arXiv subjects

Claudio O. Dib

Publications and source records attributed to Claudio O. Dib.

30 records · Page 2Linked to original sources

arXiv2014

Neutrinos with a linear seesaw mechanism in a scenario of gauged B-L symmetry

We consider a mechanism for neutrino mass generation, based on a local B-L extension of the standard model, which becomes a linear seesaw regime for light neutrinos after spontaneous symmetry breaking. The spectrum of extra particles includes heavy neutrinos with masses near the TeV scale and a heavy Z' boson, as well as three extra neutral scalars and a charged scalar pair. We study the production and decays of these heavy particles at the LHC. Z' will decay mainly into heavy neutrino pairs or charged lepton pairs, similar to other low scale seesaw scenarios with local B-L, while the phenomenology of the extra scalars is what distinguishes the linear seesaw from the previous models. One of the neutral scalars is produced by Z' Z' fusion and decays mainly into vector boson pairs, the other two neutral scalars are less visible as they decay only into heavy or light neutrino pairs, and finally the charged scalars will decay mainly into charged leptons and missing energy.

hep-ph↗

arXiv2014

The Effect of Composite Resonances on Higgs decay into two photons

In scenarios of strongly coupled electroweak symmetry breaking, heavy composite particles of different spin and parity may arise and cause observable effects on signals that appear at loop levels. The recently observed process of Higgs to $γγ$ at the LHC is one of such signals. We study the new constraints that are imposed on composite models from $H\to γγ$, together with the existing constraints from the high precision electroweak tests. We use an effective chiral Lagrangian to describe the effective theory that contains the Standard Model spectrum and the extra composites below the electroweak scale. Considering the effective theory cutoff at $Λ= 4πv \sim 3 $ TeV, consistency with the $T$ and $S$ parameters and the newly observed $H\to γγ$ can be found for a rather restricted range of masses of vector and axial-vector composites from $1.5$ TeV to $1.7$ TeV and $1.8$ TeV to $1.9$ TeV, respectively, and only provided a non-standard kinetic mixing between the $W^{3}$ and $B^{0}$ fields is included.

hep-ph↗

arXiv2014

Remarks on the lifetime of sterile neutrinos and the effect on detection of rare meson decays M+ -> M'- lepton+ lepton+

We review the detection of the Delta L=2 semileptonic meson decays of the form M(+) -> M'(-) lepton(+) lepton(-) that we studied in a previous work, mediated by a Majorana neutrino with a mass in the range between the masses of the initial and final mesons. For such range of masses, the Majorana neutrino will go on its mass shell and the two charged leptons will appear at displaced vertices or, if the lifetime is long enough, most secondary vertices will fall outside the detector. We study the consequences of this effect on the experimental searches and limits that can be extracted.

hep-ph↗

arXiv2012

Chi_b(3P) splitting predictions in potential models

Recently a new state of the b - anti b system has been observed by the ATLAS Collaboration, with a mass of 10530 +/- 5 +/- 9 MeV. This state has been identified with the n=3 P-wave radial excitations of the b - anti b system with parallel quark spins, called chi_b(3P). The measured value of the mass corresponds to the average of the J=0, 1 and 2 states, while the splittings of these states are not yet resolved. In this work we present predictions from different potentials models for the values of these splittings.

hep-ph↗

arXiv2012

Quark masses and mixings in the RS1 model with a condensing 4th generation

We study the hierarchy of quark masses and mixings in a model based on a 5-dimensional spacetime with constant curvature of Randall-Sundrum type with two branes, where the Electroweak Symmetry Breaking is caused dynamically by the condensation of a 4th generation of quarks, due to underlying physics from the 5D bulk and the first KK gluons. We first study the hierarchy of quark masses and mixings that can be obtained from purely adjusting the profile localizations, finding that realistic masses are not reproduced unless non trivial hierarchies of underlying 4-fermion interactions from the bulk are included. Then we study global U(1) symmetries that can be imposed in order to obtain non-symmetric modified Fritzsch-like textures in the mass matrices that reproduce reasonably well quark masses and CKM mixings.

hep-ph↗

arXiv2010

Spin-down of neutron stars by neutrino emission

We study the spin-down of a neutron star during its early stages due to the neutrino emission. The mechanism we consider is the subsequent collisions of the produced neutrinos with the outer shells of the star. We find that this mechanism can indeed slow down the star rotation but only in the first tens of seconds of the core formation, which is when the appropriate conditions of flux and collision rate are met. We find that this mechanism can extract less than 1 % of the star angular momentum, a result which is much less than previously estimated by other authors.

