arXiv subjects

E. Torrente-Lujan

Publications and source records attributed to E. Torrente-Lujan.

52 records · Page 3Linked to original sources

arXiv2002

Relic Neutralino Density in Scenarios with Intermediate Unification Scale

We analyse the relic neutralino density in supersymmetric models with an intermediate unification scale. In particular, we present concrete cosmological scenarios where the reheating temperature is as small as $\cal{O}$ $1 - 1000$ MeV). When this temperature is associated to the decay of moduli fields producing neutralinos, we show that the relic abundance increases considerably with respect to the standard thermal production. Thus the neutralino becomes a good dark matter candidate with $0.1\lsim Ωh^2 \lsim 0.3$, even for regions of the parameter space where large neutralino-nucleon cross sections, compatible with current dark matter experiments, are present. This is obtained for intermediate scales $M_I\sim 10^{11}-10^{14}$ GeV, and moduli masses $m_ϕ\sim 100-1000$ GeV. On the other hand, when the above temperature is associated to the decay of an inflaton field, the relic abundance is too small.

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arXiv2001

Solar neutrino experiments and Borexino perspectives

We present an updated analysis of all the data available about solar neutrinos, including the charged current SNO results. The best fit of the data is obtained in the Large Mixing Angle region, but different solutions are still possible. We also study the perspectives of Borexino and conclude that this experiment, with a parallel analysis of total rate and day-night asymmmetry, should be able to discriminate between the different possible solutions.

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arXiv2001

Determination of the String Scale in D-Brane Scenarios and Dark Matter Implications

We analyze different phenomenological aspects of D-brane constructions. First, we obtain that scenarios with the gauge group and particle content of the supersymmetric standard model lead naturally to intermediate values for the string scale, in order to reproduce the value of gauge couplings deduced from experiments. Second, the soft terms, which turn out to be generically non universal, and Yukawa couplings of these scenarios are studied in detail. Finally, using these soft terms and the string scale as the initial scale for their running, we compute the neutralino-nucleon cross section. In particular we find regions in the parameter space of D-brane scenarios with cross sections in the range of $10^{-6}$--$10^{-5}$ pb, i.e. where current dark matter experiments are sensitive. For instance, this can be obtained for $\tanβ> 5$.

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arXiv2001

Muon anomalous magnetic moment in supersymmetric scenarios with an intermediate scale and nonuniversality

We analyze the anomalous magnetic moment of the muon (a_μ) in supersymmetric scenarios. First we concentrate on scenarios with universal soft terms. We find that a moderate increase of a_μ can be obtained by lowering the unification scale M_{GUT} to intermediate values 10^{10-12} GeV. However, large values of \tan βare still favored. Then we study the case of non-universal soft terms. For the usual value M_{GUT}~10^{16} GeV, we obtain a_μ in the favored experimental range even for moderate \tan βregions \tanβ~ 5$. Finally, we give an explicit example of these scenarios. In particular, we show that in a D-brane model, where the string scale is naturally of order 10^{10-12} GeV and the soft terms are non universal, a_μ is enhanced with low \tanβ.

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arXiv2000

Neutrino mass and oscillation as probes of physics beyond the Standard Model

We present a review of the present status of the problem of neutrino masses and mixing including a survey of theoretical motivations and models, experimental searches and implications of recently appeared solar and atmospheric neutrino data, which strongly indicate nonzero neutrino masses and mixing angles.

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arXiv2000

Initial Scales, Supersymmetric Dark Matter and Variations of Neutralino-Nucleon Cross Sections

The neutralino-nucleon cross section in the context of the MSSM with universal soft supersymmetry-breaking terms is compared with the limits from dark matter detectors. Our analysis is focussed on the stability of the corresponding cross sections with respect to variations of the initial scale for the running of the soft terms, finding that the smaller the scale is, the larger the cross sections become. For example, by taking $10^{10-12}$ GeV rather than $M_{GUT}$, which is a more sensible choice, in particular in the context of some superstring models, we find extensive regions in the parameter space with cross sections in the range of $10^{-6}$--$10^{-5}$ pb, i.e. where current dark matter experiments are sensitive. For instance, this can be obtained for $\tanβ\gsim 3$.

