arXiv subjects

R. Martinez

Publications and source records attributed to R. Martinez.

At least 73 records · Page 4Linked to original sources

arXiv2012

In-plane Dielectric and Magnetoelectric Studies of BiFeO3

In-plane temperature dependent dielectric behavior of BiFeO3 (BFO) as-grown thin films show diffuse but prominent phase transitions near 450 (+/-10) K and 550 K with dielectric loss temperature dependences that suggest skin layer effects. The 450 K anomalies are near the "transition" first reported by Polomska et al. [Phys. Stat. Sol. 23, 567 (1974)]. The 550 K anomalies coincide with the surface phase transition recently reported [Xavi et al. PRL 106, 236101 (2011)]. In addition, anomalies are found at low temperatures: After several experimental cycles the dielectric loss shows a clear relaxor-like phase transition near what was previously suggested to be a spin reorientation transition (SRT) temperature (~ 201 K) for frequencies 1 kHz < f < 1MHz which follow a nonlinear Vogel-Fulcher (V-F) relation; an additional sharp anomaly is observed near ~180 K at frequencies below 1 kHz. As emphasized recently by Cowley et al. [Adv. Phys. 60, 229 (2011)], skin effects are expected for all relaxor ferroelectrics. Using the interdigital electrodes, experimental data and a theoretical model for in-plane longitudinal and transverse direct magnetoelectric (ME) coefficient are presented.

cond-mat.mtrl-sci↗

arXiv2011

A 3-3-1 model with SU(8) unification

We construct a 3-3-1 model for three families that can be embedded into a single SU(8) unified model. Assuming appropriate branching rules and symmetry-breaking pattern, we find a complete fermion content within irreducible representations of SU(8), where light standard model fermions, heavy 3-3-1 fermions and super-heavy fermions may be distinguished. In the framework of the doubly lopsided mechanism, we obtain mass matrix structures which exhibit nontrivial flavor hierarchical features. Among the up-type quarks, one (top quark) has tree-level mass and two (charm and up) get masses at one-loop level. Considering only dominant contributions, we may obtain the ratios $|m_c/m_t| \approx 7.4 \times 10^{-3}$ and $|m_u/m_c| \approx 1.9 \times 10^{-3}$ with few assumptions on the free parameters and without any hierarchical requirements on the Yukawa couplings.

hep-ph↗

arXiv2010

Adsorption of molecular gases on porous materials in the SAFT-VR approximation

A simple molecular thermodynamic approach is applied to the study of the adsorption of gases of chain molecules on solid surfaces. We use a model based on the Statistical Associating Fluid Theory for Variable Range (SAFT-VR) potentials [A. Gil-Villegas, A. Galindo, P. J. Whitehead, S. J. Mills, G. Jackson, A. N. Burgess, J. Chem. Phys. 106 (1997) 4168] that we extend by including a quasi-two-dimensional approximation to describe the adsorption properties of this type of real gases [A. Martinez, M. Castro, C. McCabe, A. Gil-Villegas, J. Chem. Phys. 126 (2007) 074707]. The model is applied to ethane, ethylene, propane, and carbon dioxide adsorbed on activated carbon and silica gel, which are porous media of significant industrial interest. We show that the adsorption isotherms obtained by means of the present SAFT-VR modeling are in fair agreement with the experimental results provided in the literature

physics.comp-ph↗

arXiv2010

Flavor changing neutral currents in 331 models

We carry out a general analysis of tree level flavor changing neutral currents in the context of 331 models, considering arbitrary quark and gauge boson mixing matrices. The results are applied to definite textures of quark mass matrices, and differences between various 331 scenarios are pointed out.

hep-ph↗

arXiv2009

Heavy quark signals from radiative corrections to the $Z^{\prime}$ boson decay in 3-3-1 models

One-loop corrections to the $Z^{\prime}$ decay width are derived and analyzed in the framework of the general form of the 3-3-1 models. We identify two important sources of corrections: oblique corrections asociated to the $Z^{\prime}$ propagator through vacum polarizations induced by virtual particle-antiparticle pairs of new heavy quarks $J$, and vertex corrections to the $Z^{\prime}q\bar{q}$ vertex through virtual exchange of new $K^{Q_{1,2}}$ gauge bosons. Fixing an specific renormalization scheme, we obtain dominant oblique corrections that exhibit a quadratic dependence on the $J$ quark mass, which are absorbed into two oblique parameters: a global parameter $ρ^{\prime}_f$ which modify the $Z^{\prime}$ decay width, and a parameter $κ^{\prime}_{f}$ that define effective $Z^{\prime}$ couplings. Numerical results in an specific 3-3-1 model gives a strong contribution of the oblique corrections from about 1.3% in the $d(s)$ quark channel to 10.5% in the neutrino channel, for $m_{J}=2$ TeV. The vertex corrections contribute to the oblique corrections up to 1.4% for the same channel and $m_{J}$ value. For $pp$ collisions at the CERN LHC collider, we find that the corrections significantly modify the shape of the cross section distributions for $e^{+}e^{-}$ and $t\bar{t}$ final states, where the distributions including the radiative corrections increases up to 1.23 times the tree-level distribution for the dielectron events and to 1.07 for the top events when $m_{J}=3$ TeV.

