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J. Ellis

Publications and source records attributed to J. Ellis.

At least 127 records · Page 7Linked to original sources
arXiv2000

Calculations of Neutralino-Stau Coannihilation Channels and the Cosmologically Relevant Region of MSSM Parameter Space

Assuming that the lightest supersymmetric particle (LSP) is the lightest neutralino, we present a detailed exploration of neutralino-stau coannihilation channels, including analytical expressions and numerical results. We also include neutralino coannihilations with the selectron and smuon. We evaluate the implications of coannihilations for the cosmological relic density of the LSP, which is assumed to be stable, in the constrained minimal supersymmetric extension of the Standard Model (CMSSM), in which the soft supersymmetry-breaking parameters are universal at the supergravity GUT scale. We evaluate the changes due to coannihilations in the region of the MSSM parameter space that is consistent with the cosmological upper limit on the relic LSP density. In particular, we find that the upper limit on the mass of the neutralino is increased from about 200 GeV to about 600 GeV in the CMSSM, and estimate a qualitatively similar increase for gauginos in the general MSSM.

hep-ph↗
arXiv2000

Charged-Lepton-Flavour Violation in Kaon Decays in Supersymmetric Theories

We discuss rare kaon decays that violate charged-lepton flavour conservation in supersymmetric theories with and without R parity, in view of possible experiments using an intense proton source as envisaged for a neutrino factory. In the Minimal Supersymmetric Standard Model, such decays are generated by box diagrams involving charginos and neutralinos, but the limits from μ-> e γ, μ-e conversion and Δm_K constrain the branching ratios to challengingly small values. However, this is no longer the case in R-violating theories, where such decays may occur at tree level at rates close to the present experimental limits. Within this framework, we obtain bounds on products of LL\bar{E} and LQ\bar{D} operators from the experimental upper limits on K^0 -> μ^\pm e^\mp and K^{\pm,0} -> π^{\pm,0} μ^\pm e^\mp decays. We also note the possibility of like-sign lepton decays K^\pm -> π^\mp \ell^\pm \ell^\pm in the presence of non-zero \tilde{b}_L-\tilde{b}_R mixing. We conclude that rare kaon decays violating charged-lepton flavour conservation could be an interesting signature of R violation.

hep-ph↗
arXiv2000

Results from an Algebraic Classification of Calabi-Yau Manifolds

We present results from an inductive algebraic approach to the systematic construction and classification of the `lowest-level' CY3 spaces defined as zeroes of polynomial loci associated with reflexive polyhedra, derived from suitable vectors in complex projective spaces. These CY3 spaces may be sorted into `chains' obtained by combining lower-dimensional projective vectors classified previously. We analyze all the 4242 (259, 6, 1) two- (three-, four-, five-) vector chains, which have, respectively, K3 (elliptic, line-segment, trivial) sections, yielding 174767 (an additional 6189, 1582, 199) distinct projective vectors that define reflexive polyhedra and thereby CY3 spaces, for a total of 182737. These CY3 spaces span 10827 (a total of 10882) distinct pairs of Hodge numbers h_11, h_12. Among these, we list explicitly a total of 212 projective vectors defining three-generation CY3 spaces with K3 sections, whose characteristics we provide.

hep-th↗
arXiv2000

Towards an Algebraic Classification of Calabi-Yau Manifolds I: Study of K3 Spaces

We present an inductive algebraic approach to the systematic construction and classification of generalized Calabi-Yau (CY) manifolds in different numbers of complex dimensions, based on Batyrev's formulation of CY manifolds as toric varieties in weighted complex projective spaces associated with reflexive polyhedra. We show how the allowed weight vectors in lower dimensions may be extended to higher dimensions, emphasizing the roles of projection and intersection in their dual description, and the natural appearance of Cartan-Lie algebra structures. The 50 allowed extended four-dimensional vectors may be combined in pairs (triples) to form 22 (4) chains containing 90 (91) K3 spaces, of which 94 are distinct, and one further K3 space is found using duality. In the case of CY_3 spaces, pairs (triples) of the 10~270 allowed extended vectors yield 4242 (259) chains with K3 (elliptic) fibers containing 730 additional K3 polyhedra. A more complete study of CY_3 spaces is left for later work.

hep-th↗
arXiv1999

Gravitational-Recoil Effects on Fermion Propagation in Space-Time Foam

Motivated by the possible experimental opportunities to test quantum gravity via its effects on high-energy neutrinos propagating through space-time foam, we discuss how to incorporate spin structures in our D-brane description of gravitational recoil effects in vacuo. We also point to an interesting analogous condensed-matter system. We use a suitable supersymmetrization of the Born-Infeld action for excited D-brane gravitational backgrounds to argue that energetic fermions may travel slower than the low-energy velocity of light: δc / c \sim -E/M. It has been suggested that Gamma-Ray Bursters may emit pulses of neutrinos at energies approaching 10^{19} eV: these would be observable only if M \gsim 10^{27} GeV.

