
NEXT Collaboration(Simon, A. et al), GomezCadenas, J. J., Alvarez, V., BenllochRodriguez, J. M., Botas, A., Carcel, S., et al. (2017). Application and performance of an MLEM algorithm in NEXT. J. Instrum., 12, P08009–22pp.
Abstract: The goal of the NEXT experiment is the observation of neutrinoless double beta decay in Xe136 using a gaseous xenon TPC with electroluminescent amplification and specialized photodetector arrays for calorimetry and tracking. The NEXT Collaboration is exploring a number of reconstruction algorithms to exploit the full potential of the detector. This paper describes one of them: the Maximum Likelihood Expectation Maximization (MLEM) method, a generic iterative algorithm to find maximumlikelihood estimates of parameters that has been applied to solve many different types of complex inverse problems. In particular, we discuss a bidimensional version of the method in which the photosensor signals integrated over time are used to reconstruct a transverse projection of the event. First results show that, when applied to detector simulation data, the algorithm achieves nearly optimal energy resolution (better than 0.5% FWHM at the Q value of 136Xe) for events distributed over the full active volume of the TPC.
Keywords: Gaseous imaging and tracking detectors; Image reconstruction in medical imaging; Time projection Chambers (TPC); Medicalimage reconstruction methods and algorithms; computeraided software


De Romeri, V., FernandezMartinez, E., Gehrlein, J., Machado, P. A. N., & Niro, V. (2017). Dark Matter and the elusive Z' in a dynamical Inverse Seesaw scenario. J. High Energy Phys., 10(10), 169–21pp.
Abstract: The Inverse Seesaw naturally explains the smallness of neutrino masses via an approximate BL symmetry broken only by a correspondingly small parameter. In this work the possible dynamical generation of the Inverse Seesaw neutrino mass mechanism from the spontaneous breaking of a gauged U(1) BL symmetry is investigated. Interestingly, the Inverse Seesaw pattern requires a chiral content such that anomaly cancellation predicts the existence of extra fermions belonging to a dark sector with large, nontrivial, charges under the U(1) BL. We investigate the phenomenology associated to these new states and find that one of them is a viable dark matter candidate with mass around the TeV scale, whose interaction with the Standard Model is mediated by the Z' boson associated to the gauged U(1) BL symmetry. Given the large charges required for anomaly cancellation in the dark sector, the BL Z' interacts preferentially with this dark sector rather than with the Standard Model. This suppresses the rate at direct detection searches and thus alleviates the constraints on Z'mediated dark matter relic abundance. The collider phenomenology of this elusive Z' is also discussed.
Keywords: Beyond Standard Model; Neutrino Physics


Garcia Canal, C. A., Tarutina, T., & Vento, V. (2017). Deuteron structure in the deep inelastic regime. Eur. Phys. J. A, 53(6), 118–5pp.
Abstract: We study nuclear effects in the deuteron in the deep inelastic regime using the newest available data. We put special emphasis on their Q(2) dependence. The study is carried out using a scheme which parameterizes, in a simple manner, these effects by changing the proton and neutron stucture functions in medium. The result of our analysis is compared with other recent proposals. We conclude that precise EMC ratios cannot be obtained without considering the nuclear effects in the deuteron.


Alfonso, V. I., Bejarano, C., Beltran Jimenez, J., Olmo, G. J., & Orazi, E. (2017). The trivial role of torsion in projective invariant theories of gravity with nonminimally coupled matter fields. Class. Quantum Gravity, 34(23), 235003–20pp.
Abstract: We study a large family of metricaffine theories with a projective symmetry, including nonminimally coupled matter fields which respect this invariance. The symmetry is straightforwardly realised by imposing that the connection only enters through the symmetric part of the Ricci tensor, even in the matter sector. We leave the connection completely free (including torsion), and obtain its general solution as the LeviCivita connection of an auxiliary metric, showing that the torsion only appears as a projective mode. This result justifies the widely used condition of setting vanishing torsion in these theories as a simple gauge choice. We apply our results to some particular cases considered in the literature, including the socalled EddingtoninspiredBornInfeld theories among others. We finally discuss the possibility of imposing a gauge fixing where the connection is metric compatible, and comment on the genuine character of the nonmetricity in theories where the two metrics are not conformally related.
Keywords: modified gravity; metricaffine theories; torsion; nonminimal couplings


Agullo, I., del Rio, A., & NavarroSalas, J. (2017). Gravity and handedness of photons. Int. J. Mod. Phys. D, 26(12), 1742001–5pp.
Abstract: Vacuum fluctuations of quantum fields are altered in the presence of a strong gravitational background, with important physical consequences. We argue that a nontrivial spacetime geometry can act as an optically active medium for quantum electromagnetic radiation, in such a way that the state of polarization of radiation changes in time, even in the absence of electromagnetic sources. This is a quantum effect, and is a consequence of an anomaly related to the classical invariance under electricmagnetic duality rotations in Maxwell theory.
Keywords: Quantum fields in curved spacetime; symmetry and conservation laws; electromagnetic wave propagation; anomalies