hep-ph↗

arXiv2009

Z' boson detection in the Minimal Quiver Standard Model

We undertake a phenomenological study of the extra neutral Z' boson in the Minimal Quiver Standard Model and discuss limits on the model's parameters from previous precision electroweak experiments, as well as detection prospects at the Large Hadron Collider at CERN. We find that masses lower than around 700 GeV are excluded by the $Z$-pole data from the CERN-LEP collider, and below 620 GeV by experimental data from di-electron events at the Fermilab-Tevatron collider. We also find that at a mass of 1 TeV the LHC cross section would show a small peak in the di-lepton and top pair channel.

hep-ph↗

arXiv2009

Unparticle effects in neutrino telescopes

Recently H.Georgi has introduced the concept of unparticles in order to describe the low energy physics of a nontrivial scale invariant sector of an effective theory. We investigate its physical effects on the neutrino flux to be detected in a kilometer cubic neutrino telescope such as IceCube. We study the effects, on different observables, of the survival neutrino flux after through the Earth and the regeneration originated in the neutral currents. We calculate the contribution of unparticle physics to the neutrino-nucleon interaction and, then, to the observables in order to evaluate detectable effects in IceCUbe. Our results are compared with the bounds obtained by other non-underground experiments. Finally, the results are presented as an exclusion plot in the relevant parameters of the new physics stuff.

hep-ph↗

arXiv2008

Light Higgs Boson Production in Two Higgs Doublets Models type III

By using the Cheng, Sher and Yuan's anzats, we study the light Higgs Boson production associated with $b$ quark production at TEVATRON using the 2HDM type III. We compare the simulations with experimental results coming from TEVATRON, finding valid ranges for the $bb$ coupling. By using these results, we calculate the cross section for the process $pp \to b\bar bh(b\bar b)$ for the LHC collider.

hep-ph↗

arXiv2008

Charged Higgs production at photon colliders in 2HDM-III

We study charged Higgs production in the process $γγ\to A^0\to W^- H^+$. The processes $γγ\to A^0$ are loop mediated in a 2HDM. This is due to the fact that photons only couple directly to charged particles and the Higgs only couples to particles with mass acquired via Higgs mechanism. Although in MSSM the contribution from the process $γγ\to A^0$ is too small, it has been found that in a more general 2HDM it could be enhanced. On the other hand, the boson $A^0$ can decay in $W^- H^+$ at tree level and the charged Higgs can decay in fermions. So, the whole process under study is $γγ\to A^0\to (W^-\to lν) (H^+\to f_if_j)$ in 2HDM-III. Evidence about charged Higgs existence could demonstrate that structure of the Higgs sector has several multiplets.

hep-ph↗

arXiv2008

Phenomenological aspects of the exotic $T$ quark in 331 models

In the context of 331 models we analyze the phenomenology of exotic $T$ quarks with electric charge 2/3. We establish bounds for the corresponding masses and mixing angles and study the decay modes $T\to bW$, $tZ$ and $qH$. It is found that the decays into scalars are strongly dependent on the model parameters, and can be the dominant ones in a scenario with approximate flavor symmetry.

hep-ph↗

arXiv2008

Constraints on unparticle physics from the $gt\bar t$ anomalous coupling

We study the impact of unparticle physics to the chromomagnetic dipole moment (CMDM) of the top quark. We compute the effect induced by unparticle operators of scalar and vector nature coupled to fermions on the CMDM. We find that this dipole moment is sensitive to the scale dimensions $d_u$ of the unparticle and the new couplings of the respective effective operators. Using the bounds imposed on the CMDM by low-energy precision and Tevatron measurements we derive indirect limits on the unparticle parameter space. In particular, we find that the scalar-unparticle operator contribution fulfills both constraints for most of the unparticle parameter space, while the low-energy precision bound on the CMDM excludes a vector-unparticle contribution for low values of respective scale dimension $d_u$.