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arXiv2000

The $b\to sγ$ decay in SUSY models with non-universal A-terms

We analyse the predictions for the inclusive branching ratio for $b\to sγ$ decay in a class of string-inspired SUSY models with non-universal soft-breaking A-terms. These models are particularly interesting since the non-universality of the A-terms plays an important role in providing new significant contributions to CP violation effects in kaon physics while respecting the severe bounds on electric dipole moments. We show that $b\to sγ$ do not severely constrain the non-universality of these models. In particular, at low $\tanβ$ $(\tanβ\simeq 2)$, our predictions are close to the universal case. For large $\tanβ$ ($\tanβ\gsim 15$),the effect of non-universality is enhanced and stronger constraints hold. We find that the parameter regions which are important for generating sizeable contribution to $ε'/ε$, of order $2 \times 10^{-3}$, are not excluded.

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arXiv1999

Influence of solar chaotic magnetic fields on neutrino oscillations

We consider the effect of a random magnetic field in the convective zone of the Sun on resonant neutrino spin-flavour oscillations. The expected signals in the different experiments (SK, GALLEX-SAGE,Homestake) are obtained as a function of the level of noise, regular magnetic field and neutrino mixing parameters. Previous results obtained for small mixing and ad-hoc regular magnetic profiles are reobtained. We find that MSW regions are stable up to very large levels of noise (P=0.7-0.8) and they are acceptable from the point of view of antineutrino production. For strong noise any parameter region $(Δm^2, \sin^2 2θ)$ is excluded: this model of noisy magnetic field is not compatible with particle physics solutions to the SNP. scenario.

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arXiv1999

Bounds on the Solar Antineutrino total Flux and Energy spectrum from the SK experiment

A search for inverse beta decay electron antineutrinos has been carried out using the 825 days sample of solar data obtained at SK. The absence of a significant signal, that is, contributions to the total SK background and their angular variations has set upper bounds on a) the absolute flux of solar antineutrinos originated from ${}^8 B$ neutrinos $Φ_{\barν}({}^8 B)=< 1.8\times 10^5 cm^{-2} s^{-1}$ which is equivalent to an averaged conversion probability bound of P<3.5% (SSM-BP98 model) and b) their differential energy spectrum, the conversion probability is smaller than 8% for all $E_{e,vis}>6.5$ MeV going down the 5% level above $E_{e,vis}\approx 10$ MeV. It is shown that an antineutrino flux would have the net effect of enhancing the SK signal at {\em hep} neutrino energies. The magnitude of this enhancement would highly depend on the, otherwise rather uncertain, steepness of the solar neutrino spectrum at these energies.

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arXiv1999

The decay $b\to sγ$ and the charged Higgs boson mass without R-Parity

The experimental measurement of $B(b \to sγ)$ imposes important constraints on the charged Higgs boson mass in the MSSM. 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 $\gsim 200-250$ GeV for the the heavy squark limit. For lighter squarks, light charged Higgs bosons can be reconciled with $B(b \to sγ)$ only if there is also a light chargino. In the BRpV model if we impose $m_{χ^{\pm}_1}>90$ GeV $m_{H^{\pm}} \gsim 75$ GeV, around 30 GeV down from the MSSM. 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 $B(b \to sγ)$.

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arXiv1999

A Review on Neutrino Physics, Mass and Oscillations

We present a short review of the present status of the problem of neutrino masses and mixing including a survey of theoretical motivations and models, experimental searches and implications of recently appeared solar and atmospheric neutrino data, which strongly indicate nonzero neutrino masses. Such data apparently requires the existence of light sterile neutrino in addition to the three active ones and two-generation nearly maximal mixing.

