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J. Ellis

Publications and source records attributed to J. Ellis.

At least 163 records · Page 9Linked to original sources
arXiv1995

Lowering alpha_s by flipping SU(5)

We show that the prediction for $α_s(M_Z)$ in flipped SU(5) is naturally lower than in minimal SU(5), and that the former can accommodate the full range of $α_s(M_Z)$ presently allowed by experiment. Our computations include two-loop ($δ_{\rm 2loop}$) and light ($δ_{\rm light}$) and heavy ($δ_{\rm heavy}$) threshold effects. Unlike minimal SU(5), in flipped SU(5) the heavy threshold effects can naturally decrease the predicted value of $α_s(M_Z)$. We also show that the value of the proton lifetime into the dominant channel $p\to e^+π^0$ is within the observable range at SuperKamiokande, and should discriminate against minimal supersymmetric SU(5), where the dominant mode is $p\to\barνK^+$.

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arXiv1995

Neutralino dark matter in supersymmetric models with non--universal scalar mass terms

Neutralino dark matter is studied in the context of a supergravity scheme where the scalar mass terms are not constrained by universality conditions at the grand unification scale. We analyse in detail the consequences of the relaxation of this universality assumption on the supersymmetric parameter space, on the neutralino relic abundance and on the event rate for the direct detection of relic neutralinos.

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arXiv1995

Search for Large Rapidity Gap Events in e^+ e^- Annihilation

We investigate the cross-section for the production of a low-mass colour-singlet cluster in $e^+e^-$ annihilation with a large rapidity gap between the colour-singlet cluster and the other jets. It is argued that such events are the cross-channel analogue of large-rapidity-gap events in deep-inelastic scattering, and therefore could in principle be used to investigate the analytic continuation of the BFKL pomeron to the positive-$t$ kinematic regime, where one would expect the trajectory to pass through glueball states. The cross section can be calculated in perturbative QCD, so that the infrared scale arising from non-perturbative effects, which prevents an exponential fall-off with rapidity gap in the case of deep-inelastic scattering, is absent in $e^+ e^-$ annihilation. Correspondingly, the cross section for such events decreases rapidly with increasing rapidity gap.

hep-ph↗
arXiv1995

Precision Tests of CPT Symmetry and Quantum Mechanics in the Neutral Kaon System

We present a systematic phenomenological analysis of the tests of CPT symmetry that are possible within an {\em open} quantum-mechanical description of the neutral kaon system that is motivated by arguments based on quantum gravity and string theory. We develop a perturbative expansion in terms of the three small CPT-violating parameters admitted in this description, and provide expressions for a complete set of $K \rightarrow 2π, 3π$ and $π\ellν$ decay observables to second order in these small parameters. We also illustrate the new tests of CPT symmetry and quantum mechanics that are possible in this formalism using a regenerator. Indications are that experimental data from the CPLEAR and previous experiments could be used to establish upper bounds on the CPT-violating parameters that are of order $10^{-19}$ GeV, approaching the order of magnitude that may be attainable in quantum theories of gravity.

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arXiv1995

A string scenario for inflationary cosmology

We describe a scenario for inflation in the framework of non-critical string theory, which does not employ an inflaton field. There is an exponential expansion of the volume of the Universe, induced by enormous entropy production in the early stages of cosmological evolution. This is associated with the loss of information carried by global string modes that cross the particle horizon. It is the same loss of information that induces irreversible time flow when target time is identified with the world-sheet Liouville mode. The resulting scenario for inflation is described by a string analogue of the Fokker-Planck equation that incorporates diffusion and dissipative effects. Cosmological density perturbations are naturally small.

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arXiv1995

THE PROTON SPIN PUZZLE AND DEPOLARIZATION IN $\bar{p}p\to\barΛΛ$

We point out that the measurement of target spin depolarization $D_{nn}$ in the $\bar{p}p\to\barΛΛ$ reaction may test dynamical mechanisms invoked to explain the proton spin puzzle revealed by polarized deep--inelastic scattering experiments. In particular, models with {\it negatively} polarized $\bar{s}s$ pairs in the proton wave function predict $D_{nn}<0$, whereas models with {\it positively} polarized gluons would predict $D_{nn}>0$.

hep-ph↗
arXiv1994

Abundant phi-Meson Production in pbar-p Annihilation at Rest and Strangeness in the Nucleon

A large apparent violation of the OZI rule has recently been found in many channels in pbar-p annihilation LEAR. An interpretation of these data in terms of the "shake-out" and "rearrangement" of an intrinsic sbar-s component of the nucleon wave function is proposed. This gives a channel-dependent, non-universal modification of the naive OZI prediction. Within this approach, we interpret the strong excess of $ϕ$ production in S-wave pbar-p annihilations in terms of the polarization of the nucleon's sbar-s component indicated by deep inelastic lepton-nucleon scattering experiments. This interpretation could be tested by measurements of the $f_2'(1525)/f_2(1270)$ production ratio in P-wave annihilations and by experiments with polarized beams and polarized targets. We also propose a test of the intrinsic strangeness hypothesis in $ϕ$ production in high-momentum transfer processes, via a difference in constituent counting rules from gluon-mediated production.

