arXiv subjects

Marco A. Diaz

Publications and source records attributed to Marco A. Diaz.

33 records · Page 2Linked to original sources

arXiv1998

Charged Higgs Boson and Stau Phenomenology in the Simplest R-Parity Breaking Model

We consider the charged scalar boson phenomenology in the simplest effective low-energy R-parity breaking model characterized by a bilinear violation of R-parity in the superpotential. This induces a mixing between staus and the charged Higgs boson. We show that the charged Higgs boson mass can be lower than expected in the MSSM, even before including radiative corrections. We also study the charged scalar boson decay branching ratios and show that the R-parity violating decay rates can be comparable or even bigger than the R-parity conserving ones. Moreover, if the stau is the LSP it will have only decays into standard model fermions. These features could have important implications for charged supersymmetric scalar boson searches at future accelerators.

hep-ph↗

arXiv1998

Gauge and Yukawa Unification with Broken R-Parity

We study gauge and Yukawa coupling unification in the simplest extension of the Minimal Supersymmetric Standard Model (MSSM) which incorporates R-Parity violation through a bilinear superpotential term. Contrary to what happens in the MSSM, we show that bottom-tau unification at the scale M_GUT where the gauge couplings unify can be achieved for any value of tan(beta) by choosing appropriately the sneutrino vacuum expectation value. In addition, we show that bottom-tau-top unification occurs in a slightly wider tan(beta) range than in the MSSM.

hep-ph↗

arXiv1998

Radiatively Corrected Chargino Pair Production at LEP2

One-loop radiative corrections to the production cross section of a pair of light charginos in e+e- colliders are calculated within the MSSM. Top and bottom quarks and squarks are considered in the loops, and they are renormalized using the MS-bar scheme. If the center of mass energy is equal to 192 GeV, positive corrections typically of 10% to 15% are found when the squark mass parameters are equal to 1 TeV.

hep-ph↗

arXiv1997

Radiative Corrections to Chargino Production in Electron-Positron Collisions

We discuss the one-loop radiative corrections to the reaction e^+ e^- -> X^+_a X^-_b, for a,b=1,2 where X^+_{1,2} are the charginos of the minimal supersymmetric standard model. We calculate the leading one loop radiative corrections involving loops of top, stop, bottom and sbottom quarks, working in the MS-bar scheme. At LEP2 we find positive radiative corrections typically of 10% to 15% and with a maximum value of approximately 30% if the squark mass parameters are of the order of 1 TeV. If \sqrt{s}=500 GeV we find smaller corrections but they can be also negative, with extreme values of 13% and -4%. For a center of mass given by \sqrt{s}=2 TeV we find larger corrections, with typical values between 20% and -20%.

hep-ph↗

arXiv1997

Minimal Supergravity with R-Parity Breaking

We show that the minimal R-parity breaking model characterized by an effective bilinear violation of R-parity in the superpotential is consistent with minimal N=1 supergravity unification with radiative breaking of the electroweak symmetry and universal scalar and gaugino masses. This one-parameter extension of the MSSM-SUGRA model provides therefore the simplest reference model for the breaking of R-parity and constitutes a consistent truncation of the complete dynamical models with spontaneous R-parity breaking proposed previously. We comment on the lowest-lying CP-even Higgs boson mass and discuss its minimal N=1 supergravity limit, determine the ranges of $\tanβ$ and bottom quark Yukawa couplings allowed in the model, as well as the relation between the tau neutrino mass and the bilinear R-parity violating parameter.

hep-ph↗

arXiv1996

Chargino Production at LEP2 in a Supergravity Model

In the framework of a particular supergravity model which provides a natural solution to the $μ$--problem we show how the discovery of a chargino at LEP2 and the measurement of its mass and production cross--section, together with the measurement of the mass of the lightest neutralino, would determine the entire Higgs and SUSY spectrum. We give detailed predictions for the Higgs and SUSY spectrum as a function of the chargino production cross--section, for constant values of the lightest chargino and gluino masses.

hep-ph↗

arXiv1995

Selectron Pair Production in e+e- Colliders and the Supergravity Spectrum

Selectrons may be produced in pairs at LEPII if their mass is less than about 100 GeV. Preferably, they decay into the lightest neutralino plus an electron. In a scenario where selectrons are observed at LEPII, we show that: (i) in a first stage where experimental errors are large, the measurement of the total cross section of selectron pair production, the selectron mass, and the lightest neutralino mass, allow us to validate or rule out the Minimal Supergravity Model in its simplest form, and that (ii) in a second stage where precision measurements are available, the value of $\tanβ$ can be determined together with the rest of the parameters that specify the Minimal Supergravity Model and, with them, the entire supersymmetric spectrum can be calculated. We include experimental constraints from sparticle searches, $Z$--pole physics, stability of the lightest supersymmetric particle (LSP) and the decay $b\rightarrow sγ$. In these scenarios, small values of $\tanβ$ and negative values of $μ$ are preferred, and the lightest Higgs mass satisfies $m_h<110$ GeV, which makes it likely to be detected at LEPII.

hep-ph↗

arXiv1995

Radiative Corrections to Charged Higgs Production in e+ e- Colliders

We study one loop electroweak corrections to the production of a pair of charged Higgs bosons through an intermediate $Z$-boson or photon. In particular, we consider the effects of graphs with top and bottom quarks and squarks in the loop within the context of the Minimal Supersymmetric Model. We find that the corrections can be considerable, and typically are of the order of 10\% to 20\%.

