arXiv subjects

M. Bastero-Gil

Publications and source records attributed to M. Bastero-Gil.

26 records · Page 2Linked to original sources

arXiv1999

F-term Hybrid Inflation in Effective Supergravity Theories

We show that a particular class of effective low energy supergravity theories motivated by string theory can provide a promising framework for models of hybrid inflation in which the potential energy which drives inflation originates from the F-term of the effective supergravity theory. In the class of models considered the inflaton is protected from receiving mass during inflation by a generalisation of the Heisenberg symmetry present in no-scale supergravity models. The potential during inflation takes the positive definite form $V\sim |F_S|^2 + |F_T|^2 -3$, which allows the possibility that $V\ll m_{3/2}^2 M_P^2$ through the cancellation of the positive dilaton and moduli contribution against the negative term. We discuss a toy example where this is realised, then describe the application of this result to realistic models focusing on a particular example in which the $μ$ problem and the strong CP-problem are addressed.

hep-ph↗

arXiv1999

A Next-to-Minimal model of Hybrid Inflation in Effective Supergravity Theories

We propose a model of inflation based on a simple variant of the NMSSM, called $ϕ$NMSSM where the additional singlet $ϕ$ plays the role of the inflaton in hybrid (or inverted hybrid) type models. The $ϕ$NMSSM solves the $μ$ problem of the MSSM via the vacuum expectation value of the gauge singlet N, but also solves the strong CP problem through an approximate Peccei-Quinn symmetry. The potential energy which drives inflation originates from the F-term of the effective supergravity theory which result from a generic string theory. In the class of models considered the inflaton is protected from receiving mass during inflation by a Heisenberg symmetry, avoiding the $η$ problem.

hep-ph↗

arXiv1998

A Next-to-Minimal Supersymmetric Model of Hybrid Inflation

We propose a model of inflation based on a simple variant of the NMSSM, called $ϕ$NMSSM, where the additional singlet $ϕ$ plays the role of the inflaton in hybrid (or inverted hybrid) type models. As in the original NMSSM, the $ϕ$NMSSM solves the $μ$ problem of the MSSM via the VEV of a gauge singlet $N$, but unlike the NMSSM does not suffer from domain wall problems since the offending $Z_3$ symmetry is replaced by an approximate Peccei-Quinn symmetry which also solves the strong CP problem, and leads to an invisible axion with interesting cosmological consequences. The PQ symmetry may arise from a superstring model with an exact discrete $Z_3 \times Z_5$ symmetry after compactification. The model predicts a spectral index $n=1$ to one part in $10^{12}$.

hep-ph↗

arXiv1998

A Next-to-Minimal Supersymmetric Model of Hybrid Inflation

In this talk we discuss a model of inflation based on a simple variant of the NMSSM, called $ϕ$NMSSM \cite{phiNMSSM}, where the additional singlet $ϕ$ plays the role of the inflaton in hybrid (or inverted hybrid) type models. As in the original NMSSM, the $ϕ$NMSSM solves the $μ$ problem of the MSSM via the VEV of a gauge singlet $N$, but unlike the NMSSM does not suffer from domain wall problems since the offending $Z_3$ symmetry is replaced by an approximate Peccei-Quinn symmetry which also solves the strong CP problem, and leads to an invisible axion with interesting cosmological consequences. The model predicts a spectral index $n=1$ to one part in $10^{12}$.

hep-ph↗

arXiv1996

Perturbative Unification and Low Energy Precision Data

More precise unification predictions require going beyond the lowest order, including 2-loop running of the couplings and a correct treatment of threshold effects. Here we revised two different approaches to deal with light thresholds, based on different choices of the renormalization scheme, \bar{MS} and effective couplings. We show the equivalence of both approaches in making predictions when thresholds are taking properly into account.

hep-ph↗

arXiv1996

Magnitude of R-parity violation in String Inspired GUTs

The nature of R-parity violating interactions in two classes of string inspired supersymmetric grand unified theories (SISUSY GUT), based on the gauge groups $SO(10)$ (and its subgroup $SU(2)_L\times SU(2)_R\times SU(4)_c\equiv G_{224}$) as well as $[SU(3)]^3$, are discussed and their strengths are related to the ratio of symmetry breaking scales present in the model. We first argue that for the R-parity violating couplings $λ_{R\!\!\!/}$ to be suppressed to the desired level, the $B-L$ local symmetry must break at an intermediate scale $M_{B-L}$ since $λ_{R\!\!\!/} =M_{B-L}/M_{GUT}$. We then construct scenarios where such intermediate scales arise being consistent with gauge coupling unification in a two-loop renormalization group study. In the resulting $SO(10)$ models, higher-dimensional-operator-induced R-parity violating couplings are potentially large (except in one case), and are therefore inconsistent with limits on the proton life time unless the couplings associated with the higher dimensional terms are fine tuned to very small values. However, the $[SU(3)]^3$ and $G_{224}$ models can be consistent if a certain class of quark-lepton coupling in the superpotential is forbidden by a discrete summetry (unrelated to R-parity). An interesting prediction of these models is neutron-anti-neutron oscillation with observable strength.

hep-ph↗

arXiv1993

Influence of Light and Heavy Thresholds on SUSY Unification

In this paper we study and compare susy unification using two different approaches in order to take into account the effect of light particle thresholds on the evolution of gauge couplings: the step--function approximation, on the one hand, and a mass dependent procedure, which gives a more accurate description of the dependence of the results on the masses, on the other. We also include the effect of heavy thresholds, when $SU(5)$ is chosen as the unifying group. We find that the mass--dependent procedure excludes scenarios where all susy masses are below $1\;TeV$, and favors a value of $α_3(m_Z)$ near its upper experimental bound, contrary to the results obtained with the step--function approximation. We underline the dependence of the results on the procedure chosen to deal with light thresholds.

hep-ph↗

arXiv1993

Threshold Effects And Perturbative Unification

We discuss the effect of the renormalization procedure in the computation of the unification point for running coupling constants. We explore the effects of threshold--crossing on the $β$--functions. We compute the running of the coupling constants of the Standard Model, between $m_Z$ and $M_P$, using a mass dependent subtraction procedure, and then compare the results with $\bar{MS}$, and with the $θ$-- function approximation. We also do this for the Minimal Supersymmetric extension of the Standard Model. In the latter, the bounds on susy masses that one obtains by requiring perturbative unification are dependent, to some extent, on the procedure.

hep-ph↗