
Abada, A., De Romeri, V., Lucente, M., Teixeira, A. M., & Toma, T. (2018). Effective Majorana mass matrix from tau and pseudoscalar meson lepton number violating decays. J. High Energy Phys., 02(2), 169–57pp.
Abstract: An observation of any lepton number violating process will undoubtedly point towards the existence of new physics and indirectly to the clear Majorana nature of the exchanged fermion. In this work, we explore the potential of a minimal extension of the Standard Model via heavy sterile fermions with masses in the [0.110] GeV range concerning an extensive array of “neutrinoless” meson and tau decay processes. We assume that the Majorana neutrinos are produced onshell, and focus on threebody decays. We conduct an update on the bounds on the activesterile mixing elements, vertical bar Ul alpha 4,Ul beta 4 vertical bar, taking into account the most recent experimental bounds (and constraints) and new theoretical inputs, as well as the effects of a finite detector, imposing that the heavy neutrino decay within the detector. This allows to establish uptodate comprehensive constraints on the sterile fermion parameter space. Our results suggest that the branching fractions of several decays are close to current sensitivities (likely within reach of future facilities), some being already in conflict with current data (as is the case of Kbroken vertical bar > l(alpha)(broken vertical bar)+l(beta)(+)pi(), and tau()>mu(broken vertical bar)pi()pi()). We use these processes to extract constraints on all entries of an enlarged definition of a 3 x 3 “effective” Majorana neutrino mass matrix m(v)(alpha beta).



Anamiati, G., De Romeri, V., Hirsch, M., Ternes, C. A., & Tortola, M. (2019). QuasiDirac neutrino oscillations at DUNE and JUNO. Phys. Rev. D, 100(3), 035032–12pp.
Abstract: QuasiDirac neutrinos are obtained when the Lagrangian density of a neutrino mass model contains both Dirac and Majorana mass terms, and the Majorana terms are sufficiently small. This type of neutrino introduces new mixing angles and mass splittings into the Hamiltonian, which will modify the standard neutrino oscillation probabilities. In this paper, we focus on the case where the new mass splittings are too small to be measured, but new angles and phases are present. We perform a sensitivity study for this scenario for the upcoming experiments DUNE and JUNO, finding that they will improve current bounds on the relevant parameters. Finally, we also explore the discovery potential of both experiments, assuming that neutrinos are indeed quasiDirac particles.



Aristizabal Sierra, D., De Romeri, V., Flores, L. J., & Papoulias, D. K. (2020). Light vector mediators facing XENON1T data. Phys. Lett. B, 809, 135681–5pp.
Abstract: Recently the XENON1T collaboration has released new results on searches for new physics in lowenergy electronic recoils. The data shows an excess over background in the lowenergy tail, particularly pronounced at about 23 keV. With an exposure of 0.65 tonneyear, large detection efficiency and energy resolution, the detector is sensitive as well to solar neutrino backgrounds, with the most prominent contribution given by pp neutrinos. We investigate whether such signal can be explained in terms of new neutrino interactions with leptons mediated by a light vector particle. We find that the excess is consistent with this interpretation for vector masses below less than or similar to 0.1 MeV. The region of parameter space probed by the XENON1T data is competitive with constraints from laboratory experiments, in particular GEMMA, Borexino and TEXONO. However we point out a severe tension with astrophysical bounds and cosmological observations.



Aristizabal Sierra, D., De Romeri, V., & Papoulias, D. K. (2022). Consequences of the DresdenII reactor data for the weak mixing angle and new physics. J. High Energy Phys., 09(9), 076–22pp.
Abstract: The DresdenII reactor experiment has recently reported a suggestive evidence for the observation of coherent elastic neutrinonucleus scattering, using a germanium detector. Given the low recoil energy threshold, these data are particularly interesting for a lowenergy determination of the weak mixing angle and for the study of new physics leading to spectral distortions at low momentum transfer. Using two hypotheses for the quenching factor, we study the impact of the data on: (i) The weak mixing angle at a renormalization scale of similar to 10 MeV, (ii) neutrino generalized interactions with light mediators, (iii) the sterile neutrino dipole portal. The results for the weak mixing angle show a strong dependence on the quenching factor choice. Although still with large uncertainties, the DresdenII data provide for the first time a determination of sin(2)theta(W) at such scale using coherent elastic neutrinonucleus scattering data. Tight upper limits are placed on the light vector, scalar and tensor mediator scenarios. Kinematic constraints implied by the reactor antineutrino flux and the ionization energy threshold allow the sterile neutrino dipole portal to produce upscattering events with sterile neutrino masses up to similar to 8 MeV. In this context, we find that limits are also sensitive to the quenching factor choice, but in both cases competitive with those derived from XENON1T data and more stringent that those derived with COHERENT data, in the same sterile neutrino mass range.