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arXiv1994

A Non-Critical String Approach to Black Holes, Time and Quantum Dynamics

We review our approach to time and quantum dynamics based on non-critical string theory, developing its relationship to previous work on non-equilibrium quantum statistical mechanics and the microscopic arrow of time. We exhibit specific non-factorizing contributions to the ${\nd S}$ matrix associated with topological defects on the world sheet, explaining the rôle that the leakage of ${W_{\infty}}$ charges plays in the loss of quantum coherence. We stress the analogy with the quantum Hall effect, discuss the violation of $CPT$, and also apply our approach to cosmology.

hep-th↗
arXiv1994

Some Physical Aspects of Liouville String Dynamics

We discuss some physical aspects of our Liouville approach to non-critical strings, including the emergence of a microscopic arrow of time, effective field theories as classical ``pointer'' states in theory space, $CPT$ violation and the possible apparent non-conservation of angular momentum. We also review the application of a phenomenological parametrization of this formalism to the neutral kaon system.

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arXiv1993

A Liouville String Approach to Microscopic Time and Cosmology

In the non-critical string framework that we have proposed recently, the time $t$ is identified with a dynamical local renormalization group scale, the Liouville mode, and behaves as a statistical evolution parameter, flowing irreversibly from an infrared fixed point - which we conjecture to be a topological string phase - to an ultraviolet one - which corresponds to a static critical string vacuum. When applied to a toy two-dimensional model of space-time singularities, this formalism yields an apparent renormalization of the velocity of light, and a $t$-dependent form of the uncertainty relation for position and momentum of a test string. We speculate within this framework on a stringy alternative to conventional field-theoretical inflation, and the decay towards zero of the cosmological constant in a maximally-symmetric space.

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arXiv1993

Flipped Angles and Phases: A Systematic Study

We discuss systematically the fermion mass and mixing matrices in a generic \linebreak field-theoretical flipped $SU(5)$ model, with particular applications to neutrino and baryon number-changing physics. We demonstrate that the different quark flavour branching ratios in proton decay are related to the Cabibbo-Kobayashi-Maskawa angles, whereas the lepton flavour branching ratios are undetermined. The light neutrino mixing angles observable via oscillation effects are related to the heavy conjugate (right-handed) neutrino mass matrix, which also plays a key role in cosmological baryogenesis. The ratios of neutrino and charged lepton decay modes in baryon decay may also be related to neutrino oscillation parameters. Plausible Ansätze for the generation structure of coupling matrices motivate additional relations between physical observables, and yield a satisfactory baryon asymmetry.

hep-ph↗
arXiv1993

Perturbative QCD data are consistent with light gluinos

We discuss systematically the consistency of light gluinos with data on perturbative QCD from deep inelastic scattering, quarkonia, jets at LEP, and the total hadronic cross-section in ${e^+ e^-}$ annihilation on the $Z$ peak and elsewhere. We demonstrate that, in addition to the well-known increase in the value of $α_s(m_Z)$ inferred from lower-energy data due to the slower running of $α_s$ in the presence of light gluinos, the value of $α_s(m_Z)$ extracted from the LEP data must also be $increased$, as a result of including the effects of virtual light gluinos. The effect of these increases in other estimates of $α_s(m_Z)$ is to make them more consistent with the value extracted from the total $e^+ e^-$ cross-section, which would otherwise appear distinctly higher. We discuss the possibility of looking for light gluinos in four-jet events at LEP, and their possible implications for scaling violations at HERA.

hep-ph↗
arXiv1993

On the Baryon, Lepton-Flavour and Right-Handed Electron Asymmetries of the Universe

Non-perturbative electroweak effects, in thermal equilibrium in the early universe, have the potential to erase the baryon asymmetry of the universe, unless it is encoded in a B-L asymmetry, or in some "accidentally" conserved quantity. We first consider the possibility that the BAU may be regenerated from lepton flavour asymmetries even when initially $B-L = 0$. We show that provided some, but {\it not} all the lepton flavours are violated by $ΔL{\neq}0$ interactions in equilibrium, the BAU may be regenerated without lepton mass effects. We next examine the possibility of encoding the baryon asymmetry in a primordial asymmetry for the right-handed electron, which due to its weak Yukawa interaction only comes into chemical equilibrium as the sphalerons are falling out of equilibrium. This would also raise the possibility of preserving an initial baryon asymmetry when $B-L = 0$.