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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

Neutrino Conversions in Solar Random Magnetic Fields

We consider the effect of a random magnetic field in the convective zone of the Sun superimposed to a regular magnetic field on resonant neutrino spin-flavour oscillations. We argue for the existence of a field of strongly chaotic nature at the bottom of the convective zone. In contrast to previous attempts we employ in addition a model motivated regular twisting magnetic field profile. In this scenario electron antineutrinos are produced through cascades like $ν_{eL}\to ν_{μL}\to \tildeν_{eR}$, The expected signals in the different experiments (SK,GALLEX-SAGE, Homestake) are obtained as a function of the level of noise, regular magnetic field and neutrino mixing parameters. Previous results obtained for small mixing and ad-hoc regular magnetic profiles are reobtained. We confirm the strong suppression for large part of the parameter space of the $\tildeν_{eR}$-flux for high energy boron neutrinos in agreement with present data of the SK experiment. We find that MSW regions ($Δm^2\approx 10^{-5}$ eV$^2$, both small and large mixing solutions) are stable up to very large levels of noise (P=0.7-0.8) but they are acceptable from the point of view of antineutrino production only for moderate levels of it ($P\approx 0.95$). For strong noise and reasonable regular magnetic field, any parameter region $(Δm^2, \sin^2 2θ)$ is excluded. As a consequence, we are allowed to reverse the problem and to put limits on r.m.s field strength and transition magnetic moments by demanding a particle physics solution to the SNP under this scenario.

hep-ph↗

arXiv1998

Solar Antineutrinos from Fluctuating Magnetic Fields at Kamiokande

We consider the effect of a strongly chaotic magnetic field at the narrow bottom of the convective zone of the Sun together with resonant matter oscillations on the production of electron Majorana antineutrinos. Even for moderate levels of noise, we show that it is possible to obtain a small but significant probability for $ν_e\to \barν_e$ conversions (1-3%) at the energy range 2-10 MeV for large regions of the mixing parameter space while still satisfying present (Super)-Kamiokande antineutrino bounds and observed total rates. In the other hand it would be possible to obtain information about the solar magnetic internal field if antineutrino bounds reach the 1% level and a particle physics solution to the SNP is assumed. The mechanism presented here has the advantage of being independent of the largely unknown magnetic profile of the Sun and the intrinsic neutrino magnetic moment.

hep-ph↗

arXiv1998

Finite dimensional systems with random external fields and Neutrino propagation in fluctuating media

We develop the general formalism for the study of neutrino propagation in presence of stochastic media. This formalism allows the systematic derivation of evolution equations for averaged quantities as survival probabilities and higher order distribution moments. The formalism applies equally to any finite dimensional Schroedinger equation in presence of a stochastic external force. New integro-differential equations valid for finite correlated processes are obtained for the first time. For the particular case of exponentially correlated processes a second order ordinary equation is obtained. As a consequence, the Redfield equation valid for Gaussian delta-correlated noise is rederived in a simple way. The formalism, together with the quantum correlation theorem is applied to the computation of higher moments and correlation functions of practical interest in forthcoming high precision neutrino experiments. It is shown that equal and not equal time correlators follow similar differential equations.

hep-ph↗

arXiv1998

Neutrino Spin Flavour Precession in Fluctuating Solar Magnetic Fields

The effect of a random magnetic field in the convective zone of the Sun on resonant neutrino spin oscillations, i.e. transitions of the type $ν_{eL}\to\tildeν_{μR}$, is considered. The average survival probability and the expected experimental signals in the existing solar neutrino experiments are computed as a function of the level of the noise and magnitude of a constant magnetic field in the convective zone. From comparison with observed detection rates we conclude that the RSFP solutions to the SNP with negligible mixing angle are stable under the presence of low or moderate levels of noise. Detection rates, specially in the Homestake experiment, are however sensitive to large levels of noise. As a consequence, an upper limit on small scale magnetic fluctuations is obtained from the combined solar data: $\surd\langle B^2\rangle< 140-200 $ kG for the scale $L_0\sim 1000 $ km and transition moment $μ=10^{-11} μ_B$.

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