hep-ph↗

arXiv2008

$Z^{\prime}$ boson signal at Tevatron and LHC in a 331 model

We analyse the possibilities to detect a new $Z^{\prime}$ boson in di-electron events at Tevatron and LHC in the framework of the 331 model with right-handed neutrinos. Using $p\bar{p}$ collision data collected by the CDF II detector at Fermilab Tevatron, we find that the 331 $Z^{\prime}$ boson is excluded with masses below 920 GeV. For an integrated luminosity of $100 fb^{-1}$ at LHC, and considering a central value $M_{Z^{\prime}}=1500$ GeV, we obtain the invariant mass distribution in the process $pp\to Z^{\prime}\to e^{+}e^{-}$, where a huge peak, corresponding to 800 signal events, is found above the SM background. The number of di-electron events vary from 10000 to 1 in the mass range of $M_{Z^{\prime}}=1000-5000$ GeV.

hep-ph↗

arXiv2008

Mass-matrix ansatz and constraints on $B_{s}^{0}-\bar{B}_{s}^{0}$ mixing in 331 models

Comparing the theoretically predicted and measured values of the mass difference of the $B^{0}_{s}$ system, we estimate the lower bound on the mass of the $Z^{\prime}$ boson of models based on the $SU(3)_{c} \otimes SU(3)_{L} \otimes U(1)_X$ gauge group. By assuming zero-texture approaches of the quark mass matrices, we find the ratio of the measured value to the theoretical prediction from the Standard Model and the $Z^{\prime}$ contribution from the 331 models of the mass difference of the $B^{0}_{s}$ system. We find lower bounds on the $Z^{\prime}$ mass ranging between 1 TeV and 30 TeV for the two most popular 331 models, and four different zero-textures ansätze. The above results are expressed as a function of the weak angle associated to the $b-s-Z^{\prime}$ couplings.

hep-ph↗

arXiv2008

Constraints on economical 331 models from mixing of K, Bd and Bs neutral mesons

We analyze the effect of flavor changing neutral currents within 331 models. In particular, we concentrate in the so-called "economical" models, which have a minimal scalar sector. Taking into account the experimental measurements of observables related to neutral K and B meson mixing, we study the resulting bounds for angles and phases in the mixing matrix for the down quark sector, and the mass and mixing parameters related to the new Z' gauge boson.

hep-ph↗

arXiv2007

FCNC Top Quark Decays in Extra Dimensions

The flavor changing neutral top quark decay t -> c X is computed, where X is a neutral standard model particle, in a extended model with a single extra dimension. The cases for the photon, X= γ$, and a Standard Model Higgs boson, X = H, are analyzed in detail in a non-linear$R_ξgauge. We find that the branching ratios can be enhanced by the dynamics originated in the extra dimension. In the limit where 1/R >> ->, we have found Br(t -> c γ) \simeq 10^{-10} for 1/R = 0.5 TeV. For the decay t -> c H, we have found Br(t -> cH) \simeq 10^{-10} for a low Higgs mass value. The branching ratios go to zero when 1/R -> \infty.

hep-ph↗

arXiv2007

Renormalization Group and Grand Unification with 331 Models

By making a renormalization group analysis we explore the possibility of having a 331 model as the only intermediate gauge group between the standard model and the scale of unification of the three coupling constants. We shall assume that there is no necessarily a group of grand unification at the scale of convergence of the couplings. With this scenario, different 331 models and their corresponding supersymmetric versions are considered, and we find the versions that allow the symmetry breaking described above. Besides, the allowed interval for the 331 symmetry breaking scale, and the behavior of the running coupling constants are obtained. It worths saying that some of the supersymmetric scenarios could be natural frameworks for split supersymmetry. Finally, we look for possible 331 models with a simple group at the grand unification scale, that could fit the symmetry breaking scheme described above.

hep-ph↗

arXiv2007

Different kind of textures of Yukawa coupling matrices in the two Higgs doublet model type III

The quark mass matrices ansatze proposed by Fritzsch, Du-Xing and Fukuyama-Nishiura in the framework of the general two Higgs doublet model are studied. The corresponding Yukawa matrices in the flavor basis in the different cases considered are discussed. The corresponding Cabbibo-Kobayashi-Maskawa matrix elements are computed in all cases and compared with their experimental values. The complex phases of the ansatze are taken into account and the CP violating phase $δ$ is computed. Finally, in order to observe the influence of the different kind of textures of Yukawa coupling matrices considered, some phenomenology of two body decays of the top quark, the lightest Higgs boson and the charged Higgs boson is discussed.

hep-ph↗

arXiv2006

Experimental Implementation of Logical Bell State Encoding

Liquid phase NMR is a general purpose test-bed for developing methods of coherent control relevant to quantum information processing. Here we extend these studies to the coherent control of logical qubits and in particular to the unitary gates necessary to create entanglement between logical qubits. We report an experimental implementation of a conditional logical gate between two logical qubits that are each in decoherence free subspaces that protect the quantum information from fully correlated dephasing.

quant-ph↗