hep-ph↗
arXiv1992

CPT Violation in String-Modified Quantum Mechanics and the Neutral Kaon System

We show that $CPT$ is in general violated in a non-quantum-mechanical way in the effective low-energy theory derived from string theory, as a result of apparent world-sheet charge non-conservation induced by stringy monopoles corresponding to target-space black hole configurations. This modification of quantum mechanics does not violate energy conservation. The magnitude of this effective spontaneous violation of $CPT$ may not be be far from the present experimental sensitivity in the neutral kaon system. We demonstrate that our previously proposed stringy modifications to the quantum-mechanical description of the neutral kaon system violate $CPT$, although in a different way from that assumed in phenomenological analyses within conventional quantum mechanics. We constrain the novel $CPT$-violating parameters using available data on $K_L \rightarrow 2π$, $K_S \rightarrow 3π^0$ and semileptonic $K_{L,S}$ decay asymmetries. We demonstrate that these data and an approximate treatment of interference effects in $K \rightarrow 2π$ decays are consistent with a {\it non-vanishing} amount of $CPT$ violation at a level accessible to a new round of experiments, and further data and/or analysis are required to exclude the extreme possibility that they dominate over $CP$ violation. Could non-quantum-field theoretical and non-quantum-mechanical $CPT$ violation usher in the long-awaited era of string phenomenology?}

hep-th↗
arXiv1992

Flipped Heavy Neutrinos from the Solar Neutrino Problem to Baryogenesis

We discuss baryogenesis using the flipped $SU(5)$ model for lepton mass matrices. We show that the generalized see-saw mechanism in this model can not only provide MSW neutrino mixing suitable for solving the solar neutrino problem, and supply a hot dark matter candidate ($ν_τ$) with mass $0(10)eV$ as indicated by recent COBE results, but can also naturally account for the baryon asymmetry of the universe. Heavy singlet neutrino decay generates a net lepton asymmetry which is subsequently reprocessed by nonperturbative electroweak interactions. We evaluate the baryon asymmetry so produced in light of the constraints that the COBE observations put on inflationary cosmologies, finding it comfortably consistent with observation.

hep-ph↗
arXiv1992

The prospects for CHORUS and NOMAD in the light of COBE and GALLEX

The most natural MSW neutrino oscillation interpretation of the GALLEX and other solar neutrino data, which invokes $m_{ν_μ}\sim3\times10^{-3}\eV$, and a general GUT see-saw hierarchy of neutrino masses, $m_{ν_{e,μ,τ}}\sim (m_{u,c,t})^2/M_U$, suggest that $m_{ν_τ}\sim10\eV$ in agreement with the preference of COBE and other data on large-scale structure in the Universe for a hot component in the Dark Matter. The general see-saw model also suggests that neutrino mixing angles are related to quark mixing angles, which is also consistent with the oscillation interpretation of the solar neutrino data, and suggests that the forthcoming CHORUS and NOMAD experiments at CERN have a good chance of observing $ν_μ- ν_τ$ oscillations. We present a minimal realization of the general see-saw hierarchy in the context of flipped $SU(5)$.

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arXiv1991

Quantum Mechanics and Black Holes in Four-Dimensional String Theory

In previous papers we have shown how strings in a two-dimensional target space reconcile quantum mechanics with general relativity, thanks to an infinite set of conserved quantum numbers, ``W-hair'', associated with topological soliton-like states. In this paper we extend these arguments to four dimensions, by considering explicitly the case of string black holes with radial symmetry. The key infinite-dimensional W-symmetry is associated with the $\frac{SU(1,1)}{U(1)}$ coset structure of the dilaton-graviton sector that is a model-independent feature of spherically symmetric four-dimensional strings. Arguments are also given that the enormous number of string {\it discrete (topological)} states account for the maintenance of quantum coherence during the (non-thermal) stringy evaporation process, as well as quenching the large Hawking-Bekenstein entropy associated with the black hole. Defining the latter as the measure of the loss of information for an observer at infinity, who - ignoring the higher string quantum numbers - keeps track only of the classical mass,angular momentum and charge of the black hole, one recovers the familiar a quadratic dependence on the black-hole mass by simple counting arguments on the asymptotic density of string states in a linear-dilaton background.

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