arXiv subjects

Marco A. Diaz

Publications and source records attributed to Marco A. Diaz.

At least 19 recordsLinked to original sources

arXiv2015

Confronting recent AMS-02 positron fraction and Fermi-LAT Extragalactic Gamma-Ray Background measurements with gravitino dark matter

Recent positron flux fraction measurements in cosmic-rays (CR) made by the AMS-02 satellite confirm and extends the evidence on the existence of a new (yet unknown) source of high energy positrons. To explain this excess, we use the gravitino of bilinear R-parity violating SUSY models as a decaying Dark Matter candidate, as the source of those high energy particles. Being a long lived weak-interacting and spin 3/2 particle, it offers several particularities which makes it an attractive candidate. We compute the electron, positron and $γ$-ray\ fluxes produced by each gravitino decay channel at the Earth. Combining the flux from the different decay modes we can fit AMS-02 measurements of the positron fraction, as well as the electron and positron fluxes, with a gravitino mass in the range $1-2$ TeV and lifetimes of $\sim 1.0-0.8\times 10^{26}$ s. . Then, we study the viability of these scenarios through their implications in $γ$-ray observations. We set limits on the gravitino lifetime using the Extragalactic $γ$-ray Background recently reported by the {\it Fermi}-LAT Collaboration and a state-of-the-art model of its known contributors. These limits exclude the gravitino parameter space which provides an acceptable explanation of the AMS-02 data. Therefore, we conclude that the gravitino of bilinear R-parity violating models is ruled out as the unique primary source of electrons and positrons needed to explain the rise in the positron fraction.

hep-ph↗

arXiv2014

On Neutrino Masses in the MSSM with BRpV

One loop corrections to the neutrino mass matrix within the MSSM with Bilinear R Parity Violation are calculated, paying attention to the approach in which an effective $3\times 3$ neutrino mass matrix is used. The full mass matrix is block diagonalized, it is found that second and third order terms can be numerically important, and this is analytically understood. Top-stop loops do not contribute to the effective $3\times 3$ at first order, nevertheless they contribute at third. An improved $3\times 3$ approach that include these effects is proposed.

hep-ph↗

arXiv2010

Position resolution and efficiency measurements with large scale Thin Gap Chambers for the super LHC

New developments in Thin Gap Chambers (TGC) detectors to provide fast trigger and high precision muon tracking under sLHC conditions are presented. The modified detectors are shown to stand a high total irradiation dose equivalent to 6 Coulomb/cm of wire, without showing any deterioration in their performance. Two large (1.2 x 0.8 m^2) prototypes containing four gaps, each gap providing pad, strips and wires readout, with a total thickness of 50 mm, have been constructed. Their local spatial resolution has been measured in a 100 GeV/c muon test beam at CERN. At perpendicular incidence angle, single gap position resolution better than 60 microns has been obtained. For incidence angle of 20 degrees resolution of less than 100 micron was achieved. TGC prototypes were also tested under a flux of 10^5 Hz/cm^2 of 5.5-6.5 MeV neutrons, showing a high efficiency for cosmic muons detection.

physics.ins-det↗

arXiv2009

NLO Polarized Chargino pair Production in Electron Positron Annihilation

We calculate the complete one-loop quantum corrections to the helicity eigenstate chargino pair production cross sections in polarized electron positron collisions, within the Minimal Supersymmetric Standard Model. We calculate the non-QED corrections using the helicity amplitudes formalism, and Dimensional Regularization to deal with ultraviolet divergences. We calculate QED corrections using the dipole subtraction formalism to extract soft and collinear divergences in Bremsstrahlung, canceling them with the infrared divergences from virtual QED corrections. We show numerical results for the Focus Point scenario in mSUGRA, where we find important quantum corrections for differential cross sections with definite chargino helicities.

hep-ph↗

arXiv2007

Effect of Charged Scalar Loops on Photonic Decays of a Fermiophobic Higgs

Higgs bosons with very suppressed couplings to fermions ("Fermiophobic Higgs bosons", h_f) can decay to two photons (γγ) with a branching ratio significantly larger than that expected for the Standard Model Higgs boson for m_{h_f}<150 GeV. Such a particle would give a clear signal at the LHC and can arise in the Two Higgs Doublet Model (type I) in which h_f -> γγis mediated by W^+ and charged Higgs boson (H^+) loops. We show that the H^+ loops can cause both constructive and destructive contributions with a magnitude considerably larger than the anticipated precision in the measurement of the photonic decay channel at future hadron and lepton colliders.

