arXiv subjects

J. W. F. Valle

Publications and source records attributed to J. W. F. Valle.

At least 253 records · Page 14Linked to original sources

arXiv1996

Signatures of Spontaneous Breaking of R-Parity in Gluino Cascade Decays at LHC

We study the pattern of gluino cascade decays in a class of supersymmetric models where R-parity is spontaneously broken. We give a detailed discussion of the R-parity violating decays of the lightest neutralino, the second lightest neutralino and the lightest chargino. The multi-lepton and same-sign dilepton signal rates expected in these models are compared with those predicted in the Minimal Supersymmetric Standard Model. We show that these rates can be substantially enhanced in broken R-parity models.

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arXiv1996

Single-Photon Z Decays and Small Neutrino Masses

We discuss some rare Z decay signatures associated with extensions of the Standard Model with spontaneous lepton number violation at the electroweak scale. We show that single-photon Z decays such as $Z \to γH$ and $Z \to γJ J$ where H is a CP-even Higgs boson and J denotes the associated CP-odd Majoron may occur with branching ratios accessible to LEP sensitivities, even though the corresponding neutrino masses can be very small, as required in order to explain the deficit of solar neutrinos.

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arXiv1996

The MSW conversion of solar neutrinos and random matter density perturbations

We present a generalization of the resonant neutrino conversion in matter, including a random component in the matter density profile. The study is focused on the effect of such matter perturbations upon both large and small mixing angle MSW solutions to the solar neutrino problem. This is carried out both for the active-active $ν_e \to ν_{μ,τ}$ as well as active-sterile $ν_e \to ν_s$ conversion channels. We find that the small mixing MSW solution is much more stable (especially in $δm^2$) than the large mixing solution. Future solar neutrino experiments, such as Borexino, could probe solar matter density noise at the few percent level.

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arXiv1996

Gravitational Violation of R Parity and its Cosmological Signatures

The discrete R-parity ($R_P$) usually imposed on the Supersymmetric (SUSY) models is expected to be broken at least gravitationally. If the neutralino is a dark matter particle its decay channels into positrons, antiprotons and neutrinos are severely constrained from astrophysical observations. These constraints are shown to be violated even for Planck-mass-suppressed dimension-five interactions arising from gravitational effects. We perform a general analysis of gravitationally induced $R_P$ violation and identify two plausible and astrophysically consistent scenarios for achieving the required suppression.

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arXiv1996

Supersymmetric Unification with Radiative Breaking of R-parity

We show how R-parity can break spontaneously as a result of radiative corrections in unified N=1 supergravity models. We illustrate this with a concrete rank-four unified model, where the spontaneous breaking of R-parity is accompanied by the existence of a physical majoron. We determine the resulting supersymmetric particle mass spectrum and show that R-parity-breaking signals may be detectable at LEP200.

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arXiv1996

Erratum for "Nucleosynthesis Constraints on Active-Sterile..."

The magnetization asymmetry given in eq. 3.6 of the above paper (ref. [1], hep-ph/9402332) has a wrong relative sign between particle and anti-particle contributions. Here we present the derivation of the correct sign and its implications for the limits derived in [1]. This sign has also been recently derived in a paper by Elmfors, Grasso and Raffelt, CERN-TH/96-88 [hep-ph/9605250] (ref. [2]) using a different method. While the sign error in [1] does affect the nucleosynthesis bounds derived in [1], we would like to stress that, in contrast to the criticism made in [2], it does not affect in any way the conclusions reached in subsequent papers in S. Pastor, V. B. Semikoz, J. W. F. Valle, Phys.Lett.B369 (1996) 301 and Astropart. Phys. 3 (1995) 87.

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arXiv1996

Supernova Bounds on Supersymmetric $R$-parity Violating Interactions

We re-examine resonant massless-neutrino conversions in a dense medium induced by flavour changing neutral current (FCNC) interactions. We show how the observed $\barν_e$ energy spectra from SN1987a and the supernova $r$-process nucleosynthesis provide constraints on supersymmetric models with $R$ parity violation, which are much more stringent than those obtained from the laboratory. We also suggest that resonant massless-neutrino conversions may play a positive role in supernova shock reheating. Finally, we examine the constraints on explicit $R$-parity-violating FCNCs in the presence of non-zero neutrino masses in the eV range, as indicated by present hot dark matter observations.

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arXiv1996

New Signatures for a Light Stop at LEP2 in SUSY Models with Spontaneously Broken R-Parity

In a class of supersymmetric models with R-parity breaking the lightest stop can have new decay modes into third generation fermions, $\tilde{t}_1 \rightarrow b + τ$. We show that this decay may be dominant or at least comparable to the ordinary R-parity conserving mode $\tilde{t}_1 \rightarrow c + \tildeχ_1^0$, where $\tildeχ_1^0$ denotes the lightest neutralino. The new R-parity violating decay mode could provide new signatures for stop production at LEP.

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arXiv1996

Resonant Conversion of Massless Neutrinos in Supernovae

It has been noted for a long time that, in some circumstances, {\sl massless} neutrinos may be {\sl mixed} in the leptonic charged current. Conventional neutrino oscillation searches in vacuum are insensitive to this mixing. We discuss the effects of resonant massless-neutrino conversions in the dense medium of a supernova. In particular, we show how the detected $\barν_e$ energy spectra from SN1987a and the supernova $r$-process nucleosynthesis may be used to provide very stringent constraints on the mixing of {\sl massless} neutrinos.