Aristizabal Sierra, D., De Romeri, V., & Rojas, N. (2018). COHERENT analysis of neutrino generalized interactions. Phys. Rev. D, 98(7), 075018–14pp.
Abstract: Effective neutrinoquark generalized interactions are entirely determined by Lorentz invariance, so they include all possible fourfermion nonderivative Lorentz structures. They contain neutrinoquark nonstandard interactions as a subset, but span over a larger set that involves effective scalar, pseudoscalar, axial and tensor operators. Using recent COHERENT data, we derive constraints on the corresponding couplings by considering scalar, vector and tensor quark currents and assuming no lepton flavor dependence. We allow for mixed neutrinoquark Lorentz couplings and consider two types of scenarios in which: (i) one interaction at the nuclear level is present at a time, (ii) two interactions are simultaneously present. For scenarios (i) our findings show that scalar interactions are the most severely constrained, in particular for pseudoscalarscalar neutrinoquark couplings. In contrast, tensor and nonstandard vector interactions still enable for sizable effective parameters. We find as well that an extra vector interaction improves the data fit when compared with the result derived assuming only the standard model contribution. In scenarios (ii) the presence of two interactions relaxes the bounds and opens regions in parameter space that are otherwise closed, with the effect being more pronounced in the scalarvector and scalartensor cases. We point out that barring the vector case, our results represent the most stringent bounds on effective neutrinoquark generalized interactions for mediator masses of order similar to 1 GeV. They hold as well for larger mediator masses, case in which they should be compared with limits from neutrino deepinelastic scattering data.



Aristizabal Sierra, D., De Romeri, V., & Ternes, C. A. (2024). Reactor neutrino background in nextgeneration dark matter detectors. Phys. Rev. D, 109(11), 115026–7pp.
Abstract: Third generation dark matter detectors will be fully sensitive to the 8 B solar neutrino flux. Because of this, the characterization of such a background has been the subject of extensive analyses over the last few years. In contrast, little is known about the impact of reactor neutrinos. In this paper, we report on the implications of such a flux for dark matter direct detection searches. We consider five potential detector deployment sites envisioned by the recently established XLZD Consortium: SURF, SNOLAB, Kamioka, LNGS, and Boulby. By using public reactor data, we construct five reactor clusters involving about 100 currently operating commercial nuclear reactors each and determine the net neutrino flux at each detector site. Assuming a xenon based detector and a 50 ton year exposure, we show that in all cases the neutrino event rate may be sizable, depending on energy recoil thresholds. Of all possible detector sites, SURF and LNGS are those with the smallest reactor neutrino background. On the contrary, SNOLAB and Boulby are subject to the strongest reactor neutrino fluxes, with Kamioka being subject to a more moderate background. Our findings demonstrate that reactor neutrino fluxes should be taken into account in the next round of dark matter searches. We argue that this background may be particularly relevant for directional detectors, provided they meet the requirements we have employed in this analysis.



Avila, I. M., De Romeri, V., Duarte, L., & Valle, J. W. F. (2020). Phenomenology of scotogenic scalar dark matter. Eur. Phys. J. C, 80(10), 908–19pp.
Abstract: We reexamine the minimal Singlet + Triplet Scotogenic Model, where dark matter is the mediator of neutrino mass generation. We assume it to be a scalar WIMP, whose stability follows from the same Z(2) symmetry that leads to the radiative origin of neutrino masses. The scheme is the minimal one that allows for solar and atmospheric mass scales to be generated. We perform a full numerical analysis of the signatures expected at dark matter as well as collider experiments. We identify parameter regions where dark matter predictions agree with theoretical and experimental constraints, such as neutrino oscillations, Higgs data, dark matter relic abundance and direct detection searches. We also present forecasts for near future direct and indirect detection experiments. These will further probe the parameter space. Finally, we explore collider signatures associated with the mono jet channel at the LHC, highlighting the existence of a viable light dark matter mass range.



