arXiv subjects

Rodolfo A. Diaz

Publications and source records attributed to Rodolfo A. Diaz.

At least 37 records · Page 2Linked to original sources

arXiv2005

On the transformation of torques between the laboratory and center of mass reference frames

It is commonly stated in Newtonian Mechanics that the torque with respect to the laboratory frame is equal to the torque with respect to the center of mass frame plus a (R X F) factor, with "R" being the position of the center of mass and "F" denoting the total external force. Although this assertion is true, there is a subtlety in the demonstration that is overlooked in the textbooks. In addition, it is necessary to clarify that if the reference frame attached to the center of mass rotates with respect to certain inertial frame, the assertion is not true any more.

physics.ed-ph↗

arXiv2005

Improving bounds on flavor changing vertices in the two Higgs doublet model from $B-\bar{B}$ mixing

We find some constraints on the flavor changing vertices of the two Higgs doublet model, from the ΔM_{B_{d}} measurement. Although bounds from this observable have already been considered, this paper takes into account the role of a new operator not included previously, as well as the vertices ξ_{bb}, ξ_{tc} and ξ_{sb}. Using the Cheng-Sher parametrization, we found that for a relatively light charged Higgs boson (200-300 GeV), we get that λ_{tt}<1, while the parameter λ_{bb} could have values up to about 50. In addition, we use bounds for λ_{tt} and λ_{bb} obtained from B^{0}->X_{s}γat next to leading order, and studied the case where the only vanishing vertex factors are the ones involving quarks from the first family. We obtained that ΔM_{B_{d}} is not sensitive to the change of the parameter λ_{sb}, while λ_{tc}<1

hep-ph↗

arXiv2005

Reparameterization of the scalar potential in the two Higgs doublet model

In the two Higgs doublet model with no additional symmetries in the scalar sector (different from the gauge and Lorentz symmetries), it is customary to reparameterize the model by rotating the scalar doublets such that one of the vacuum expectation values vanishes. It is well known that the Yukawa sector of the model is unaffected by such transformation. Notwithstanding, since the Higgs potential must also be transformed, it is necessary to show that such sector is also unaltered in its physical content. We demostrate that the physical content of the potential is invariant even when the charge conjugation symmetry is demanded.

hep-ph↗

arXiv2005

331 vector-like models with mirror fermions as a possible solution for the discrepancy in the b-quark asymmetries, and for the neutrino mass and mixing pattern

A general study of the fermionic structure of the 331 models with βarbitrary shows the possibility of obtaining 331 vector-like models with mirror fermions. On one hand, the existence of mirror fermions gives a possible way to fit the discrepancy in the bottom quark asymmetries from the prediction of the standard model. On the other hand, the vector-like nature of the model permits to address the problem of the fermion mass hierarchy, and in particular the problem of the neutrino mass and mixing pattern. Specifically, we consider a model with four families and β=-1/\sqrt{3} where the additional family corresponds to a mirror fermion of the third generation of the Standard Model. We also show how to generate ansatzs about the mass matrices of the fermions according to the phenomenology. In particular, it is possible to get a natural fit for the neutrino hierarchical masses and mixing angles. Moreover, by means of the mixing between the third quark family and its mirror fermion, a possible solution for the A_{FB}^{b} discrepancy is obtained.

hep-ph↗

arXiv2005

SU(3)_{c} X SU(3)_{L} X U(1)_{X} models for βarbitrary and families with mirror fermions

A detailed and general study of the fermionic structure of the 331 models with βarbitrary is carried out based on the criterion of cancellation of anomalies. We consider models with an arbitrary number of lepton and quark generations, but requiring to associate only one lepton and one quark SU(3) _{L} multiplet for each generation, and at most one right-handed singlet per each left-handed fermion. We see that the number of quark left-handed multiplets must be three times the number of leptonic left-handed multiplets. Furthermore, we consider a model with four families and β=-1/\sqrt{3} where the additional family corresponds to a mirror fermion of the third generation of the Standard Model. We also show how to generate ansatzs about the mass matrices of the fermions according to the phenomenology. In particular, it is possible to get a natural fit for the neutrino hierarchical masses and mixing angles. Moreover, by means of the mixing between the third quark family and its mirror fermion, a possible solution for the A_{FB}^{b} discrepancy is obtained.

hep-ph↗

arXiv2005

Using symmetries and generating functions to calculate and minimize moments of inertia

This paper presents some formulae to calculate moments of inertia for solids of revolution and for solids generated by contour plots. For this, the symmetry properties and the generating functions of the figures are utilized. The combined use of generating functions and symmetry properties greatly simplifies many practical calculations. In addition, the explicit use of generating functions gives the possibility of writing the moment of inertia as a functional, which in turn allows to utilize the calculus of variations to obtain a new insight about some properties of this fundamental quantity. In particular, minimization of moments of inertia under certain restrictions is possible by using variational methods.

