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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Search for long-lived particles decaying to jet pairs. Eur. Phys. J. C, 75(4), 152–12pp.
Abstract: A search is presented for long-lived particles with a mass between 25 and 50 GeV/c(2) and a lifetime between 1 and 200 ps in a sample of proton-proton collisions at a centre-of-mass energy of root s = 7 TeV, corresponding to an integrated luminosity of 0.62 fb(-1), collected by the LHCb detector. The particles are assumed to be pair-produced by the decay of a standard model-like Higgs boson. The experimental signature of the long-lived particle is a displaced vertex with two associated jets. No excess above the background is observed and limits are set on the production cross-section as a function of the long-lived particle mass and lifetime.
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Vincent, A. C., Fernandez Martinez, E., Hernandez, P., Mena, O., & Lattanzi, M. (2015). Revisiting cosmological bounds on sterile neutrinos. J. Cosmol. Astropart. Phys., 04(4), 006–23pp.
Abstract: We employ state-of-the art cosmological observables including supernova surveys and BAO information to provide constraints on the mass and mixing angle of a non-resonantly produced sterile neutrino species, showing that cosmology can effectively rule out sterile neutrinos which decay between BBN and the present day. The decoupling of an additional heavy neutrino species can modify the time dependence of the Universe's expansion between BBN and recombination and, in extreme cases, lead to an additional matter-dominated period; while this could naively lead to a younger Universe with a larger Hubble parameter, it could later be compensated by the extra radiation expected in the form of neutrinos from sterile decay. However, recombination-era observables including the Cosmic Microwave Background (CMB), the shift parameter R-CMB and the sound horizon r(s) from Baryon Acoustic Oscillations (BAO) severely constrain this scenario. We self-consistently include the full time-evolution of the coupled sterile neutrino and standard model sectors in an MCMC, showing that if decay occurs after BBN, the sterile neutrino is essentially bounded by the constraint sin(2) theta less than or similar to 0.026(m(s)/eV)(-2).
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Izmaylov, A., Sorel, M., & Stamoulis, P. (2015). Neutrino oscillation physics potential of the T2K experiment. Prog. Theor. Exp. Phys., (4), 043C01–36pp.
Abstract: The observation of the recent electron neutrino appearance in a muon neutrino beam and the high-precision measurement of the mixing angle theta(13) have led to a re-evaluation of the physics potential of the T2K long-baseline neutrino oscillation experiment. Sensitivities are explored for CP violation in neutrinos, non-maximal sin(2) 2 theta(23), the octant of theta(23), and the mass hierarchy, in addition to the measurements of delta CP, sin(2) theta(23), and Delta m(32)(2), for various combinations of nu-mode and (nu) over bar -mode data-taking. With an exposure of 7.8 x 10(21) protons-on-target, T2K can achieve 1 sigma resolution of 0.050 (0.054) on sin(2) theta(23) and 0.040 (0.045) x 10(-3) eV(2) on Delta m(32)(2) for 100% (50%) neutrino beam mode running assuming sin(2) theta(23) = 0.5 and Delta m(32)(2) = 2.4 x 10(-3) eV(2). T2K will have sensitivity to the CP-violating phase delta(CP) at 90% C.L. or better over a significant range. For example, if sin(2) 2 theta(23) is maximal (i.e.theta(23) = 45 degrees) the range is -115 degrees < delta(CP) < -60 degrees for normal hierarchy and +50 degrees < delta(CP) < + 130 degrees for inverted hierarchy. When T2K data is combined with data from the NO nu A experiment, the region of oscillation parameter space where there is sensitivity to observe a non-zero delta CP is substantially increased compared to if each experiment is analyzed alone.
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Pallis, C., & Shafi, Q. (2015). Gravity waves from non-minimal quadratic inflation. J. Cosmol. Astropart. Phys., 03(3), 023–31pp.
Abstract: We discuss non-minimal quadratic inflation in supersymmetric (SUSY) and non-SUSY models which entails a linear coupling of the inflaton to gravity. Imposing a lower bound on the parameter c(R), involved in the coupling between the inflaton and the Ricci scalar curvature, inflation can be attained even for subplanckian values of the inflaton while the corresponding effective theory respects the perturbative unitarity up to the Planck scale. Working in the non-SUSY context we also consider radiative corrections to the inflationary potential due to a possible coupling of the inflaton to bosons or fermions. We find ranges of the parameters, depending mildly on the renormalization scale, with adjustable values of the spectral index n(s), tensor-to-scalar ratio r similar or equal to (2 – 4) . 10(-3), and an inflaton mass close to 3 . 10 (13) GeV. In the SUSY framework we employ two gauge singlet chiral superfields, a logarithmic Kahler potential including all the allowed terms up to fourth order in powers of the various fields, and determine uniquely the superpotential by applying a continuous R and a global U(1) symmetry. When the Kahler manifold exhibits a no-scale-type symmetry, the model predicts n(s) similar or equal to 0.963 and r similar or equal to 0.004. Beyond no-scale SUGRA, n(s) and r depend crucially on the coefficient involved in the fourth order term, which mixes the inflaton with the accompanying non-inflaton field in the Kahler potential, and the prefactor encountered in it. Increasing slightly the latter above (-3), an efficient enhancement of the resulting r can be achieved putting it in the observable range. The inflaton mass in the last case is confined in the range (5 – 9) . 10(13) GeV.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2015). Search for a Charged Higgs Boson Produced in the Vector-Boson Fusion Mode with Decay H-+/- -> W(+/-)Z using pp Collisions at root S=8 TeV with the ATLAS Experiment. Phys. Rev. Lett., 114(23), 231801–18pp.
Abstract: A search for a charged Higgs boson, H-+/-, decaying to a W-+/- boson and a Z boson is presented. The search is based on 20.3 fb(-1) of proton-proton collision data at a center-of-mass energy of 8 TeV recorded with the ATLAS detector at the LHC. The H-+/- boson is assumed to be produced via vector-boson fusion and the decays W-+/- -> q (q') over bar and Z -> e(+)e(-)/mu(+)mu(-) are considered. The search is performed in a range of charged Higgs boson masses from 200 to 1000 GeV. No evidence for the production of an H+ boson is observed. Upper limits of 31-1020 fb at 95% C.L. are placed on the cross section for vector-boson fusion production of an H-+/- boson times its branching fraction to W(+/-)Z. The limits are compared with predictions from the Georgi-Machacek Higgs triplet model.
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