Balaudo, A., Calore, F., De Romeri, V., & Donato, F. (2024). NAJADS: a selfcontained framework for the direct determination of astrophysical Jfactors. J. Cosmol. Astropart. Phys., 02(2), 001–33pp.
Abstract: Cosmological simulations play a pivotal role in understanding the properties of the dark matter (DM) distribution in both galactic and galaxy cluster environments. The characterization of DM structures is crucial for informing indirect DM searches, aiming at the detection of the annihilation (or decay) products of DM particles. A fundamental quantity in these analyses is the astrophysical J factor. In the DM phenomenology community, J factors are typically computed through the semi analytical modelling of the DM mass distribution, which is affected by large uncertainties. With the scope of addressing and possibly reducing these uncertainties, we present NAJADS, a selfcontained framework to derive the DM J factor directly from the raw simulations data. We show how this framework can be used to compute all sky maps of the J factor, automatically accounting for the complex 3D structure of the simulated halos and for the boosting of the signal due to the density fluctuations along the line of sight. After validating our code, we present a proof of concept application of NAJADS to a realistic halo from the IllustrisTNG suite, and exploit it to make a thorough comparison between our numerical approach and traditional semi analytical methods. JCAP02(2024)001



Calore, F., De Romeri, V., & Donato, F. (2012). Conservative upper limits on WIMP annihilation cross section from FermiLAT gamma rays. Phys. Rev. D, 85(2), 023004–9pp.
Abstract: The spectrum of an isotropic extragalactic gammaray background (EGB) has been measured by the FermiLAT telescope at high latitudes. Two new models for the EGB are derived from the subtraction of unresolved point sources and extragalactic diffuse processes, which could explain from 30% to 70% of the FermiLAT EGB. Within the hypothesis that the two residual EGBs are entirely due to the annihilation of dark matter (DM) particles in the Galactic halo, we obtain stringent upper limits on their annihilation cross section. Severe bounds on a possible Sommerfeld enhancement of the annihilation cross section are set as well. Finally, we consider models for DM annihilation depending on the inverse of the velocity and associate the EGBs to photons arising from the annihilation of DM in primordial halos. Given our choices for the EGB and the minimal DM modeling, the derived upper bounds are claimed to be conservative.



Candela, P. M., De Romeri, V., Melas, P., Papoulias, D. K., & Saoulidou, N. (2024). Upscattering production of a sterile fermion at DUNE: complementarity with spallation source and direct detection experiments. J. High Energy Phys., 10(10), 032–36pp.
Abstract: We investigate the possible production of a MeVscale sterile fermion through the upscattering of neutrinos on nuclei and atomic electrons at different facilities. We consider a phenomenological model that adds a new fermion to the particle content of the Standard Model and we allow for all possible Lorentzinvariant nonderivative interactions (scalar, pseudoscalar, vector, axialvector and tensor) of neutrinos with electrons and firstgeneration quarks. We first explore the sensitivity of the DUNE experiment to this scenario, by simulating elastic neutrinoelectron scattering events in the near detector. We consider both options of a standard and a tauoptimized neutrino beams, and investigate the impact of a mobile detector that can be moved offaxis with respect to the beam. Next, we infer constraints on the typical coupling, new fermion and mediator masses from elastic neutrinoelectron scattering events induced by solar neutrinos in two current dark matter direct detection experiments, XENONnT and LZ. Under the assumption that the new mediators couple also to firstgeneration quarks, we further set constraints on the upscattering production of the sterile fermion using coherent elastic neutrinonucleus scattering data from the COHERENT experiment. Moreover, we set additional constraints assuming that the sterile fermion may decay within the detector. We finally compare our results and discuss how these facilities are sensitive to different regions of the relevant parameter space due to kinematics arguments and can hence provide complementary information on the upscattering production of a sterile fermion.

