated illustrative study case, we choose a realisation of the Inverse Seesaw mechanism, and discuss the complementary role of lepton flavour conserving, lepton flavour violating and precision observables, both in constraining and in probing such models of neutrino mass generation. Our findings suggest that invisible $Z$ decays are especially important, potentially at the origin of the most stringent constraints for certain regimes of the Inverse Seesaw (while complying with charge lepton flavour violation and other electroweak precision tests). We also discuss the probing power of the considered observables in view of the expected improvement in experimental precision at FCC-ee.

hep-ph↗

arXiv2022

LFV Higgs and $Z$-boson decays: leptonic CPV phases and CP asymmetries

Heavy neutral leptons are motivated by several extensions of the Standard Model and their presence induces modifications in the lepton mixing matrix, including new Dirac and Majorana CP violating phases. It has been recently shown that these phases play an important role in lepton number and lepton flavour violating decays and transitions, with a striking impact for the predicted rates of certain observables. In this work, we now consider the potential role of the heavy neutral fermions and of the new CP violating phases in Higgs and $Z$-boson lepton flavour violating decays $H,Z\to \ell_α^\pm\ell_β^\mp$, as well as in the corresponding CP asymmetries. In order to allow for a thorough analysis, we derive the full analytical expressions of the latter observables, taking into account the effect of the (final state) charged lepton masses. A comprehensive exploration of lepton flavour violating $Z$ and Higgs decays confirms that these are very sensitive to the presence of the additional heavy neutral leptons. Moreover, the new CPV phases have a clear impact on the decay rates, leading to both destructive and constructive interferences. Interestingly, in the $μτ$ sector, the $Z\to \ell_α^\pm\ell_β^\mp$ rates are within reach of FCC-ee, with associated CP asymmetries that can potentially reach up to $20\% - 30\%$.

hep-ph↗

arXiv2022

The European Spallation Source neutrino Super Beam Conceptual Design Report

This conceptual design report provides a detailed account of the European Spallation Source neutrino Super Beam (ESS$ν$SB) feasibility study. This facility has been proposed after the measurements reported in 2012 of a relatively large value of the neutrino mixing angle $θ_{13}$, which raised the possibility of observing potential CP violation in the leptonic sector with conventional neutrino beams. The measured value of $θ_{13}$ also privileges the $2^{nd}$ oscillation maximum for the discovery of CP violation instead of the more typically studied $1^{st}$ maximum. The sensitivity at this $2^{nd}$ oscillation maximum is about three times higher than at the $1^{st}$ one, which implies a reduced influence of systematic errors. Working at the $2^{nd}$ oscillation maximum requires a very intense neutrino beam with an appropriate energy. The world's most intense pulsed spallation neutron source, the European Spallation Source (ESS), will have a proton linac operating at 5\,MW power, 2\,GeV kinetic energy and 14~Hz repetition rate (3~ms pulse duration, 4\% duty cycle) for neutron production. In this design study it is proposed to double the repetition rate and compress the beam pulses to the level of microseconds in order to provide an additional 5~MW proton beam for neutrino production. The physics performance has been evaluated for such a neutrino super beam, in conjunction with a megaton-scale underground water Cherenkov neutrino detector installed at a distance of 360--550\,km from ESS. The ESS proton linac upgrades, the accumulator ring required for proton-pulse compression, the target station design and optimisation, the near and far detector complexes, and the physics potential of the facility are all described in this report. The ESS linac will be operational by 2025, at which point the implementation of upgrades for the neutrino facility could begin.

hep-ex↗

arXiv2022

The European Spallation Source neutrino Super Beam

In this Snowmass 2021 white paper, we summarise the Conceptual Design of the European Spallation Source neutrino Super Beam (ESSvSB) experiment and its synergies with the possible future muon based facilities, e.g. a Low Energy nuSTORM and the Muon Collider. The ESSvSB will benefit from the high power, 5 MW, of the European Spallation Source (ESS) LINAC in Lund-Sweden to produce the world most intense neutrino beam, enabling measurements to be made at the second oscillation maximum. Assuming a ten-year exposure, physics simulations show that the CP-invariance violation can be established with a significance of 5 sigma over more than 70% of all values of delta CP and with an error in the measurement of the delta CP angle of less than 8 degree for all values of delta CP. However, several technological and physics challenges must be further studied before achieving a final Technical Design. Measuring at the 2nd oscillation maximum necessitates a very intense neutrino beam with the appropriate energy. For this, the ESS proton beam LINAC, which is designed to produce the world's most intense neutron beam, will need to be upgraded to 10 MW power, 2.5 GeV energy and 28 Hz beam pulse repetition rate. An accumulator ring will be required for the compression of the ESS LINAC beam pulse from 2.86 ms to 1.3 mus. A high power target station facility will be needed to produce a well-focused intense (super) mu-neutrino beam. The physics performance of that neutrino Super Beam in conjunction with a megaton underground Water Cherenkov neutrino far detector installed at a distance of either 360 km or 540 km from the ESS, the baseline, has been evaluated.

