arXiv subjects

John Ellis

Publications and source records attributed to John Ellis.

At least 433 records · Page 24Linked to original sources

arXiv1999

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

We discuss leptogenesis in the light of indications of neutrino masses and mixings from Super-Kamiokande and other data on atmospheric neutrinos, as well as the solar neutrino deficit. Neutrino masses and mixings consistent with these data may produce in a natural and generic way a lepton asymmetry that is suffient to provide the observed baryon asymmetry, after processing via non-perturbative electroweak effects. We illustrate this discussion in the framework of the string-derived flipped SU(5) model, using particle assignments and choices of vacuum parameters that are known to give realistic masses to quarks and charged leptons. We display one scenario for neutrino masses that also accommodates leptogenesis.

hep-ph↗

arXiv1999

Topological $R^4$ Inflation

We consider the possibility that higher-curvature corrections could drive inflation after the compactification to four dimensions. Assuming that the low-energy limit of the fundamental theory is eleven-dimensional supergravity to the lowest order, including curvature corrections and taking the descent from eleven dimensions to four via an intermediate five-dimensional theory, as favored by recent considerations of unification at some scale around $\sim 10^{16}$ GeV, we may obtain a simple model of inflation in four dimensions. The effective degrees of freedom are two scalar fields and the metric. The scalars arise as the large five-dimensional modulus and the self-interacting conformal mode of the metric. The effective potential has a local maximum in addition to the more usual minimum. However, the potential is quite flat at the top, and admits topological inflation. We show that the model can resolve cosmological problems and provide a mechanism for structure formation with very little fine tuning.

hep-ph↗

arXiv1998

The Glueball Filter in Central Production and Broken Scale Invariance

We propose a possible explanation of the kinematical dependence of the central production of the scalar glueball candidate observed recently by the WA91 and WA102 Collaborations, and discussed by Close and Kirk, in the context of the broken scale invariance of QCD. The dependences of glueball production on the transverse momenta and azimuthal angles of the final-state protons may be related to the structure of the trace anomaly in QCD.

hep-ph↗

arXiv1998

Five-Dimensional Gauged Supergravity and Supersymmetry Breaking in $M$~Theory

We extend the formulation of gauged supergravity in five dimensions, as obtained by compactification of $M$~theory on a deformed Calabi-Yau manifold, to include non-universal matter hypermultiplets. Even in the presence of this gauging, only the graviton supermultiplets and matter hypermultiplets can couple to supersymmetry breaking sources on the walls, though these mix with vector supermultiplets in the bulk. Whatever the source of supersymmetry breaking on the hidden wall, that on the observable wall is in general a combination of dilaton- and moduli-dominated scenarios.

hep-th↗

arXiv1998

Particle Candidates for Dark Matter

Some particle candidates for dark matter are reviewed in the light of recent experimental and theoretical developments. Models for massive neutrinos are discussed in the light of the recent atmospheric-neutrino data, and used to motivate comments on the plausibility of different solutions to the solar neutrino problem. Arguments are given that the lightest supersymmetric particle should be a neutralino χ, and accelerator and astrophysical constraints used to suggest that 50 GeV \lappeq m_χ\lappeq 600 GeV. Minimizing the fine tuning of the gauge hierarchy favours Ω_χh^2 \sim 0.1. The possibility of superheavy relic particles is mentioned, and candidates from string and $M$ theory are reviewed. Finally, the possibility of non-zero vacuum energy is discussed: its calculation is a great opportunity for a quantum theory of gravity, and the possibility that it is time dependent should not be forgotten.

astro-ph↗

arXiv1998

Beyond the Standard Model for Hillwalkers

In the first lecture, the Standard Model is reviewed, with the aim of seeing how its successes constrain possible extensions, the significance of the apparently low Higgs mass indicated by precision electroweak experiments is discussed, and defects of the Standard Model are examined. The second lecture includes a general discussion of the electroweak vacuum and an introduction to supersymmetry, motivated by the gauge hierarchy problem. In the third lecture, the phenomenology of supersymmetric models is discussed in more detail, with emphasis on the information provided by LEP data. The fourth lecture introduces Grand Unified Theories, with emphases on general principles and on neutrino masses and mixing. Finally, the last lecture contains short discussions of some further topics, including supersymmetry breaking, gauge-mediated messenger models, supergravity, strings and $M$ phenomenology.

