arXiv subjects

Oscar Vives

Publications and source records attributed to Oscar Vives.

28 records · Page 2Linked to original sources

arXiv2006

Analysis of enhanced tan(beta) corrections in MFV GUT scenarios

We analyse a minimal supersymmetric standard model (MSSM) taking a minimal flavour violation (MFV) structure at the GUT scale. We evaluate the parameters at the electroweak scale taking into account the full flavour structure in the evolution of the renormalization group equations. We concentrate mainly on the decay Bs -> mu mu and its correlations with other observables like b -> s gamma, b -> s l l, Delta M_Bs and the anomalous magnetic moment of the muon. We restrict our analysis to the regions in parameter space consistent with the dark matter constraints. We find that the BR(Bs -> mu mu) can exceed the current experimental limit in the regions of parameter space which are allowed by all other constraints thus providing an additional bound on supersymmetric parameters. This holds even in the constrained MSSM. Assuming an hypothetical measurement of BR(Bs -> mu mu) ~ 10^-7 we analyse the predicted MSSM spectrum and flavour violating decay modes of supersymmetric particles which are found to be small.

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arXiv2005

Kahler corrections and softly broken family symmetries

Spontaneously broken family symmetry provides a promising origin for the observed quark and lepton mass and mixing angle structure. In a supersymmetric theory such structure comes from a combination of the contributions from the superpotential and the Kähler potential. The superpotential effects have been widely studied but relatively little attention has been given to the effects of the Kähler sector. In this paper we develop techniques to simplify the analysis of such Kähler effects. Using them we show that in the class of theories with an hierarchical structure for the Yukawa couplings the Kähler corrections to both the masses and mixing angles are subdominant. This is true even in cases that texture zeros are filled in by the terms coming from the Kähler potential.

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arXiv2005

Understanding the differences in neutrino and charged-fermion flavour structures

We present a new mechanism to explain naturally and through a common flavour symmetry the mildly hierarchical neutrino masses with large mixings and the hierarchical Yukawa matrices with small mixing angles. Although this mechanism is not linked to a particular flavour symmertry, it is particularly simple in the framework of a SU(3) flavour symmetry. In this model, we obtain exactly maximal atmospheric mixing, large although not maximal solar mixing and a normal neutrino hierarchy. All neutrino parameters are basically fixed. For instance, we predict that the angle $θ_{13}$ comes entirely from the charged lepton sector and, using the difference of the solar angle from maximality, we can fix the mass of lightest neutrino.

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arXiv2004

Massive Neutrinos and Flavour Violation

In spite of the large lepton flavour violation (LFV) observed in neutrino oscillations, within the Standard Model, we do \textit{not} expect any visible LFV in the charged lepton sector ($μ\to e, γ$, $τ\to μ, γ$, etc.). On the contrary, the presence of new physics close to the electroweak scale can enhance the amplitudes of these processes. We discuss this in general and focus on a particularly interesting case: the marriage of low-energy supersymmetry (SUSY) and seesaw mechanism for neutrino masses (SUSY seesaw). Several ideas presented in this context are reviewed both in the bottom-up and top-down approaches. We show that there exist attractive models where the rate for LFV processes can attain values to be probed in pre-LHC experiments.

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arXiv2004

Spontaneous CP violation and Non-Abelian Family Symmetry in SUSY

We analyse the properties of generic models based on an SU(3) family symmetry providing a full description of quark charged lepton and neutrino masses and mixing angles. We show that a precise fit of the resulting fermion textures is consistent with CP being spontaneously broken in the flavour sector. The CP violating phases are determined by the scalar potential and we discuss how symmetries readily lead to a maximal phase controlling CP violation in the quark sector. In a specific model the CP violation to be expected in the neutrino sector is related to that in the quark sector and we determine this relation for two viable models. In addition to giving rise to the observed structure of quark and lepton masses this class of model solves both the CP and flavour problems normally associated with supersymmetric models. The flavour structure of the soft supersymmetry breaking terms is controlled by the family symmetry and we analyse some of the related phenomenological implications.

