arXiv subjects

Alex Pomarol

Publications and source records attributed to Alex Pomarol.

At least 73 records · Page 4Linked to original sources

arXiv2000

Bulk Fields and Supersymmetry in a Slice of AdS

Five-dimensional models where the bulk is a slice of AdS have the virtue of solving the hierarchy problem. The electroweak scale is generated by a ``warp'' factor of the induced metric on the brane where the standard model fields live. However, it is not necessary to confine the standard model fields on the brane and we analyze the possibility of having the fields actually living in the slice of AdS. Specifically, we study the behaviour of fermions, gauge bosons and scalars in this geometry and their implications on electroweak physics. These scenarios can provide an explanation of the fermion mass hierarchy by warp factors. We also consider the case of supersymmetry in the bulk, and analyze the conditions on the mass spectrum. Finally, a model is proposed where the warp factor generates a small (TeV) supersymmetry-breaking scale, with the gauge interactions mediating the breaking to the scalar sector.

hep-ph↗

arXiv1999

Gauge bosons in a five-dimensional theory with localized gravity

We consider the possibility of gauge bosons living in the recently proposed five-dimensional theory with localized gravity. We study the mass spectrum of the Kaluza-Klein (KK) excitations of the gauge fields and calculate their couplings to the boundaries of the fifth dimension. We find a different behaviour from the case of the graviton. In particular, we find that the massless mode is not localized in the extra dimension and that the KK excitations have sizeable couplings to the two boundaries. We also discuss possible phenomenological implications for the case of the standard model gauge bosons.

hep-ph↗

arXiv1999

Sparticle Masses from the Superconformal Anomaly

We discuss a recently proposed scenario where the sparticle masses are purely mediated by gravity through the superconformal anomaly. This scenario elegantly evades the supersymmetric flavor problem since soft masses, like the anomaly, are not directly sensitive to ultraviolet physics. However, its minimal incarnation fails by predicting tachyonic sleptons. We study the conditions for decoupling of heavy threshold effects and how these conditions are evaded. We use these results to build a realistic class of models where the non-decoupling effects of ultra-heavy vectorlike matter fields eliminate the tachyons. These models have a flavor invariant superspectrum similar to that of gauge mediated models. They, however, differ in several aspects: the gaugino masses are not unified, the colored sparticles are not much heavier than the others, the mu-problem is less severe and the gravitino mass is well above the weak scale, m_{3/2} \sim 10 TeV. We also show that in models where an R-symmetry can be gauged, the associated D-term gives rise to soft terms that are similarly insensitive to the ultraviolet.

hep-ph↗

arXiv1999

Effects of SM Kaluza-Klein excitations on electroweak observables

The presence of an extra dimension of size R \approx TeV^{-1} introduces a tower of Kaluza-Klein gauge boson excitations that affects the standard model (SM) relations between electroweak observables. The mixing of the W and Z bosons with their excitations changes their masses and couplings to fermions. This effect depends on the Higgs field, which may live in the bulk of the extra dimension, on its boundary, or may be a combination of both types of fields. We use high-precision electroweak data to constrain 1/R. We find limits from 1 to 3 TeV from different observables, with a model independent bound of 2.5 TeV.

hep-ph↗

arXiv1997

Anomalous U(1), Gauge-Mediated Supersymmetry Breaking and Higgs as Pseudo-Goldstone Bosons

We study the breaking of supersymmetry in models with anomalous U(1). These models are simple to construct and contain natural candidates for being the messengers of gauge-mediated supersymmetry breaking. When some of the ordinary matter fields transform under the anomalous U(1), we find a hybrid scenario in which the U(1) and the gauge interactions mediate the breaking of supersymmetry. This leads to a hierarchy of soft masses between the charged and neutral fields and provides a solution to the $μ$-problem. Among these models, we present a scenario in which the Higgs arises as a pseudo-Goldstone boson. This scenario naturally allows for values of the $μ$-term and the scalar soft masses larger than the weak scale.