hep-ph↗

arXiv1998

On Deep-Ocean Fe-60 as a Fossil of a Near-Earth Supernova

Live $^{60}$Fe has recently been reported in a deep-ocean ferromanganese crust. Analysis of the isotopic ratios in the sample suggests that the measured $^{60}$Fe abundance exceeds the levels generated by terrestrial and cosmogenic sources, and it has been proposed that the excess of $^{60}$Fe is a signature of a supernova that exploded near the earth several Myr ago. In this paper, we consider the possible background sources, and confirm that the measured $^{60}$Fe is significantly higher than all known backgrounds, in contrast with the reported abundance of live $^{53}$Mn. We discuss scenarios in which the data are consistent with a supernova event at a distance $D \sim 30$ pc and an epoch $t_{\rm SN} \sim 5$ Myr ago. We propose tests that could confirm or refute the interpretation of the $^{60}$Fe discovery, including searches for $^{10}$Be, $^{129}$I and $^{146}$Sm. Such a nearby supernova event might have had some impact on the earth's biosphere, principally by enhancing the cosmic-ray flux. This might have damaged the earth's ozone layer, enhancing the penetration of solar ultraviolet radiation. In this connection, we comment on the Middle Miocene and Pliocene mini-extinction events. We also speculate on the possibility of a supernova-induced "cosmic-ray winter," if cosmic rays play a significant role in seeding cloud formation.

astro-ph↗

arXiv1998

Cosmological Fine Tuning, Supersymmetry, and the Gauge Heirarchy Problem

We study the extent to which the cosmological fine-tuning problem - why the relic density of neutralino cold dark matter particles $χ$ is similar to that of baryons - is related to the fine-tuning aspect of the gauge hierarchy problem - how one arranges that M_W << M_P without unnatural choices of MSSM parameters. Working in the minimal supergravity framework with universal soft supersymmetry-breaking parameters as inputs, we find that the hierarchical fine tuning is minimized for Ω_χ h^2 \sim 0.1. Conversely, imposing Ω_χ h^2 < 1 does not require small hierarchical fine tuning, but the exceptions to this rule are rather special, with parameters chosen such that m_χ\sim M_Z/2 or M_h/2, or else m_χ \simgt m_t. In the first two cases, neutralino annihilation receives a large contribution from a direct-channel pole, whereas in the third case it is enhanced by the large top Yukawa coupling.

hep-ph↗

arXiv1998

Five-Dimensional Aspects of M-Theory Dynamics and Supersymmetry Breaking

We discuss the reduction of the eleven-dimensional M-theory effective Lagrangian, considering first compactification from eleven to five dimensions on a Calabi-Yau manifold, followed by reduction to four dimensions on an S_1/Z_2 line segment at a larger distance scale. The Calabi-Yau geometry leads to a structure of the five-dimensional Lagrangian that has more freedom than the eleven-dimensional theory. In five dimensions one obtains a non-linear sigma-model coupled to gravity, which implies non-trivial dynamics for the scalar moduli fields in the bulk of the Z_2 orbifold. We discuss solutions to the five-dimensional equations of motion in the presence of sources localized on the boundaries of the Z_2 orbifold that may trigger supersymmetry breaking, e.g., gaugino condensates. The transmission of supersymmetry breaking from the hidden wall to the visible wall is demonstrated in specific models. The role of the messenger of supersymmetry breaking may be played by the gravity supermultiplet and/or by scalar hypermultiplets. The latter include the universal hypermultiplet associated with the Calabi-Yau volume, and also the hypermultiplets associated with deformations of its complex structure, which mix in general.

hep-ph↗

arXiv1998

Sensitivity of Astrophysical Observations to Gravity-Induced Wave Dispersion in Vacuo

We discuss possible signatures of quantum gravity for the propagation of light, including an energy-dependent velocity (refractive index), dispersion in velocity at a given energy, and birefringence. We also compare the sensitivities of different astrophysical observations, including BATSE data on GRB 920229, BeppoSAX data on GRB 980425, the possible HEGRA observation of GRB 920925c, and Whipple observations of the active galaxy Mrk 421. Finally, we discuss the prospective sensitivities of AMS and GLAST.

astro-ph↗

arXiv1998

Time-Dependent Vacuum Energy Induced by D-Particle Recoil

We consider cosmology in the framework of a `material reference system' of D particles, including the effects of quantum recoil induced by closed-string probe particles. We find a time-dependent contribution to the cosmological vacuum energy, which relaxes to zero as $\sim 1/ t^2$ for large times $t$. If this energy density is dominant, the Universe expands with a scale factor $R(t) \sim t^2$. We show that this possibility is compatible with recent observational constraints from high-redshift supernovae, and may also respect other phenomenological bounds on time variation in the vacuum energy imposed by early cosmology.

gr-qc↗

arXiv1998

Neutralino-Stau Coannihilation and the Cosmological Upper Limit on the Mass of the Lightest Supersymmetric Particle

We consider the effects of neutralino-stau coannihilations on the cosmological relic density of the lightest supersymmetric particle (LSP) $χ$ in the minimal supersymmetric extension of the Standard Model (MSSM), particularly in the constrained MSSM in which universal supergravity inputs at the GUT scale are assumed. For much of the parameter space in these models, $χ$ is approximately a U(1) gaugino ${\tilde B}$, and constraints on the cosmological relic density $Ω_{\tilde B} h^2$ yield an upper bound on the bino mass. We show that in regions of parameter space for which the cosmological bound is nearly saturated, coannihilations of the $\tilde B$ with the stau, the next lightest sparticle, are important and may reduce significantly the bino relic density. Including also bino coannihilations with the selectrons and smuons, we find that the upper limit on $m_χ$ is increased from about 200 GeV to about 600 GeV in the constrained MSSM, with a similar new upper limit expected in the MSSM.