hep-ph↗

arXiv2004

Study of a Neutrino Mass Texture Generated in Supergravity with Bilinear R-Parity Violation

We study a particular texture of the neutrino mass matrix generated in supergravity with bilinear R-Parity violation. The relatively high value of $\tanβ$ makes the one-loop contribution to the neutrino mass matrix as important as the tree-level one. The atmospheric angle is nearly maximal, and its deviation from maximal mixing is related to the smallness of the ratio between the solar and atmospheric mass scales. There is also a common origin for the small values of the solar and reactor angles, but the later is much smaller due the large mass ratio between the lightest two neutrinos. There is a high dependence of the neutrino mass differences on the scalar mass $m_0$ and the gaugino mass $M_{1/2}$, but a smaller one of the mixing angles on the same sugra parameters. Measurements of branching ratios for the neutralino decays can give important information on the parameters of the model. There are good prospects at a future Linear Collider for these measurements, but a more detailed analysis is necessary for the LHC.

hep-ph↗

arXiv2004

Double fermiophobic Higgs boson production at the LHC and LC

We consider the phenomenology of a fermiophobic Higgs boson (h_f) at the Large Hadron Collider (LHC) and a e+e- Linear Collider (LC). At both machines the standard production mechanisms which rely on the coupling h_fVV (V=W,Z) can be very suppressed at large tan beta. In such cases the complementary channels pp to H^\pm h_f, A^0 h_f and e+e- to A^0 h_f offer promising cross-sections. Together with the potentially large branching ratios for H^\pm to h_fW* and A^0 to h_fZ*, these mechanisms would give rise to double h_f production, leading to signatures of gamma gamma gamma gamma, gamma gamma VV and VVVV.

hep-ph↗

arXiv2003

On the Large Higher Order Corrections to Polarised Chargino Production

We calculate the radiative corrections to helicity amplitudes for chargino production in electron-positron collisions. We include all weak self-energy, triangle, and box diagrams, and find that the three are important and should be included. We present results in the form of differential cross-sections for four supersymmetry benchmark models, and find usually large corrections and in some cases huge corrections. We conclude that in order to extract the underlying parameters of the chargino sector from collider data taken at a future Linear Collider, a complete theoretical one--loop production cross-section should be used.

hep-ph↗

arXiv2003

Searching for a light Fermiophobic Higgs Boson at the Tevatron

We propose new production mechanisms for light fermiophobic Higgs bosons ($h_f$) with suppressed couplings to vector bosons ($V$) at the Fermilab Tevatron. These mechanisms (e.g. $qq'\to H^\pm h_f$) are complementary to the conventional process $qq'\to Vh_f$, which suffers from a strong suppression of $1/\tan^2β$ in realistic models with a $h_f$. The new mechanisms extend the coverage at the Tevatron Run II to the larger $\tanβ$ region, and offer the possibility of observing new event topologies with up to 4 photons.

hep-ph↗

arXiv2002

Neutrino Physics from Charged Higgs and Slepton Associated Production in AMSB

In the Minimal Supersymmetric Standard Model with bilinear R-Parity violation, terms that violate R-Parity and lepton number are introduced in the superpotential, and sneutrino vacuum expectation values are induced. As a result, neutrino masses and mixing angles are generated via a low energy see-saw mechanism. We show that this model embedded into an anomaly mediated supersymmetry breaking scenario is testable at a linear collider using charged Higgs boson production in association with a stau. This is possible in regions of parameter space where the charged Higgs and stau have similar mass, producing an enhancement of the charged scalar mixing angles. We show that the bilinear parameter and the sneutrino vev can be determined from charged scalar observables, and estimate the precision of this determination.

