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Hernandez, P., Kekic, M., & Lopez-Pavon, J. (2014). N_eff in low-scale seesaw models versus the lightest neutrino mass. Phys. Rev. D, 90(6), 065033–12pp.
Abstract: We evaluate the contribution to N_eff of the extra sterile states in low-scale type I seesaw models (with three extra sterile states). We explore the full parameter space and find that at least two of the heavy states always reach thermalization in the early Universe, while the third one might not thermalize provided the lightest neutrino mass is below O(10(-3) eV). Constraints from cosmology therefore severely restrict the spectra of heavy states in the range 1 eV-100 MeV. The implications for neutrinoless double beta decay are also discussed.
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Herrera-Aguilar, A., Rojas, A. D., & Santos, E. (2014). Localization of gauge fields in a tachyonic de Sitter thick braneworld. Eur. Phys. J. C, 74(4), 2770–6pp.
Abstract: In this work we show that universal gauge vector fields can be localized on the recently proposed 5D thick tachyonic braneworld which involves a de Sitter cosmological background induced on the 3-brane. Namely, by performing a suitable decomposition of the vector field, the resulting 4D effective action corresponds to a massive gauge field, while the profile along the extra dimension obeys a Schrodinger-like equation with a Poschl-Teller potential. It turns out that the massless zero mode of the gauge field is bound to the expanding 3-brane and allows us to recover the standard 4D electromagnetic phenomena of our world. Moreover, this zero mode is separated from the continuum of Kaluza-Klein (KK) modes by a mass gap determined by the scale of the expansion parameter. We also were able to analytically solve the corresponding Schrodinger-like equation for arbitrary mass, showing that KK massive modes asymptotically behave like plane waves, as expected.
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Herrero-Garcia, J., Nebot, M., Rius, N., & Santamaria, A. (2014). The Zee-Babu model revisited in the light of new data. Nucl. Phys. B, 885, 542–570.
Abstract: We update previous analyses of the Zee-Babu model in the light of new data, e.g., the mixing angle On, the rare decay μ-> e gamma and the LHC results. We also analyze the possibility of accommodating the deviations in Gamma (H -> gamma gamma) hinted by the LHC experiments, and the stability of the scalar potential. We find that neutrino oscillation data and low energy constraints are still compatible with masses of the extra charged scalars accessible to LHC. Moreover, if any of them is discovered, the model can be falsified by combining the information on the singly and doubly charged scalar decay modes with neutrino data. Conversely, if the neutrino spectrum is found to be inverted and the CP phase delta is quite different from pi, the masses of the charged scalars will be well outside the LHC reach.
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Hinarejos, M., Di Franco, C., Romanelli, A., & Perez, A. (2014). Chirality asymptotic behavior and non-Markovianity in quantum walks on a line. Phys. Rev. A, 89(5), 052330–7pp.
Abstract: We investigate the time evolution of the chirality reduced density matrix for a discrete-time quantum walk on a one-dimensional lattice. The matrix is obtained by tracing out the spatial degree of freedom. We analyze the standard case, without decoherence, and the situation in which decoherence appears in the form of broken links in the lattice. By examining the trace distance for possible pairs of initial states as a function of time, we conclude that the evolution of the reduced density matrix is non-Markovian, in the sense defined by Breuer, Laine, and Piilo [Phys. Rev. Lett. 103, 210401 (2009)]. As the level of noise increases, the dynamics approaches a Markovian process. The highest non-Markovianity corresponds to the case without decoherence. The reduced density matrix tends always to a well-defined limit that we calculate, but only in the decoherence-free case is this limit nontrivial.
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Ilisie, V., & Pich, A. (2014). Low-mass fermiophobic charged Higgs phenomenology in two-Higgs-doublet models. J. High Energy Phys., 09(9), 089–32pp.
Abstract: After the recent discovery of a Higgs-like boson, the possibility of an enlarged scalar sector arises as a natural question. Experimental searches for charged scalars have been already performed with negative results. We analyze the phenomenology associated with a fermiophobic charged Higgs (it does not couple to fermions at tree level), in two-Higgs-doublet models. All present experimental bounds are evaded trivially in this case, and one needs to consider other decay and production channels. We study the associated production of a charged Higgs with either a W or a neutral scalar boson, and the relevant decays for a light fermiophobic charged Higgs. The interesting features of this scenario should result encouraging for the LHC collaborations to perform searches for such a particle.
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Jones Perez, J. (2014). Split-family SUSY, U(2)(5) flavour symmetry and neutrino physics. Eur. Phys. J. C, 74(2), 2772–9pp.
Abstract: In split-family SUSY, one can use a U(2)(3) symmetry to protect flavour observables in the quark sector from SUSY contributions. However, attempts to extend this procedure to the lepton sector by using an analogous U(2)(5) symmetry fail to reproduce the neutrino data without introducing some form of fine-tuning. In this work, we solve this problem by shifting the U(2)(2) symmetry acting on leptons towards the second and third generations. This allows neutrino data to be reproduced without much difficulties, as well as protecting the leptonic flavour observables from SUSY. Key signatures are a μ-> e gamma branching ratio possibly observable in the near future, as well as having selectrons as the lightest sleptons.
