New ambiguity in probing CP violation in neutrino oscillations
(Submitted on 19 Apr 2016)
If neutrinos get mass a la seesaw the mixing matrix describing neutrino oscillations can be effectively non-unitary. We show that in this case the neutrino appearance probabilities involve a new CP phase, phi, associated to non-unitarity. This leads to an ambiguity in extracting the “standard” three–neutrino phase delta_CP, which can survive even after neutrino and antineutrino channels are combined. Its existence should be taken into account in the planning of any oscillation experiment aiming at a robust measurement of delta_CP.
Has a Higgs-flavon with a 750 GeV mass been detected at the LHC13?
(Submitted on 17 Apr 2016)
Higgs-flavon fields appear as part of the Froggart-Nielsen (FN) mechanism, which attempts to explain the hierarchy of Yukawa couplings. We explore the possibility that the 750 GeV diphoton resonance recently reported at the LHC13, could be identified with a low-scale Higgs-flavon field HF. We work within an extension of the standard model (SM) that contains two Higgs doublets (a standard one and an inert one) and one complex FN singlet. The inert doublet includes a stable neutral boson, which provides a viable dark matter candidate, while the mixing of the standard doublet and the FN singlet induces flavor violation in the Higgs sector at the tree-level. Constraints on the parameters of the model are derived from the LHC Higgs data, which include the search for the lepton flavor violating decay of the SM Higgs boson h→μ¯τ. We also identify the viable parameter space that can reproduce the profile of the 750 GeV diphoton signal; in particular, the heavy fermions from the ultraviolet completion of the FN mechanism must play an important role to reproduce the large width of the signal. In addition, we find that the model predicts a large branching ratio for the HF→hh decay, of the order of 0.1, which should be searched for at the LHC13 to test this model.
Landau-Khalatnikov-Fradkin transformations in Reduced Quantum Electrodynamics
(Submitted on 13 Apr 2016)
We derive the Landau-Khalatnikov-Frandkin transformation (LKFT) for the fermion propagator in quantum electrodynamics (QED) described within a brane-world inspired framework where photons are allowed to move in dγ space-time (bulk) dimensions while electrons remain confined to a de-dimensional brane, with de<dγ, referred to in the literature as Reduced Quantum Electrodynamics, RQEDdγ,de. Specializing to the case of graphene, namely RQED4,3 with massless fermions, we derive the non-perturbative form of the fermion propagator starting from its bare counterpart and then compare its weak coupling expansion to known one- and two-loop perturbative results. The agreement of the gauge dependent terms at order α and α2 is reminiscent from the structure of LKFT in ordinary QED in arbitrary space-time dimensions and provides strong constraints for the multiplicative renormalizability of RQEDdγ,de.
Thermal photon production from gluon fusion induced by magnetic fields in relativistic heavy-ion collisions
(Submitted on 10 Apr 2016)
We compute the production of thermal photons in relativistic heavy-ion collisions by gluon fusion in the presence of an intense magnetic field, and during the early stages of the reaction. This photon yield is an excess over calculations that do not consider magnetic field effects. We add this excess to recent hydrodynamic calculations that are close to describing the experimental transverse momentum distribution in RHIC and LHC. We then show that with reasonable values for the temperature, magnetic field strength, and strong coupling constant, our results provide a very good description of such excess. These results support the idea that the origin of at least some of the photon excess observed in heavy-ion experiments may arise from magnetic field induced processes.
Inverse problems for Jacobi operators IV: Interior mass-spring perturbations of semi-infinite systems
(Submitted on 1 Apr 2016)
This work gives results on the interplay of the spectra of two Jacobi operators corresponding to an infinite mass-spring system and a modification of it obtained by changing one mass and one spring of the system. It is shown that the system can be recovered from these two spectra. Necessary and sufficient conditions for two sequences to be the spectra of the mass-spring system and the perturbed one are provided.
H→ℓℓ′ in the Simplest Little Higgs Model
(Submitted on 31 Mar 2016)
Little Higgs Models are promising constructs to solve the hierarchy problem affecting the Higgs boson mass for generic new physics. However, their preservation of lepton universality forbids them to account for the H→τμ CMS hint and at the same time respect (as they do) the severe limits on H→μe inherited from the non-observation of μ→eγ. We compute the predictions of the Simplest Little Higgs Model for the H→ℓℓ′ decays and conclude that the measurement of any of these decays at LHC (even with a much smaller rate than currently hinted) will rule out this model. This result is consistent with our earlier observation of very suppressed lepton flavor violating semileptonic tau decays within this model.
Relating q̂ , η/s and ΔE in an expanding Quark-Gluon Plasma
(Submitted on 30 Mar 2016)
We use linear viscous hydrodynamics to describe the energy and momentum deposited by a fast moving parton in a quark gluon plasma. This energy-momentum is in turn used to compute the probability density for the production of soft partons by means of the Cooper-Frye formula. We use this probability density to render manifest a relation between the average transverse momentum given to the fast moving parton from the medium q̂ , the entropy density to shear viscosity ratio η/s and the energy lost by the fast moving parton ΔE in an expanding medium under similar conditions to those generated in nucleus-nucleus collisions at the LHC. We find that q̂ increases linearly with ΔE for both trigger and away side partons that have been produced throughout the medium. On the other hand, η/s is more stable with ΔE. We also study how these transport coefficients vary with the geometrical location of the hard scattering that produces the fast moving partons. The behavior of q̂ , with ΔE is understood as arising from the length of medium the parton traverses from the point where it is produced. However, since η/s is proportional to the ratio of the length of medium traversed by the fast parton and the average number of scatterings it experiences, it has a milder dependence on the energy it loses. This study represents a tool to obtain a direct connection between transport coefficients and the description of in-medium energy loss within a linear viscous hydrodynamical evolution of the bulk.