hep-ph↗

arXiv1997

Supersymmetry Breaking with Vanishing F-terms in Supergravity Theories

In conventional supergravity theories, supersymmetry is broken by a non-zero F-term, and the cosmological constant is fine tuned to zero by a constant in the superpotential W. We discuss a class of supergravity theories with vanishing F-terms but $W \not= 0$ being generated dynamically. The cosmological constant is assumed to be cancelled by a non-zero D-term. In this scenario the gravity-mediated soft masses depend only on a single parameter, the gravitino mass. They are automatically universal, independently of the Kahler metric, and real. Thus, dangerous flavor or CP violating interactions are suppressed. Unlike in conventional supergravity models, the Polonyi problem does not arise.

hep-ph↗

arXiv1997

Dynamical determination of the Supersymmetric Higgs mass

Considering the supersymmetric Higgs mass ($μ$-parameter) as a dynamical variable to be determined by minimizing the energy, we predict its value as a function of the soft masses of the potential. We find that $μ$ has a nonzero value close to the weak scale. This scenario offers a simultaneous solution to the doublet-triplet splitting problem and to the $μ$-problem. We discuss its viability in theories with gauge mediated supersymmetry breaking.

hep-ph↗

arXiv1996

Advantages and Disadvantages of Supersymmetry Breaking at Low Energies

The breaking of supersymmetry is usually assumed to occur in a hidden sector. Two natural candidates for the supersymmetry breaking transmission from the hidden to the observable sector are gravity and the gauge interactions. Only the second one allows for supersymmetry breaking at low energies. I show how the two candidates deal with the flavor and the $μ$-problem; I also briefly comment on the doublet-triplet and dark matter problem.

hep-ph↗

arXiv1996

Anomalous U(1) as a mediator of Supersymmetry Breaking

We point out that an anomalous gauge U(1) symmetry is a natural candidate for being the mediator and messenger of supersymmetry breaking. It facilitates dynamical supersymmetry breaking even in the flat limit. Soft masses are induced by both gravity and the U(1) gauge interactions giving an unusual mass hierarchy in the sparticle spectrum which suppresses flavor violations. This scenario does not suffer from the Polonyi problem.

hep-ph↗

arXiv1996

Horizontal Symmetries for the Supersymmetric Flavor Problem

The heaviness of the third family fermions and the experimental absence of large flavor violating processes suggest, in supersymmetric theories, that the three families belong to a $2+1$ representation of a horizontal symmetry $G_H$. In this framework, we discuss a class of models based on the group U(2) that describe the fermion flavor structure and are compatible with an underlying GUT. We study the phenomenology of these models and focus on two interesting scenarios: In the first one, the first and second family scalars are assumed to be heavier than the weak scale allowing for complex soft supersymmetry breaking terms. In the second one, all the CP-violating phases are assumed to be small. Both scenarios present a rich phenomenology in agreement with constraints from flavor violating processes and electric dipole moments.

hep-ph↗

arXiv1995

Mass Degeneracy of the Higgsinos

The search for charginos and neutralinos at LEP2 can become problematic if these particles are almost mass degenerate with the lightest neutralino. Unfortunately this is the case in the region where these particles are higgsino-like. We show that, in this region, radiative corrections to the higgsino mass splittings can be as large as the tree-level values, if the mixing between the two stop states is large. We also show that the degree of degeneracy of the higgsinos substantially increases if a large phase is present in the higgsino mass term $μ$.

hep-ph↗

arXiv1995

SHOULD SPARTICLE MASSES UNIFY AT THE GUT SCALE?

