Bruce A. Campbell

Model independent constraints on leptoquarks from rare processes

We present model independent constraints on the masses and couplings to fermions ofB andL conserving leptoquarks. Such vector or scalar particles could have masses below 100 GeV and be produced at HERA; we list the generation dependent bounds that can be calculated from rare lepton and meson decays, meson-anti-meson mixing and various electroweak tests.

ON THE BARYON, LEPTON-FLAVOUR AND RIGHT-HANDED ELECTRON ASYMMETRIES OF THE UNIVERSE

Abstract 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 not all the lepton flavours are violated by ΔL ≠ 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.

Cosmological baryon asymmetry constraints on extensions of the standard model

Abstract The existence of the baryon asymmetry of the Universe puts strong constraints on extensions of the standard model which violate baryon and/or lepton number. Interactions violating baryon number but conserving lepton number in the early universe could wash away any previously established baryon asymmetry. Interactions which violate lepton number separately (as first discussed by Fukugita and Yanagida), with or without associated violation of baryon number, could combine with non-perturbative baryon and lepton number violating electroweak effects to eradicate the cosmological baryon asymmetry. We derive the constraints on any such interaction of arbitrary dimension arising from the persistence of the cosmological baryon asymmetry. We find, in particular, severe constraints on δB≠0 interactions that could mediate n↔n oscillations or δB≠δL proton decay, and on interactions that could violate R parity in supersymmetric models. These constraints severely limit the potential observability of n- n oscillations and R-parity violation in present laboratory experiments.

Nucleosynthesis and the time dependence of fundamental couplings

Abstract We consider the effects of the time dependence of couplings due to their dependence on a dilaton field, as occurs in superstring theory, as well as in gravity theories of the Jordan-Brans-Dicke type. Because the scale parameters of couplings set by dimensional transmutation depend exponentially on the dilaton vev, we may obtain stringent limits on the shift of the dilaton from the requirement that the induced shift in the couplings not vitiate the successful calculations of element abundances for big-bang nucleosynthesis. These limits can be substantially stronger than those obtained directly from the dilaton-induced change in the gravitational coupling.

Inflation, neutrino baryogenesis, and (s)neutrino-induced baryogenesis

Abstract We evaluate the constraints that the COBE observations put on baryogenesis in inflationary cosmologies. We consider the supersymmetric version of the proposal of Fukugita and Yanagida, that the baryon asymmetry of the universe is created by nonperturbative electroweak reprocessing of a lepton asymmetry generated in the decay of heavy right handed see-saw (s)neutrinos. We review our recent proposal of a mechanism for baryogenesis via sphaleron reprocessing of a lepton asymmetry generated by (s)neutrino mass effects on flat direction scalar condensate oscillations. Finally we analyze in detail the implementation of these mechanisms in the recently proposed ansatze for fermion mass matrices in supersymmetric, unified, theories.

QCD phase transitions in an effective field theory

Abstract We analyze the transitions between hadronic and quark-gluon phases of QCD using an effective low-energy lagrangian for chiral and scale invariance, which embodies quark and gluon condensation. We argue that the quark condensation and deconfinement transitions take place at the same temperature, T q , and that gluon condensation and confinement occur at a common temperature T g . The requirement that scale invariance be spontaneously broken before quarks condense imposes T q ⩽ T q . The gluon transition is in general first order, whereas the quark transition may be second order if T q T g , or first order if T q = T g , which is favoured for large N c . We argue on general grounds and demonstrate with several model calculations that massive hadrons play a key role in driving the gluon transition, and suggest that T g is below the Hagedorn temperature. We also estimate the surface tension for hadronic bubbles forming in a quark-gluon plasma, finding it to be somewhat too small for inhomogeneities to affect the standard calculations of cosmological nucleosynthesis.

Does string theory lead to extended inflation

Abstract We consider the relationship between string theory and currently proposed models of extended inflation. In doing so, we discuss the conformal actions in string theory and in Jordan-Brans-Dicke gravity. We show explicitly the equivalence of pictures in which either gauge or gravitational couplings are changing with time. We demonstrate that the existence of the dilation in string theory does not naturally lead to extended inflation as currently discussed. We also discuss the resolution of the graceful exit problem of old inflation in Einstein gravity using either power-law inflation, or exponential inflation with a changing bubble formation rate.

Search for gluinos

Abstract Simply supersymmetric gauge theories predict the existence of gluinos, massive and long-lived colour octet spin 1/2 partners of the vector gluons. We discuss their phenomenology in e + e − annihilation - focusing on quarkonium decays as well as continuum production - and in deep inelastic scattering experiments - focusing on the energy-momentum sum rule and bremsstrahlung production at high Q 2 . The best lower limit on the gluino mass comes from quarkonium decays and is about 3 GeV.

Reheating and supersymmetric flat-direction baryogenesis

Abstract We re-examine Affleck–Dine baryo/leptogenesis from the oscillation of condensates along flat directions of the supersymmetric standard model, which attained large vevs at the end of the inflationary epoch. The key observation is that superpotential interactions couple the flat directions to other fields, which acquire masses induced by the flat-direction vev that may be sufficiently small for them to be kinematically accessible to inflaton decay. The resulting plasma of inflaton decay products then may act on the flat directions via these superpotential Yukawa couplings, inducing thermal masses and supersymmetry-breaking A terms. In such cases the flat directions start their oscillations at an earlier time than usually estimated. The oscillations are also terminated earlier, due to evaporation of the flat direction condensate produced by its interaction with the plasma of inflaton decay products. In these cases we find that estimates for the resulting baryon/lepton asymmetry of the universe are substantially altered. We identify scenarios for the Yukawa couplings to the flat directions, and the order and mass scale of higher-dimensional superpotential interactions that set the initial flat direction vev, that might lead to acceptable baryo/leptogenesis.

Effective Lagrangian approach to QCD phase transitions

Abstract We use an effective low-energy lagrangian for broken chiral and scale invariance to discuss the condensation and confinement of quarks and of gluons in QCD. The Skyrme model convinces us that quark condensation and confinement are identical, and we argue that well-defined glueball states exist only when gluons condense. Previous calculations with chiral lagrangians have indicated that the quark transition at the finite temperature T q is second order if gluonic degrees of freedom can be neglected, and we argue that the gluonic transition at the finite temperature T g is generically first order. The scaling properties of the effective lagrangian tell us that T q ⩽ T g . We argue that T q can be below T g in SU (2) gauge theory, whereas T q = T g and both quark and gluon transitions are simultaneous and first order in QCD with its SU(3) gauge group. These results agree qualitatively with lattice results. We speculate that the divergent Hagedorn spectrum may drive the joint quark/gluon transition at some temperature below the Hagedorn temperature.