
Aristizabal Sierra, D., Bazzocchi, F., de Medeiros Varzielas, I., Merlo, L., & Morisi, S. (2010). Tri/Bimaximal lepton mixing and leptogenesis. Nucl. Phys. B, 827(12), 34–58.
Abstract: In models with flavour symmetries added to the gauge group of the Standard Model the CPviolating asymmetry necessary for leptogenesis may be related with lowenergy parameters. A particular case of interest is when the flavour symmetry produces exact Tri/Bimaximal lepton mixing leading to a vanishing CPviolating asymmetry. In this paper we present a modelindependent discussion that confirms this always occurs for unflavoured leptogenesis in type I seesaw scenarios, noting however that Tri/Bimaximal mixing does not imply a vanishing asymmetry in general scenarios where there is interplay between type I and other seesaws. We also consider a specific model where the exact Tri/Bimaximal mixing is lifted by corrections that can be parametrised by a small number of degrees of freedom and analyse in detail the existing link between low and highenergy parameters – focusing on how the deviations from Tri/Bimaximal are connected to the parameters governing leptogenesis.



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.



Aristizabal Sierra, D., Degee, A., Dorame, L., & Hirsch, M. (2015). Systematic classification of twoloop realizations of the Weinberg operator. J. High Energy Phys., 03(3), 040–41pp.
Abstract: We systematically analyze the d = 5 Weinberg operator at 2loop order. Using a diagrammatic approach, we identify two different interesting categories of neutrino mass models: (i) Genuine 2loop models for which both, treelevel and 1loop contributions, are guaranteed to be absent. And (ii) finite 2loop diagrams, which correspond to the 1loop generation of some particular vertex appearing in a given 1loop neutrino mass model, thus being effectively 2loop. From the large list of all possible 2loop diagrams, the vast majority are infinite corrections to lower order neutrino mass models and only a moderately small number of diagrams fall into these two interesting classes. Moreover, all diagrams in class (i) are just variations of three basic diagrams, with examples discussed in the literature before. Similarly, we also show that class (ii) diagrams consists of only variations of these three plus two more basic diagrams. Finally, we show how our results can be consistently and readily used in order to construct twoloop neutrino mass models.



Aristizabal Sierra, D., HerreroGarcia, J., Restrepo, D., & Vicente, A. (2016). Diboson anomaly: Heavy Higgs resonance and QCD vectorlike exotics. Phys. Rev. D, 93(1), 015012–12pp.
Abstract: The ATLAS Collaboration (and also CMS) has recently reported an excess over Standard Model expectations for gauge boson pair production in the invariant mass region 1.82.2 TeV. In light of these results, we argue that such a signal might be the first manifestation of the production and further decay of a heavy CPeven Higgs resulting from a typeI two Higgs doublet model. We demonstrate that in the presence of colored vectorlike fermions, its gluon fusion production cross section is strongly enhanced, with the enhancement depending on the color representation of the new fermion states. Our findings show that barring the color triplet case, any QCD “exotic” representation can fit the ATLAS result in fairly large portions of the parameter space. We have found that if the diboson excess is confirmed and this mechanism is indeed responsible for it, then the LHC Run2 should find (i) a CPodd scalar with mass below similar to 2.3 TeV, (ii) new colored states with masses below similar to 2 TeV, (iii) no statistically significant diboson events in the W(+/)Z channel, (iv) events in the triboson channels W(+/)W(/+)Z and ZZZ with invariant mass amounting to the mass of the CPodd scalar.



Aristizabal Sierra, D., Staub, F., & Vicente, A. (2015). Shedding light on the b > s anomalies with a dark sector. Phys. Rev. D, 92(1), 015001–11pp.
Abstract: The LHCb Collaboration has recently reported on some anomalies in b > s transitions. In addition to discrepancies with the Standard Model (SM) predictions in some angular observables and branching ratios, an intriguing hint for lepton universality violation was found. Here we propose a simple model that extends the SM with a dark sector charged under an additional U(1) gauge symmetry. The spontaneous breaking of this symmetry gives rise to a massive Z' boson, which communicates the SM particles with a valid dark matter candidate, while solving the b > s anomalies with contributions to the relevant observables.



Aristizabal Sierra, D., Tortola, M., Valle, J. W. F., & Vicente, A. (2014). Leptogenesis with a dynamical seesaw scale. J. Cosmol. Astropart. Phys., 07(7), 052–20pp.
Abstract: In the simplest typeI seesaw leptogenesis scenario righthanded neutrino annihilation processes are absent. However, in the presence of new interactions these processes are possible and can affect the resulting B – L asymmetry in an important way. A prominent example is provided by models with spontaneous lepton number violation, where the existence of new dynamical degrees of freedom can play a crucial role. In this context, we provide a modelindependent discussion of the effects of righthanded neutrino annihilations. We show that in the weak washout regime, as long as the scattering processes remain slow compared with the Hubble expansion rate throughout the relevant temperature range, the efficiency can be largely enhanced, reaching in some cases maximal values. Moreover, the B – L asymmetry yield turns out to be independent upon initial conditions, in contrast to the “standard” case. On the other hand, when the annihilation processes are fast, the righthanded neutrino distribution tends to a thermal one down to low temperatures, implying a drastic suppression of the efficiency which in some cases can render the B – L generation mechanism inoperative.