Gauge and Yukawa (for the third family) coupling unification seem to be the best predictions of the grand-unified theories (GUTs). In supersymmetric GUTs, one also expects that the sparticle masses unify at the GUT scale (for sparticles embedded in the same GUT multiplet). I show under what circumstances GUTs do not lead to sparticle mass unification. In particular, I give examples of SU(5) and SO(10) SUSY GUTs in which squarks and sleptons of a family have different tree-level masses at the unification scale. The models have interesting relations between Yukawa couplings. For example, I present an SO(10) GUT that allows for a large ratio of the top to bottom Yukawas, accounting for the large $m_t /m_b$. The splittings can also be induced in the Higgs soft masses and accommodate the electroweak breaking.

hep-ph↗

arXiv1995

Superfield Derivation of the Low-Energy Effective Theory of Softly Broken Supersymmetry

We analyze the soft supersymmetry breaking parameters obtained in grand unified theories after integrating out the heavy GUT-states. The superfield formalism greatly simplifies the calculations and allows us to derive the low-energy effective theory in the general case of non-universal and non-proportional soft terms by means of a few Feynman diagrams. We find new contributions not considered before. We discuss the implications for the destabilization of the gauge hierarchy, flavor violating processes and the non-unification of sparticle masses in unified theories.

hep-ph↗

arXiv1995

NON-UNIFIED SPARTICLE AND PARTICLE MASSES IN UNIFIED THEORIES.

We give examples of minimal extensions of the simplest SU(5) SUSY-GUT in which all squarks and sleptons of a family have different tree level masses at the unification scale. This phenomenon is general; it occurs when the quarks and leptons are the light remnants of a theory which contains extra heavy families at the unification scale. The examples have interesting relations between Yukawa couplings: In one model the ratio of the top to bottom Yukawas is as large as $\simeq 3$, partly accounting for the large $m_t /m_b$. Another gives $m_b/m_τ$ between 2/3 and 1; this relaxes the strict bounds on the top mass and neutrino properties that come from $b$--$τ$ unification. Still another allows $ m_s/m_μ$ to be between 1/6 and 1 and evades the potentially problematic GUT relation of $m_s=m_μ$. The final example has horizontal sparticle splittings in spite of the existence of horizontal symmetries.

hep-ph↗

arXiv1994

Non-Universal GUT Corrections to the Soft Terms and their Implications in Supergravity Models

Potentially large non-universal corrections to the soft supersymmetry breaking parameters arise from their evolution between the Planck and the grand-unification scales. We detail typical patterns of non-universality in GUT models, as well as elaborate on their propagation to the weak scale and on their low-energy implications. Possible corrections to the different scalar quark and lepton masses and the Higgs and the gaugino-Higgsino sector parameters are described in detail, and new allowed regions of the parameter space are pointed out. In particular, the patterns studied often lead to heavier Higgsinos and $t$-scalar. One-loop GUT threshold corrections to the soft parameters are also discussed and shown to be important.

hep-ph↗

arXiv1994

GUT effects in the soft supersymmetry breaking terms

In minimal supergravity theories the soft supersymmetry breaking (SSB) parameters are universal (flavor blind) near the Planck scale. Nevertheless, one often assumes universality at the grand-unification scale $M_{G} \approx 10^{16}$ GeV instead, and corrections to the SSB parameters arising from their evolution between the Planck and GUT scales are neglected. We study these corrections and show that large splittings between the scalar mass parameters can be induced at $M_{G}$. These effects are model dependent and lead to significant uncertainties in the low-energy predictions of supersymmetric models, in their correlations and in the allowed parameter space.

hep-ph↗

arXiv1994

Top Radiative Corrections in Non-minimal Standard Models

We derive the one-loop effective action induced by a heavy top in models with an extended Higgs sector. We use the effective action to analyze the top corrections to the $ρ$ parameter and to the Higgs-gauge boson couplings. We show that in models with $ρ\not=1$ at tree-level, one does not lose generally the bound on $m_t$ from the $ρ$ parameter.

hep-ph↗

arXiv1993

Energy Distribution of the Leptons in Top Decay to Charged Higgs

We analyze the energy distribution of the leptons coming from the top decay $t\ra b\hc,\ bW^+\ra bl^+ν$. The correlation between the lepton energy distribution and the top spin may be useful for distinguishing the $\hc$ signature from the $W$ background. Such a correlation can also be useful for disentangling the two different $\hc \bar tb$ couplings and determining the experimental value of $\tanβ$.

hep-ph↗