hep-ph↗

arXiv2000

Radiative Corrections to Chargino Production with Polarized Beams

We show that radiative corrections to chargino production in electron-positron annihilation with polarized beams can be large especially in the case of right handed electrons. In addition, there is some dependency on the squark masses that allows us to extract information about the squark spectrum from the chargino production.

hep-ph↗

arXiv2000

Yukawa Unified Supersymmetric SO(10) Model: Cosmology, Rare Decays and Collider Searches

It has recently been pointed out that viable sparticle mass spectra can be generated in Yukawa unified SO(10) supersymmetric grand unified models consistent with radiative breaking of electroweak symmetry. Model solutions are obtained only if $\tanβ\sim 50$, $μ<0$ and positive $D$-term contributions to scalar masses from SO(10) gauge symmetry breaking are used. In this paper, we attempt to systematize the parameter space regions where solutions are obtained. We go on to calculate the relic density of neutralinos as a function of parameter space. No regions of the parameter space explored were actually cosmologically excluded, and very reasonable relic densities were found in much of parameter space. Direct neutralino detection rates could exceed 1 event/kg/day for a $^{73}$Ge detector, for low values of GUT scale gaugino mass $m_{1/2}$. We also calculate the branching fraction for $b\to s γ$ decays, and find that it is beyond the 95% CL experimental limits in much, but not all, of the parameter space regions explored. However, recent claims have been made that NLO effects can reverse the signs of certain amplitudes in the $b\to sγ$ calculation, leading to agreement between theory and experiment in Yukawa unified SUSY models. For the Fermilab Tevatron collider, significant regions of parameter space can be explored via $b\bar{b}A$ and $b\bar{b}H$ searches. There also exist some limited regions of parameter space where a trilepton signal can be seen at TeV33. Finally, there exist significant regions of parameter space where direct detection of bottom squark pair production can be made, especially for large negative values of the GUT parameter $A_0$.

hep-ph↗

arXiv2000

Two-Body Decays of the Lightest Stop in Supergravity with and without R-Parity

We study the decays of the lightest top squark in supergravity models with and without R-parity. Using the simplest model with an effective explicit bilinear breaking of R-parity and radiative electroweak symmetry breaking we show that, below the threshold for decays into charginos $\tilde t_1\to cχ^+_1$, the lightest stop decays mainly into third generation fermions, $\tilde t_1\to bτ$ instead of the R-parity conserving mode $\tilde t_1\to cχ^0_1$, even for tiny tau--neutrino mass values. Moreover we show that, even above the threshold for decays into charginos, the decay $\tilde t_1\to bτ$ may be dominant. We study the role played by the universality of the boundary conditions on the soft supersymmetry breaking terms. This new decay mode $\tilde t_1\to bτ$ as well as the cascades originated by the conventional $\tilde t_1\to cχ^0_1$ decay followed by the R-parity violating neutralino decays can provide new signatures for stop production at LEP and the Tevatron.

hep-ph↗

arXiv2000

Sparticle Mass Spectra from SO(10) Grand Unified Models with Yukawa Coupling Unification

We examine the spectrum of superparticles obtained from the minimal SO(10) grand unified model, where it is assumed the gauge symmetry breaking yields the Minimal Supersymmetric Standard Model (MSSM) as the effective theory at $M_{GUT}\sim 2\times 10^{16}$ GeV. In this model, unification of Yukawa couplings implies a value of $\tanβ\sim 45-55$. At such high values of $\tanβ$, assuming universality of scalar masses, the usual mechanism of radiative electroweak symmetry breaking breaks down. We show that a set of weak scale sparticle masses consistent with radiative electroweak symmetry breaking can be generated by imposing non-universal GUT scale scalar masses consistent with universality within SO(10) plus extra $D$-term contributions associated with the reduction in rank of the gauge symmetry group when SO(10) spontaneously breaks to $SU(3)\times SU(2)\times U(1)$. We comment upon the consequences of the sparticle mass spectrum for collider searches for supersymmetry. One implication of SO(10) unification is that the light bottom squark can be by far the lightest of the squarks. This motivates a dedicated search for bottom squark pair production at $p\bar{p}$ and $e^+e^-$ colliders.

hep-ph↗

arXiv1999

Supersymmetry Unification Predictions for M_top V_cb and tan(beta)