physics.class-ph↗

arXiv2005

Higgs boson decay in the large N limit

The Equivalence Theorem is commonly used to calculate perturbatively amplitudes involving gauge bosons at energy scales higher than gauge boson masses. However, when the scalar sector is strongly interacting the theory is non-perturbative. We show that the Equivalence Theorem holds in the large N limit at next-to-leading order by calculating the decay widths h -> W^{+}W^{-} and h->π^{+}π^{-}. We also show, in the same scheme of calculations, that unitarity is fulfilled for the process h->π^{+}π^{-}.

hep-ph↗

arXiv2004

Flavor changing neutral currents from lepton and B decays in the two Higgs doublet model

Constraints on the whole spectrum of lepton flavor violating vertices are shown in the context of the standard two Higgs doublet model. The vertex involving the $e-τ$ mixing is much more constrained than the others, and the decays proportional to such vertex are usually very supressed. On the other hand, bounds on the quark sector are obtained from leptonic decays of the $B_{d,s}^{0}$ mesons and from $ΔM_{B_{d}^{0}}$. We emphasize that although the $B_{d}^{0}-\bar{B}_{d}^{0}$ mixing restricts severely the $% d-b$ mixing vertex, the upper bound for this vertex could still give a sizeable contribution to the decay $B_{d}^{0}\to μ\barμ$ respect to the standard model contribution, from which we see that such vertex could still play a role in the phenomenology.

hep-ph↗

arXiv2004

The scalar sector of the $SU(3)_{c}\otimes SU(3)_{L}\otimes U(1)_{X}$ model

A complete study of the Higgs sector of the $SU(3)_{c}\otimes SU(3)_{L}\otimes U(1)_{X}$ model is carried out, obtaining all possible cases of vacuum expectation values that permit the spontaneous symmetry breaking pattern$ SU(3)_{L}\otimes U(1)_{X}\to SU(2)_{L}\otimes U(1)_{Y}\to U(1)_{Q}.$ We find the most general Higgs potentials that contain three triplets of Higgs and one sextet. A detailed study of the scalar sector for different models with three Higgs triplets is done. The models end up in an electroweak two Higgs doublet model after the first symmetry breakdown; we find that the low energy limit depends on a trilinear parameter of the Higgs potential, and that the decoupling limit from the electroweak two Higgs doublet model to the minimal standard model can be obtained quite naturally.

hep-ph↗

arXiv2003

Constraints on lepton flavor violation in the two Higgs doublet model

hep-ph↗

arXiv2003

Comparative kinetics of the snowball respect to other dynamical objects

We examine the kinetics of a snowball that is gaining mass while is rolling downhill. This dynamical system combines rotational effects with effects involving the variation of mass. In order to understand the consequences of both effects we compare its behavior with the one of some objects in which such effects are absent. Environmental conditions are also included. We conclude that the comparative velocity of the snowball is very sensitive to the hill profile and the retardation factors. We emphasize that the increase of mass (inertia), could surprisingly diminish the retardation effect due to the drag force. Additionally, when an exponential trajectory is assumed, the maximum velocity of the snowball can be reached at an intermediate step of the trip.

physics.class-ph↗

arXiv2003

Phenomenological analysis of the Two Higgs Doublet Model

The Two Higgs Doublet model and its phenomenological implications are discussed. A brief survey on the present status of this model is given. In particular, we concentrate on the Two Higgs Doublet Model with Flavor Changing Neutral Currents. First, we develop some new parametrizations of the 2HDM type III, in such a way that the relation of it with models type I and type II become apparent. Based on this parametrization we get some bounds on the mixing vertex involving the second and third lepton generations, and lower bounds on the mass of the pseudoscalar Higgs boson. Further, by using a parametrization in which one of the vacuum expectation values vanishes, we constrain some lepton flavor violating vertices, based on the $g-2 $muon factor and some lepton flavor violating decays. Moreover, upper limits on the decay widths of $τ\to eγ, $and $τ\to eee $are calculated, finding them to stay far from the reach of near future experiments. On the other hand, as an addendum to this work, we study the production and decays of top squarks at the Tevatron collider in models of low-energy supersymmetry breaking. We consider that the lightest Standard Model superpartner is a light neutralino that predominantly decays into a photon and a light gravitino, and that the lighter stop is the next-to-lightest Standard Model superpartner. For a modest projection of the final Tevatron luminosity, $L\simeq 4$ fb$^{-1}$, stop masses of order 300 GeV are accessible. We also consider the production and decay of ten degenerate squarks, and we find that common squark masses up to 360 GeV are easily accessible, and that the reach increases further if the gluino is light.