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Jung, M., & Pich, A. (2014). Electric dipole moments in two-Higgs-doublet models. J. High Energy Phys., 04(4), 076–42pp.
Abstract: Electric dipole moments are extremely sensitive probes for additional sources of CP violation in new physics models. Specifically, they have been argued in the past to exclude new CP-violating phases in two-Higgs-doublet models. Since recently models including such phases have been discussed widely, we revisit the available constraints in the presence of mechanisms which are typically invoked to evade flavour-changing neutral currents. To that aim, we start by assessing the necessary calculations on the hadronic, nuclear and atomic/molecular level, deriving expressions with conservative error estimates. Their phenomenological analysis in the context of two-Higgs-doublet models yields strong constraints, in some cases weakened by a cancellation mechanism among contributions from neutral scalars. While the corresponding parameter combinations do not yet have to be unnaturally small, the constraints are likely to preclude large effects in other CP-violating observables. Nevertheless, the generically expected contributions to electric dipole moments in this class of models lie within the projected sensitivity of the next-generation experiments.
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Juste, A., Mantry, S., Mitov, A., Penin, A., Skands, P., Varnes, E., et al. (2014). Determination of the top quark mass circa 2013: methods, subtleties, perspectives. Eur. Phys. J. C, 74(10), 3119–14pp.
Abstract: We present an up-to-date overview of the problem of top quark mass determination. We assess the need for precision in the top mass extraction in the LHC era together with the main theoretical and experimental issues arising in precision top mass determination. We collect and document existing results on top mass determination at hadron colliders and map the prospects for future precision top mass determination at e(+)e(-) colliders. We present a collection of estimates for the ultimate precision of various methods for top quark mass extraction at the LHC.
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Karakoc, M. et al, & Molina, F. (2014). Gamow-Teller transitions in the A=40 isoquintet of relevance for neutrino captures in Ar-40. Phys. Rev. C, 89(6), 064313–7pp.
Abstract: Background: The Gamow-Teller response of Ar-40 is important for the use of liquid argon as a medium for neutrino detection. An ambiguity about the Gamow-Teller strength for the excitation of 1(+) states at 2290 and 2730 keV in K-40 results in a significant uncertainty for neutrino capture rates. This ambiguity is caused by the large discrepancy observed between strengths extracted from Ar-40(p, n) charge-exchange data and the transition strengths for the analog transitions studied in the beta decay of Ti-40. Purpose: This study was aimed at resolving the ambiguity between the results from the Ar-40(p, n) charge-exchange and Ti-40 beta-decay data. Method: Shell-model calculations in the sd-pf shell with a new interaction (WBMB-C) were used to study differences between the structure of the transitions from Ar-40 and Ti-40. Distorted-wave Born approximation reaction calculations were used to investigate uncertainties in the extraction of Gamow-Teller strength from the Ar-40(p, n) data. New high-resolution data for the Ar-40(He-3,t) reaction were used to gain further insight into the charge-exchange reaction mechanism and to provide more information to test the validity of the shell-model calculations. Results: The shell-model calculations showed that interference between amplitudes associated with pf and sd components to the low-lying Gamow-Teller transitions, in combination with a difference in Coulomb energy shifts for Ar-40 and Ti-40, can produce the differences on the scale of those observed between the Ar-40 charge-exchange and Ti-40 beta-decay data. In combination with the difference in nuclear penetrability of the (p, n) and (He-3,t) probes, the different contributions from amplitudes associated with transitions in the pf and sd shells are likely also responsible for the observed discrepancy between the ratio of the cross sections for the low-lying 1(+) states in the Ar-40(p, n) and Ar-40(He-3,t) data. Conclusions: On the basis of this study, it is recommended to use Gamow-Teller strengths extracted from the Ar-40(p, n) data, not the Ti-40 beta-decay data, for the calculation of neutrino capture rates. Further theoretical studies are required to achieve a consistent quantitative description for the energy differences between low-lying 1(+) states in K-40 and Sc-40 and the experimentally observed Gamow-Teller strengths.
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Kersten, J., Park, J. H., Stockinger, D., & Velasco-Sevilla, L. (2014). Understanding the correlation between (g-2)(mu) and μ-> e gamma in the MSSM. J. High Energy Phys., 08(8), 118–32pp.
Abstract: The supersymmetric contributions to the muon anomalous magnetic moment a and to the decay μ-> e gamma are given by very similar Feynman diagrams. Previous works reported correlations in specific scenarios, in particular if alpha(mu) is dominated by a single diagram. In this work we give an extensive survey of the possible correlations. We discuss examples of single-diagram domination with particularly strong correlations, and provide corresponding benchmark parameter points. We show how the correlations are weakened by significant cancellations between diagrams in large parts of the MSSM parameter space. Nevertheless, the order of magnitude of BR(mu -> e gamma) for a fixed flavor-violating parameter can often be predicted. We summarize the behavior by plotting the correlations as well as resulting bounds on the flavor-violating parameters under various assumptions on the MSSM spectrum.
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