We study the predictions for M_top, tan(beta) and V_cb in a popular texture ansatze for the fermion mass matrices. We do this both for the Minimal Supersymmetric Standard Model (MSSM) and for the simplest model (MSSM-BRpV) where a bilinear R-Parity violating term is added to the superpotential. We find that taking the experimental values for M_top and V_cb at 99 % C.L. and the GUT relations h_b=h_tau and (V_cb)^2=h_c/h_t within 5 %, the large tan(beta) solution, characteristic in the MSSM with bottom--tau unification, becomes disallowed. In contrast the corresponding allowed region for the MSSM-BRpV is slightly larger. We also find that important modifications occur if we relax the texture conditions at the GUT scale. For example, if the GUT relations are imposed at 40 %, the large tan(beta) branch in the MSSM becomes fully allowed. In addition, in MSSM-BRpV the whole tan(beta)-M_top plane become allowed, finding unification at any value of tan(beta).

hep-ph↗

arXiv1998

Charged Higgs Mass Bounds from b -> s gamma in a Bilinear R-Parity Violating Model

The experimental measurement of $B(b \to sγ)$ imposes important constraints on the charged Higgs boson mass in the MSSM. If squarks are in the few TeV range, the charged Higgs boson mass in the MSSM must satisfy $m_{H^{\pm}} \gsim 440$ GeV. For lighter squarks, then light charged Higgs bosons can be reconciled with $B(b \to sγ)$ only if there is also a light chargino. In the MSSM if we impose $m_{χ^{\pm}_1}>90$ GeV then we need $m_{H^{\pm}} \gsim 110$ GeV. We show that by adding bilinear R--Parity violation (BRpV) in the tau sector, these bounds are relaxed. The bound on $m_{H^{\pm}}$ in the MSSM--BRpV model is $\gsim 340$ GeV for the the heavy squark case and $m_{H^{\pm}} \gsim 75$ GeV for the case of light squarks. In this case the charged Higgs bosons would be observable at LEP II. The relaxation of the bounds is due mainly to the fact that charged Higgs bosons mix with staus and they contribute importantly to $B(b \to sγ)$.

hep-ph↗

arXiv1998

Tau Lepton Mixing with Charginos and its Effects on Chargino Searches at e+e- Colliders

In bilinear R-Parity violating models where a term ε_3L_3H_2 is introduced in the superpotential, the tau lepton can mix with charginos. We show that this mixing is fully compatible with LEP1 precision measurements of the Zττand Wτν_τcouplings even for large values of ε_3 and of the induced vacuum expectation value v_3 of the tau-sneutrino. The single production of charginos at e+e- colliders is possible in this case and we present numerical values of the cross-section at LEP1, LEP2 and an NLC. We find maximum values of 10 pb at LEP1 and 1 fb at NLC, while the corresponding values at LEP2 are too small to observe.

hep-ph↗

arXiv1998

Seesaw Majoron Model of Neutrino Mass and Novel Signals in Higgs Boson Production at LEP

We perform a careful study of the neutral scalar sector of a model which includes a singlet, a doublet, and a triplet scalar field under $SU(2)$. This model is motivated by neutrino physics, since it is simply the most general version of the seesaw model of neutrino mass generation through spontaneous violation of lepton number. The neutral Higgs sector contains three CP-even and one massive CP-odd Higgs boson $A$, in addition to the massless CP-odd majoron $J$. The weakly interacting majoron remains massless if the breaking of lepton number symmetry is purely spontaneous. We show that the massive CP-odd Higgs boson may invisibly decay to three majorons, as well as to a CP-even Higgs $H$ boson plus a majoron. We consider the associated Higgs production $e^+e^- \to Z \to H A$ followed by invisible decays $A \to JJJ$ and $H \to JJ$ and derive the corresponding limits on masses and coupling that follow from LEP I precision measurements of the invisible Z width. We also study a novel $b \bar{b} b\bar{b}p\!\!\!/_T$ signal predicted by the model, analyse the background and perform a Monte-Carlo simulation of the signal in order to illustrate the limits on Higgs boson mass, couplings and branching ratios that follow from that.

hep-ph↗