physics.acc-ph↗

arXiv2021

Updated physics performance of the ESSnuSB experiment

In this paper, we present the physics performance of the ESSnuSB experiment in the standard three flavor scenario using the updated neutrino flux calculated specifically for the ESSnuSB configuration and updated migration matrices for the far detector. Taking conservative systematic uncertainties corresponding to a normalization error of $5\%$ for signal and $10\%$ for background, we find that there is $10σ$ $(13σ)$ CP violation discovery sensitivity for the baseline option of 540 km (360 km) at $δ_{\rm CP} = \pm 90^\circ$. The corresponding fraction of $δ_{\rm CP}$ for which CP violation can be discovered at more than $5 σ$ is $70\%$. Regarding CP precision measurements, the $1σ$ error associated with $δ_{\rm CP} = 0^\circ$ is around $5^\circ$ and with $δ_{\rm CP} = -90^\circ$ is around $14^\circ$ $(7^\circ)$ for the baseline option of 540 km (360 km). For hierarchy sensitivity, one can have $3σ$ sensitivity for 540 km baseline except $δ_{\rm CP} = \pm 90^\circ$ and $5σ$ sensitivity for 360 km baseline for all values of $δ_{\rm CP}$. The octant of $θ_{23}$ can be determined at $3 σ$ for the values of: $θ_{23} > 51^\circ$ ($θ_{23} < 42^\circ$ and $θ_{23} > 49^\circ$) for baseline of 540 km (360 km). Regarding measurement precision of the atmospheric mixing parameters, the allowed values at $3 σ$ are: $40^\circ < θ_{23} < 52^\circ$ ($42^\circ < θ_{23} < 51.5^\circ$) and $2.485 \times 10^{-3}$ eV$^2 < Δm^2_{31} < 2.545 \times 10^{-3}$ eV$^2$ ($2.49 \times 10^{-3}$ eV$^2 < Δm^2_{31} < 2.54 \times 10^{-3}$ eV$^2$) for the baseline of 540 km (360 km).

hep-ex↗

arXiv2021

The physics potential of a reactor neutrino experiment with Skipper-CCDs: Searching for new physics with light mediators

We explore the sensitivity to new physics of the recently proposed vIOLETA experiment: a 10 kg Skipper Charged Coupled Device detector deployed 12 meters away from a commercial nuclear reactor core. We investigate two broad classes of models which benefit from the very low energy recoil threshold of these detectors, namely neutrino magnetic moments and light mediators coupled to neutrinos and quarks or electrons. We find that this experimental setup is very sensitive to light, weakly coupled new physics, and in particular that it could probe potential explanations of the event excess observed in XENON1T. We also provide a detailed study on the dependence of the sensitivity on the experimental setup assumptions and on the neutrino flux systematic uncertainties.

hep-ph↗

arXiv2021

$ν$ Electroweak Baryogenesis

We investigate if the CP violation necessary for successful electroweak baryogenesis may be sourced by the neutrino Yukawa couplings. In particular, we consider an electroweak scale Seesaw realisation with sizeable Yukawas where the new neutrino singlets form (pseudo)-Dirac pairs. We find that flavour effects critically impact the final asymmetry obtained and that, taking them into account, the observed value may be obtained in some regions of the parameter space. This source of CP violation naturally avoids the strong constraints from electric dipole moments and links the origin of the baryon asymmetry of the Universe with the mechanism underlying neutrino masses. Interestingly, the mixing of the active and heavy neutrinos needs to be sizeable and could be probed at the LHC or future collider experiments.

hep-ph↗

arXiv2020

$ν$ Electroweak Baryogenesis

We investigate if the CP violation necessary for successful electroweak baryogenesis may be sourced by the neutrino Yukawa couplings. In particular, we consider an electroweak scale Seesaw realization with sizable Yukawas where the new neutrino singlets form (pseudo)-Dirac pairs, as in the linear or inverse Seesaw variants. We find that the baryon asymmetry obtained strongly depends on how the neutrino masses vary within the bubble walls. Moreover, we also find that flavour effects critically impact the final asymmetry obtained and that, taking them into account, the observed value may be obtained in some regions of the parameter space. This source of CP violation naturally avoids the strong constraints from electric dipole moments and links the origin of the baryon asymmetry of the Universe with the mechanism underlying neutrino masses. Interestingly, the mixing of the active and heavy neutrinos needs to be sizable and could be probed at the LHC or future collider experiments.

hep-ph↗

arXiv2020

Physics potential of the ESS$ν$SB

The ESS$ν$SB project proposes to base a neutrino ''Super Beam'' of unprecedented luminosity at the European Spallation Source. The original proposal identified the second peak of the oscillation probability as the optimal to maximize the discovery potential to leptonic CP violation. However this choice reduces the statistics at the detector and penalizes other complementary searches such as the determination of the atmospheric oscillation parameters, particularly the octant of $θ_{23}$ as well as the neutrino mass ordering. We explore how these shortcomings can be alleviated by the combination of the beam data with the atmospheric neutrino sample that would also be collected at the detector. We find that the combination not only improves very significantly these drawbacks, but also enhances both the CP violation discovery potential and the precision in the measurement of the CP violating phase, for which the facility was originally optimized, by lifting parametric degeneracies. We then reassess the optimization of the ESS$ν$SB setup when the atmospheric neutrino sample is considered, with an emphasis in performing a measurement of the CP violating phase as precise as possible. We find that for the presently preferred value of $δ\sim -π/2$, shorter baselines and longer running time in neutrino mode would be optimal. In these conditions, a measurement better than $14^\circ$ would be achievable for any value of the $θ_{23}$ octant and the mass ordering. Conversely, if present and next generation facilities were not able to discover CP violation, longer baselines and more even splitting between neutrino and neutrino modes would be preferable. These choices would allow a $5 σ$ discovery of CP violation for around a $60\%$ of the possible values of $δ$ and to determine its value with a precision around $6^\circ$ if it is close to $0$ or $π$.

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