astro-ph.HE↗

arXiv2008

A new signature for color octet pseudoscalars at the LHC

Color octet (pseudo)scalars, if they exist, will be copiously produced at the CERN Large Hadron Collider (LHC). However, their detection can become a very challenging task. In particular, if their decay into a pair of top quarks is kinematically forbidden, the main decay channel would be into two jets, with a very large background. In this Brief Report we explore the possibility of using anomaly-induced decays of the color octet pseudoscalars into gauge bosons to find them at the LHC.

hep-ph↗

arXiv2006

Lepton flavor violation in muonium decay and muon colliders in models with heavy neutrinos

We study the lepton-flavor-violating reaction $μ^+ e^- \to e^+ e^-$ within two extensions of the standard model that include heavy neutrinos. The reaction is studied in the low energy limit in the form of muonium decay $M\to e^+ e^-$ and in the high energy regime of a muon collider. The two theoretical models we consider are: model I, a typical see-saw model that violates lepton flavor and number by inclusion of extra right handed neutrinos, and model II, a variant where lepton number is conserved and which includes extra right handed as well as left handed neutrinos, singlets under the gauge group. We find for muonium decay into $e^+e^-$ the extremely small result $Br(M\to e^+ e^-) < 10^{-19}$ in both scenarios. Alternatively, for $μ^+ e^-$ collisions up to $\sqrt{s}\sim 50$ GeV we find $σ(μ^+ e^- \to e^+ e^-)< 10^{-5}$ fb, while for energies above the $W^+ W^-$ threshold we find $σ(μ^+ e^- \to W^+ W^-)$ up to 1 fb.

hep-ph↗

arXiv2005

Double Higgs Production and Quadratic Divergence Cancellation in Little Higgs Models with T Parity

We analyze double Higgs boson production at the Large Hadron Collider in the context of Little Higgs models. In double Higgs production, the diagrams involved are directly related to those that cause the cancellation of the quadratic divergence of the Higgs self-energy, providing a robust prediction for this class of models. We find that in extensions of this model with the inclusion of a so-called T-parity, there is a significant enhancement in the cross sections as compared to the Standard Model.

hep-ph↗

arXiv2005

Double Higgs Production at the LHC as a robust test of Little Higgs models

We analyze double Higgs boson production at the LHC in the context of Little Higgs models. In double Higgs production, the diagrams involved are directly related to those that cause the cancellation of the quadratic divergence of the Higgs self-energy, so this mode provides a robust prediction for this class of models. We find that in extensions of this model with the inclusion of a so-called T-parity, there is a significant enhancement in the cross sections as compared to the Standard Model.

hep-ph↗

arXiv2005

Muonium-antimuonium conversion in models with heavy neutrinos

We study muonium-antimuonium conversion and mu+ e- to mu- e+ scattering within two different lepton-flavor-violating models with heavy neutrinos: model I is a typical seesaw that violates lepton number as well as flavor; model II has a neutrino mass texture where lepton number is conserved. We look for the largest possible amplitudes of these processes that are consistent with current bounds. We find that model I has very limited chance of providing an observable signal, except if a finely tuned condition in parameter space occurs. Model II, on the other hand, requires no fine tuning and could cause larger effects. However, the maximum amplitude provided by this model is still two orders of magnitude below the sensitivity of current experiments: one predicts an effective coupling G_MM up to 10^{-4}G_F for heavy neutrino masses near 10 TeV. We have also clarified some discrepancies in previous literature on this subject.

hep-ph↗

arXiv2001

The Magnetized Electron Gas in terms of Hurwitz Zeta Functions

We obtain explicit expressions for thermodynamic quantities of a relativistic degenerate free electron gas in a magnetic field in terms of Hurwitz Zeta functions. The formulation allows for systematic expansion in all regimes. Three energy scales appear naturally in the degenerate relativistic gas: the Fermi energy Ef, the temperature T and an energy related to the magnetic field or Landau level spacing, eB/Ef. We study the cold and warm scenarios, T << eB/Ef and eB/Ef << T, respectively. We reproduce the oscillations of the magnetization as a function of the field in the cold regime and the dilution of them in the warm regime.

math-ph↗