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arXiv2003

Seesaw and Lepton Flavour Violation in SUSY SO(10)

That $μ\to e, γ$ and $τ\to μ,γ$ are sensitive probes of SUSY models with a see-saw mechanism is a well accepted fact. Here we propose a `top-down' approach in a general SUSY SO(10) scheme. In this framework, we show that at least one of the neutrino Yukawa couplings is as large as the top Yukawa coupling. This leads to a strong enhancement of these leptonic flavour changing decay rates. We examine two `extreme' cases, where the lepton mixing angles in the neutrino Yukawa couplings are either small (CKM-like) or large (PMNS-like). In these two cases, we quantify the sensitivity of leptonic radiative decays to the SUSY mass spectrum. In the PMNS case, we find that the ongoing experiments at the B-factories can completely probe the spectrum up to gaugino masses of 500 GeV (any tan $β$). Even in the case of CKM-like mixings, large regions of the parameter space will be probed in the near future, making these two processes leading candidates for indirect SUSY searches.

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arXiv2002

F-flatness and universality in broken Supergravity

We show that in a broken supergravity theory any field that acquires a vacuum expectation value obtains at the same time a non vanishing F-term whose natural size is given by $<θ> m_{3/2}$. These F-terms contribute unsuppressed to the trilinear couplings and have observable effects in the low energy phenomenology. We show that μ--> e γdecays can receive large contributions from this source at the level of current experimental bounds. Therefore this decay may provide the first clue of the structure of the soft breaking sector with the proposed experiments in the near future.

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arXiv2002

CP violation in realistic String Models with family universal anomalous U(1)

The characteristic property of the Z2XZ2 orbifold compactification is the cyclic permutation symmetry between the three twisted sectors. We discuss how this property, which is retained in a class of realistic free fermionic string models, may be instrumental in enabling fermion mass hierarchy while ensuring sfermion mass degeneracy, irrespective of the dominant source of supersymmetry breaking. The cyclic symmetry is reflected in some models in the existence of a family universal anomalous U(1)_A. We analyze the FCNC and CP violation effects in a model with a dominant U(1)_A SUSY breaking. In this theories, new sources of FC are always suppressed with respect to the average sfermion masses. We make a phenomenological analysis of these effects and find that in most of the cases they are in qualitative agreement with the phenomenological limits. The most sensitive low-energy observables to these new FC sources are the $ε_K$ parameter, measuring indirect CP violation in neutral kaon mixing and EDMs. These observables set important constraints on the structure of the sfermion mass matrices, but do not require a large fine-tuning of the initial parameters and can be satisfied in most realistic constructions.

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arXiv2000

New Physics behind the Standard Model's door?

We review the main reasons pushing us beyond the SM and we argue in favor of new physics at the electroweak scale (hence experimentally accessible at present or near-future machines). We focus on the appealing possibility that such new physics is given by a supersymmetric (SUSY) extension of the SM. We discuss the minimal case, Constrained Minimal Supersymmetric SM, and more general (maybe more natural) cases where some of the drastic assumptions of the CMSSM are dropped. In particular, in these lectures we focus on CP violation and its relation to flavor physics in the SUSY context. CP constrains the low-energy SUSY extensions of the SM, but, at the same time, it provides new powerful tool for indirect SUSY searches.

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arXiv2000

EDM-free supersymmetric CP violation with non-universal soft terms

Non-universality in the soft breaking terms is a common feature in most superstring inspired SUSY models. This property is required to obtain sizeable CP violation effects from SUSY and, on the other hand, can be used to avoid the Electric Dipole Moment constraints. We take advantage of these qualities and explore a class of SUSY models based on type I string theory where scalar masses, gaugino masses and trilinear couplings are non-universal. In this framework, we show that, in the presence of large SUSY phases, the bounds on the Electric Dipole Moments can be controled without fine-tuning. At the same time, we find that these phases, free from EDM constraints, lead to large contributions to the observed CP phenomena in Kaon system and, in particular, to direct CP violation in epsilon'/epsilon.

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