hep-ph↗

arXiv1998

Charginos and Neutralinos in the Light of Radiative Corrections: Sealing the Fate of Higgsino Dark Matter

We analyze the LEP constraints from searches for charginos $χ^{\pm}$ and neutralinos $χ_i$, taking into account radiative corrections to the relations between their masses and the underlying Higgs-mixing and gaugino-mass parameters $μ, m_{1/2}$ and the trilinear mass parameter $A_t$. Whilst radiative corrections do not alter the excluded domain in $m_{χ^{\pm}}$ as a function of $m_{χ^{\pm}} - m_χ$, its mapping into the $μ, m_{1/2}$ plane is altered. We update our previous lower limits on the mass of gaugino dark matter and on tan$β$, the ratio of Higgs vacuum expectation values, in the light of the latest LEP data and these radiative corrections. We also discuss the viability of Higgsino dark matter, incorporating co-annihilation effects into the calculation of the Higgsino relic abundance. We find that Higgsino dark matter is viable for only a very limited range of $μ$ and $m_{1/2}$, which will be explored completely by upcoming LEP runs.

hep-ph↗

arXiv1998

Confinement in Gauge Theories from the Condensation of World-Sheet Defects in Liouville String

We present a Liouville-string approach to confinement in four-dimensional gauge theories, which extends previous approaches to include non-conformal theories. We consider Liouville field theory on world sheets whose boundaries are the Wilson loops of gauge theory, which exhibit vortex and spike defects. We show that world-sheet vortex condensation occurs when the Wilson loop is embedded in four target space-time dimensions, and show that this corresponds to the condensation of gauge magnetic monopoles in target space. We also show that vortex condensation generates a effective string tension corresponding to the confinement of electric degrees of freedom. The tension is independent of the string length in a gauge theory whose electric coupling varies logarithmically with the length scale. The Liouville field is naturally interpreted as an extra target dimension, with an anti-de-Sitter (AdS) structure induced by recoil effects on the gauge monopoles, interpreted as D branes of the effective string theory. Black holes in the bulk AdS space correspond to world-sheet defects, so that phases of the bulk gravitational system correspond to the different world-sheet phases, and hence to different phases of the four-dimensional gauge theory. Deconfinement is associated with a Berezinskii-Kosterlitz-Thouless transition of vortices on the Wilson-loop world sheet, corresponding in turn to a phase transition of the black holes in the bulk AdS space.

hep-th↗

arXiv1998

High-Energy QCD as a Topological Field Theory

We propose an identification of the conformal field theory underlying Lipatov's spin-chain model of high-energy scattering in perturbative QCD. It is a twisted N=2 supersymmetric topological field theory, which arises as the limiting case of the SL(2,R)/U(1) non-linear sigma model that also plays a role in describing the Quantum Hall effect and black holes in string theory. The doubly-infinite set of non-trivial integrals of motion of the high-energy spin-chain model displayed by Faddeev and Korchemsky are identified as the Cartan subalgebra of a W_{\infty} \otimes W_{\infty} bosonic sub-symmetry possessed by this topological theory. The renormalization group and an analysis of instanton perturbations yield some understanding why this particular topological spin-chain model emerges in the high-energy limit, and provide a new estimate of the asymptotic behaviour of multi-Reggeized-gluon exchange.

hep-ph↗

arXiv1998

Summary of DIS 98

A personal selection is made of some of the hot topics debated at this conference, including examples of using our knowledge of QCD to make electroweak measurements, structure functions at low x in the light of the corrections to the leading BFKL behaviour recently calculated, diffraction, the existence of one or more Pomerons and whether it/they may have a well-defined structure function, some issues in hadronic final states and polarized structure functions, and the interesting events at large Q^2 and x and with isolated leptons and missing transverse energy. Finally, some of the prospects for future deep-inelastic scattering facilities are reviewed, and the interested community is encouraged to organize itself to advocate their approval.

hep-ph↗

arXiv1998

A Microscopic Liouville Arrow of Time

We discuss the treatment of quantum-gravitational fluctuations in the space-time background as an `environment', using the formalism for open quantum-mechanical systems, which leads to a microscopic arrow of time. After reviewing briefly the open-system formalism, and the motivations for treating quantum gravity as an `environment', we present an example from general relativity and a general framework based on non-critical strings, with a Liouville field that we identify with time. We illustrate this approach with calculations in the contexts of two-dimensional models and $D$ branes. Finally, some prospects for observational tests of these ideas are mentioned.

hep-th↗

arXiv1998

Aspects of M Theory and Phenomenology

A brief review is presented of selected topics, including a world-sheet formulation of M theory, couplings and scales in M phenomenology, the perils of baryon decay and the possible elevation of free-fermion models to true M- or F-theory compactifications.

hep-ph↗