hep-ph↗

arXiv2003

The custodial symmetry

In the present work, we elucidate the meaning of the custodial symmetry and its importance at the phenomenological level in the framework of the standard model of the electroweak interactions and its possible extensions.

hep-ph↗

arXiv2003

Excited tau lepton contribution to $W->tau nu(tau)$ decay at the one-loop level

We evaluate the compositeness effects of tau lepton on the vertex W-tau-nu(tau) in the context of an effective Lagrangian approach. We consider that only the third family is composed and we get the corrections to the non universal lepton coupling g_(tau)/g_(e). As the experimental bounds on non universal lepton couplings in W decays are weak, we find that the excited particles contributions do not give realistic limits on the excited mass, since they lead to Lambda<m*.

hep-ph↗

arXiv2002

Phenomenology of lepton flavor violation in 2HDM(III) from (g-2)_mu and leptonic decays

We constrain some lepton flavor violating vertices in the context of the two Higgs doublet model type III, assuming that the lightest scalar Higgs mass $% m_{h^{0}} $is about $115 $GeV. Specifically, based on the $g-2 $muon factor and the decay width of$ μ\to eγ$,$ $the following quite general bounds are obtained:$ 7.62\times 10^{-4}\lesssim ξ_{μτ}^{2}\lesssim 4.44\times 10^{-2}, $ $ξ_{eτ}^{2}\lesssim 2.77\times 10^{-14}$. Additionally, based on the processes $τ\to μγ$, and $τ\to μμμ$, bounds on $ξ_{ττ} $and $ξ_{μμ} $are also gotten, such constraints on these parameters$ $still give enough room for either a strong suppression$ $or strong enhancement on the coupling of any Higgs boson to a pair of tau leptons or a pair of muons\textbf{.} Furthermore, upper limits on the decay widths of the leptonic decays $τ\to eγ, $and $τ\to eee $are calculated, finding them to stay far from the reach of near future experiments.

hep-ph↗

arXiv2002

The process $μ\to ν_{e}e\barν_μ $in the 2HDM with flavor changing neutral currents

We consider the process $μ\to ν_{e}e\barν_μ $in the framework of a two Higgs doublet model with flavor changing neutral currents (FCNC). Since FCNC generates in turn flavor changing charged currents in the lepton sector, this process appears at tree level mediated by a charged Higgs boson exchange. From the experimental upper limit for this decay, we obtain the bound $| ξ_{μe}/m_{H^{\pm}}| \leq 3.8\times 10^{-3}$ where$ ξ_{μe} $refers to the mixing between the first and second lepton generations, and $m_{H^{\pm}} $denotes the mass of the charged Higgs boson. This bound is independent on the other free parameters of the model. In particular, for $m_{H^{\pm}}\simeq 100$GeV we get $| ξ_{eμ}| $ $\lesssim 0.38$

hep-ph↗

arXiv2002

A new Supersymmetric SU(3)_L otimes U(1)_X gauge model

We present a new supersymmetric version of the SU(3) otimes U(1) gauge model using a more economic content of particles. The model has a smaller set of free parameters than other possibilities considered before. The MSSM can be seen as an effective theory of this larger symmetry. We find that the upper bound of the ligthest CP-even Higgs boson can be moved up to 140 GeV.

hep-ph↗

arXiv2002

Top-squark searches at the Tevatron in models of low-energy supersymmetry breaking

We study the production and decays of top squarks (stops) at the Tevatron collider in models of low-energy supersymmetry breaking. We consider the case where the lightest Standard Model (SM) superpartner is a light neutralino that predominantly decays into a photon and a light gravitino. Considering the lighter stop to be the next-to-lightest Standard Model superpartner, we analyze stop signatures associated with jets, photons and missing energy, which lead to signals naturally larger than the associated SM backgrounds. We consider both 2-body and 3-body decays of the top squarks and show that the reach of the Tevatron can be significantly larger than that expected within either the standard supergravity models or models of low-energy supersymmetry breaking in which the stop is the lightest SM superpartner. For a modest projection of the final Tevatron luminosity, L = 4 fb-1, stop masses of order 300 GeV are accessible at the Tevatron collider in both 2-body and 3-body decay modes. We also consider the production and decay of ten degenerate squarks that are the supersymmetric partners of the five light quarks. In this case we find that common squark masses up to 360 GeV are easily accessible at the Tevatron collider, and that the reach increases further if the gluino is light.

hep-ph↗