gr-qc↗
arXiv1999

Scalar Glueball--Quarkonium Mixing and the Structure of the QCD Vacuum

We use Ward identities of broken scale invariance to infer the amount of scalar glueball--$\bar{q}q$ meson mixing from the ratio of quark and gluon condensates in the QCD vacuum. Assuming dominance by a single scalar state, as suggested by a phase-shift analysis, we find a mixing angle $γ\sim 36^{\circ}$, corresponding to near-maximal mixing of the glueball and $\bar{s}s$ components.

hep-ph↗
arXiv1999

Hadronic Probes of the Polarized Intrinsic Strangeness of the Nucleon

We have previously interpreted the various large apparent violations of the naive Okubo-Zweig-Iizuka (OZI) rule found in many channels in $\bar{p}p$ annihilation at LEAR as evidence for an intrinsic polarized $\bar{s}s$ component of the nucleon wave function. The model is further supported by new data from LEAR and elsewhere. Here we discuss in more detail the possible form of the $\bar{s}s$ component of the nucleon wave function, interpret the new data and clarify the relative roles of strangeness shake-out and rearrangement, discuss whether alternative interpretations are still allowed by the new data, and propose more tests of the model.

hep-ph↗
arXiv1999

Astrophysical Probes of the Constancy of the Velocity of Light

We discuss possible tests of the constancy of the velocity of light using distant astrophysical sources such as gamma-ray bursters (GRBs), Active Galactic Nuclei (AGNs) and pulsars. This speculative quest may be motivated by some models of quantum fluctuations in the space-time background, and we discuss explicitly how an energy-dependent variation in photon velocity δc/ c \sim - E / M arises in one particular quantum-gravitational model. We then discuss how data on GRBs may be used to set limits on variations in the velocity of light, which we illustrate using BATSE and OSSE observations of the GRBs that have recently been identified optically and for which precise redshifts are available. We show how a regression analysis can be performed to look for an energy-dependent effect that should correlate with redshift. The present data yield a limit M \gsim 10^{15} GeV for the quantum gravity scale. We discuss the prospects for improving this analysis using future data, and how one might hope to distinguish any positive signal from astrophysical effects associated with the sources.

astro-ph↗
arXiv1999

Neutrino Masses, Mixing Angles and the Unification of Couplings in the MSSM

In the light of the gathering evidence for $ν_μ-ν_τ$ neutrino oscillations, coming in particular from the Super-Kamiokande data on atmospheric neutrinos, we re-analyze the unification of gauge and Yukawa couplings within the minimal supersymmetric extension of the Standard Model (MSSM). Guided by a range of different grand-unified models, we stress the relevance of large mixing in the lepton sector for the question of bottom-tau Yukawa coupling unification. We also discuss the dependence of the favoured value of $\tanβ$ on the characteristics of the high-energy quark and lepton mass matrices. In particular, we find that, in the presence of large lepton mixing, Yukawa unification can be achieved for intermediate values of $\tanβ$ that were previously disfavoured. The renormalization-group sensitivity to the structures of different mass matrices may enable Yukawa unification to serve as a useful probe of GUT models.

hep-ph↗
arXiv1999

Tests of the Equivalence Principle with Neutral Kaons

We test the Principle of Equivalence for particles and antiparticles, using CPLEAR data on tagged K0 and K0bar decays into pi^+ pi^-. For the first time, we search for possible annual, monthly and diurnal modulations of the observables |eta_{+-}| and phi_{+-}, that could be correlated with variations in astrophysical potentials. Within the accuracy of CPLEAR, the measured values of |eta_{+-}| and phi_{+-} are found not to be correlated with changes of the gravitational potential. We analyze data assuming effective scalar, vector and tensor interactions, and we conclude that the Principle of Equivalence between particles and antiparticles holds to a level of 6.5, 4.3 and 1.8 x 10^{-9}, respectively, for scalar, vector and tensor potentials originating from the Sun with a range much greater than the distance Earth-Sun. We also study energy-dependent effects that might arise from vector or tensor interactions. Finally, we compile upper limits on the gravitational coupling difference between K0 and K0bar as a function of the scalar, vector and tensor interaction range.

hep-ex↗
arXiv1998

Probing the Structure of the Pomeron

We suggest that the pseudo-rapidity cut dependence of diffractive deep-inelastic scattering events at HERA may provide a sensitive test of models of diffraction. A comparison with the experimental cross section shows that the Donnachie-Landshoff model and a simple two-gluon exchange model of the pomeron model are disfavoured. However a model with a direct coupling of the pomeron to quarks is viable for a harder quark--pomeron form factor, as is a model based on the leading-twist operator contribution. We also consider a direct-coupling scalar pomeron model. We comment on the implications of these results for the determination of the partonic structure of the pomeron.

hep-ph↗
arXiv1998

Bose-Einstein Correlations in a Space-Time Approach to e+ e- Annihilation into Hadrons