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arXiv1996

LEP Sensitivities to Spontaneous R-Parity Violating Signals

We illustrate the sensitivities of LEP experiments to leptonic signals associated to models where supersymmetry (SUSY) is realized with spontaneous breaking of R-parity. We focus on missing transverse momentum plus acoplanar muon events arising from lightest neutralino single production $χν$ as well as pair production $χχ$, followed by $χ$ decays, where $χ$ denotes the lightest neutralino. We show that the integrated luminosity achieved at LEP already starts probing the basic parameters of the theory. We discuss the significance of these constraints for the simplest spontaneous R-parity breaking models and their relevance for future searches of SUSY particles.

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arXiv1996

Physics Beyond the Standard Model

We discuss some of the signatures associated with extensions of the Standard Model related to the neutrino and electroweak symmetry breaking sectors, with and without supersymmetry. The topics include a basic discussion of the theory of neutrino mass and the corresponding extensions of the Standard Model that incorporate massive neutrinos; an overview of the present observational status of neutrino mass searches, with emphasis on solar neutrinos, as well the as cosmological data on the amplitude of primordial density fluctuations; the implications of neutrino mass in cosmological nucleosynthesis, non-accelerator, as well as in high energy particle collider experiments. Turning to the electroweak breaking sector, we discuss the physics potential for Higgs boson searches at LEP200, including Majoron extensions of the Standard Model, and the physics of invisibly decaying Higgs bosons. We discuss the minimal supersymmetric Standard Model phenomenology, as well as some of the laboratory signatures that would be associated to models with R parity violation, especially in Z and scalar boson decays.

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arXiv1996

Neutrino Properties

A brief sketch is made of the present observational status of neutrino properties, with emphasis on the hints from solar and atmospheric neutrinos, as well as cosmological data on the amplitude of primordial density fluctuations. Implications of neutrino mass in particle accelerators, astrophysics and cosmology are discussed.

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arXiv1996

The effect of random matter density perturbations on the MSW solution to the solar neutrino problem

We consider the implications of solar matter density random noise upon resonant neutrino conversion. The evolution equation describing MSW-like conversion is derived in the framework of the Schrödinger approach. We study quantitatively their effect upon both large and small mixing angle MSW solutions to the solar neutrino problem. This is carried out both for the active-active $ν_e \ra ν_{μ,τ}$ as well as active-sterile $ν_e \ra ν_s$ conversion channels. We find that the small mixing MSW solution is much more stable (especially in $Δm^2$) than the large mixing solution. The possible existence of solar matter density noise at the few percent level could be tested at future solar neutrino experiments, especially Borexino.

hep-ph↗

arXiv1996

Higgs Physics at LEP2

In this report we review the prospects for Higgs physics at LEP2. The theoretical aspects and the phenomenology of Higgs particles are discussed within the Standard Model (SM) and the Minimal Supersymmetric Standard Model (MSSM). The experimental search techniques are described and the discovery limits for Higgs bosons in the LEP2 energy range are summarized. In addition, opportunities of detecting Higgs particles in non-minimal extensions of the SM and the MSSM are investigated.

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arXiv1996

An improved cosmological bound on the tau-neutrino mass

We consider the influence of non-equilibrium electronic neutrinos (and anti-neutrinos) on the neutron-to-proton ratio. These neutrinos would come from massive $ν_τ$ annihilations $\bar ν_τν_τ\rightarrow \bar ν_e ν_e$. For sufficiently large $ν_τ$ masses this new effect would strongly enhance the (n/p)-ratio, leading to a very stringent bound on the $ν_τ$ mass, even adopting a rather weak upper bound on the effective number on neutrino species during nucleosynthesis.

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arXiv1996

A Flipped SO(10) GUT Model and the Fermion Mass Hierarchy

We present a viable flipped version of the SO(10) model consistent with the phenomenological requirements of having a non-trivial quark mixing matrix, natural doublet-triplet splitting, and a single pair of light electroweak Higgs doublet scalar bosons. In the presence of suitable non-renormalizable superpotential terms the model can reproduce the hierarchy observed in quark masses and mixings as well as an acceptable neutrino mass generated via the seesaw mechanism needed to explain dark matter and solar neutrino data.

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arXiv1996

Searching for Invisibly Decaying Higgs Bosons at LEP II

We study the potential of LEP II to unravel the existence of invisibly decaying Higgs bosons, predicted in a wide class of models. We perform a model independent analysis, focusing our attention to the final state topologies exhibiting $b \bar{b}$ or $\ell^+ \ell^-$ ($\ell=μ$ or $e$) pairs and missing energy. We carefully evaluate the signals and backgrounds, choosing appropriate cuts to enhance the discovery limits. Our results demonstrate that LEP II is capable of discovering such a Higgs boson for a wide range of masses and couplings.

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arXiv1995

A New Type of Resonant Neutrino Conversions Induced by Magnetic Fields

We consider resonant neutrino conversions in magnetised matter, such as a degenerate electron gas. We show how magnetisation effects caused by axial vector interactions of neutrinos with the charged leptons in the medium can induce a new type of resonant neutrino conversion which may occur even in situations where the MSW effect does not occur, such as the case of degenerate or inverted neutrino mass spectra. Our new resonance may simultaneously affect anti-neutrino $\bar{ν_a} \leftrightarrow \barν_b$ as well as neutrino $ν_{a} \leftrightarrow ν_b$ flavour conversions, and therefore it may substantially affect supernova neutrino energy spectra. Using SN1987A data we conclude that only laboratory experiments with long baseline such as ICARUS or MINOS are likely to find neutrino oscillations due to their sensitivity to small $Δm^2$. We also comment on the possibility of resonant conversions induced by Majorana neutrino transition moments and mention the case of sterile neutrinos $ν_s$.

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