hep-ph↗

arXiv1995

Charginos and Neutralinos at LEPII

We show that LEPII will either discover charginos and neutralinos, or enable a very stringent upper limit to be placed on $\tan β$ as a function of the gluino mass. The only assumption we make is the existence of some unified model which breaks down to the minimal supersymmetric standard model below the unification scale. In such a framework we discuss how the discovery of a chargino at LEPII and the measurement of its mass and production cross-section, together with the measurement of the mass of the lightest neutralino, would enable the gluino mass, $\tan β$ and $μ$ to be predicted, up to a possible ambiguity in the sign of $μ$ which we discuss.

hep-ph↗

arXiv1994

The Higgs Mass as the Discriminator of Electroweak Models

In the Minimal Supersymmetric Model (MSSM) and the Next to Minimal Supersymmetric Model [(M+1)SSM], an upper bound on the lightest higgs mass can be calculated. On the other hand, vacuum stability implies a lower limit on the mass of the higgs boson in the Standard Model (SM). We find that a gap exists for $m_t \stackrel{>}{\sim} 165$ GeV between the SM and both the MSSM and the (M+1)SSM bounds. Thus, if the new top quark mass measurement by CDF remains valid, a first measurement of the higgs mass will serve to exclude either the SM or the MSSM/(M+1)SSM higgs sectors. In addition, we discuss Supersymmetric Grand Unified Theories, other extentions of the SM, the discovery potential of the lightest higgs, and the assumptions on which our conclusions are based.

hep-ph↗

arXiv1994

Higgs Mass Bounds Separate Models of Electroweak Symmetry Breaking

Vacuum stability implies a lower limit on the mass of the higgs boson in the Standard Model (SM). In contrast, an upper limit on the lightest higgs mass can be calculated in supersymmetric (susy) models. The main uncertainty in each limit is the value of the top mass, which may now be fixed by the recent CDF result. We study the possibility that these bounds do not overlap, and find that (i) a mass gap emerges at $m_t\sim 160$ GeV between the SM and the Minimal Susy Standard Model (MSSM); and between the SM and the Minimal plus Singlet Susy Model [(M+1)SSM] if the independent scalar self--coupling of the latter is perturbatively small or if the $\tanβ$ parameter is large; this gap widens with increasing $m_t$; (ii) there is no overlap between the SM and the MSSM bounds at even smaller values of $m_t$ for the $\tanβ$ value ($\sim 1$--2) preferred in Supersymmetric Grand Unified Theories. Thus, if the new top mass measurement remains valid, a measurement of the first higgs mass will serve to exclude either the SM or MSSM/(M+1)SSM higgs sectors. In addition, we discuss the upper bound on the lightest higgs mass in susy models with an extended higgs sector, and in models with a strongly interacting higgs sector. Finally, we comment on the discovery potential for the lightest higgses in these models.

hep-ph↗

arXiv1994

Decays of a fermiophobic Higgs

We explore the phenomenology of a fermiophobic Higgs: a Higgs whose couplings to fermions are suppressed. We calculate the branching ratios of a Higgs decaying to $γγ$, $W^*W^*$, $Z^*Z^*$, $Zb\bar b$, $Zγ$, $γb\bar b$, and final states involving vector mesons like $Υ$, $J/Ψ$ and $ρ$. In order to calculate these branching ratios we perform a complete one-loop renormalization of the vertices $HZγ$ and $Hγγ$. The decay mode $H\rightarrow γγ$ is near unity for a Higgs below the $W$ mass, which provides a clean way of discovering a light fermiophobic Higgs. Interesting modes involving the vector mesons $Z$, $γ$, $ρ$, $J/Ψ$, and $Υ$ are carefully analyzed.

hep-ph↗

arXiv1993

Top Quark and Charged Higgs: Linked by Radiative Corrections

Some aspects of the phenomenology of the top quark and the charged Higgs are studied, emphasizing relations due to radiative corrections. Production mechanisms at the SSC are mentioned, and decay modes are analyzed including radiative corrections to the charged Higgs mass and couplings. The constraints due to the decay b-> s γare discussed. Calculations are performed in the context of the Minimal Supersymmetric Model.

hep-ph↗

arXiv1993

Constraints on Supersymmetry due to b -> s γ: an Improved Calculation

The calculation of the one-loop induced decay rate b -> s γis improved by including radiative corrections to the charged Higgs mass and to the charged-Higgs-fermion-fermion vertex. It is shown how the radiative corrections modify the excluded zone in the \tanβ-m_A plane, imposed by the non-observation of this decay. In particular, a light CP-odd Higgs at large \tanβbecomes allowed.

hep-ph↗

arXiv1993

Electroweak Corrections to the Supersymmetric Charged Higgs Fermionic Decay

One-loop radiative corrections to the charged Higgs coupling to two fermions and to the charged Higgs fermionic decay are studied. A renormalization scheme is proposed including the definition of the parameter $\tanβ$ through the coupling of the CP-odd Higgs boson to a charged lepton pair. Loops including top and bottom quarks and squarks are considered using the unitary gauge. Large corrections to the coupling are found when there is a substantial mixing in the squark mass matrix, but these corrections are suprress in the decay rate. Interesting applications to rare processes are discussed.

hep-ph↗