A new treatment of Bose-Einstein correlations is incorporated in a space-time parton-shower model for e+ e- annihilation into hadrons. Two alternative afterburners are discussed, and we use a simple calculable model to demonstrate that they reproduce successfully the size of the hadron emission region. One of the afterburners is used to calculate two-pion correlations in e+ e- -> Z^0 -> hadrons and e+ e- -> W+ W- -> hadrons. Results are shown with and without resonance decays, for correlations along and transverse to the thrust jet axis in these two classes of events.

hep-ph↗
arXiv1998

Haggling over the fine-tuning price

We amplify previous discussions of the fine-tuning price to be paid by supersymmetric models in the light of LEP data, especially the lower bound on the Higgs boson mass, studying in particular its power of discrimination between different parameter regions and different theoretical assumptions. The analysis is performed using the full one-loop effective potential. The whole range of $\tanβ$ is discussed, including large values. In the minimal supergravity model with universal gaugino and scalar masses, a small fine-tuning price is possible only for intermediate values of $\tanβ$. However, the fine-tuning price in this region is significantly higher if we require $b-τ$ Yukawa-coupling unification. On the other hand, price reductions are obtained if some theoretical relation between MSSM parameters is assumed, in particular between $μ_0$, $M_{1/2}$ and $A_0$. Significant price reductions are obtained for large $\tanβ$ if non-universal soft Higgs mass parameters are allowed. Nevertheless, in all these cases, the requirement of small fine tuning remains an important constraint on the superpartner spectrum. We also study input relations between MSSM parameters suggested in some interpretations of string theory: the price may depend significantly on these inputs, potentially providing guidance for building string models. However, in the available models the fine-tuning price may not be reduced significantly.

hep-ph↗
arXiv1998

Neutrino Textures in the Light of Super-Kamiokande Data and a Realistic String Model

Motivated by the Super-Kamiokande atmospheric neutrino data, we discuss possible textures for Majorana and Dirac neutrino masses within the see-saw framework. The main purposes of this paper are twofold: first to obtain intuition from a purely phenomenological analysis, and secondly to explore to what extent it may be realized in a specific model. We comment initially on the simplified two-generation case, emphasizing that large mixing is not incompatible with a large hierarchy of mass eigenvalues. We also emphasize that renormalization-group effects may amplify neutrino mixing, presenting semi-analytic expressions for estimating this amplification. Several examples are then given of three-family neutrino mass textures which may also accommodate the persistent solar neutrino deficit, with different assumptions for the neutrino Dirac mass matrices. We comment on a few features of neutrino mass textures arising in models with a U(1) flavour symmetry. Finally, we discuss the possible pattern of neutrino masses in a `realistic' flipped SU(5) model derived from string theory, illustrating how a desirable pattern of mixing may emerge. Both small- or large-angle MSW solutions are possible, whilst a hierarchy of neutrino masses appears more natural than near-degeneracy. This model contains some unanticipated features that may also be relevant in other models: the neutrino Dirac matrices may not be related closely to the quark mass matrices, and the heavy Majorana states may include extra gauge-singlet fields.

hep-ph↗
arXiv1998

An Analysis of Diffraction in Deep-Inelastic Scattering

We propose a simple parametrization for the deep-inelastic diffractive cross section. It contains the contribution of $q\bar{q}$ production to both the longitudinal and the transverse diffractive structure functions, and of the production of $q\bar{q}g$ final states from transverse photons. We start from the hard region and perform a suitable extrapolation into the soft region. We test our model on the 1994 ZEUS and H1 data, and confront it with the H1 conjecture of a singular gluon distribution.

hep-ph↗
arXiv1997

The fine-tuning price of LEP

We quantify the amount of fine tuning of input parameters of the Minimal Supersymmetric Extension of the Standard Model (MSSM) that is needed to respect the lower limits on sparticle and Higgs masses imposed by precision electroweak measurements at LEP, measurements of $b\to X_sγ$, and searches at LEP 2. If universal input scalar masses are assumed in a gravity-mediated scenario, a factor of $\gappeq180$ is required at $\tanβ\sim1.65$, decreasing to $\sim20$ at $\tanβ\sim10$. The amount of fine tuning is not greatly reduced if non-universal input scalar Higgs masses are allowed, but may be significantly reduced if some theoretical relations between MSSM parameters are assumed.

hep-ph↗
arXiv1997

Fermion Mass Textures in an M-Inspired Flipped SU(5) Model Derived from String

We are inspired by the facts that M-theory may reconcile the supersymmetric GUT scale with that of quantum gravity, and that it provides new avenues for low-energy supersymmetry breaking, to re-examine a flipped SU(5) model that has been derived from string and may possess an elevation to a fully-fledged M-phenomenological model. Using a complete analysis of all superpotential terms through the sixth order, we explore in this model a new flat potential direction that provides a pair of light Higgs doublets, yields realistic textures for the fermion mass matrices, and is free of R-violating interactions and dimension-five proton decay operators.

hep-ph↗