arXiv subjects

C. P. Burgess

Publications and source records attributed to C. P. Burgess.

241 records · Page 14Linked to original sources

arXiv1992

Loops, Cutoffs and Anomalous Gauge Boson Couplings

We discuss several issues regarding analyses which use loop calculations to put constraints on anomalous trilinear gauge boson couplings (TGC's). Many such analyses give far too stringent bounds. This is independent of questions of gauge invariance, contrary to the recent claims of de Rujula et. al., since the lagrangians used in these calculations ARE gauge invariant, but the SU(2)_L X U(1)_Y symmetry is nonlinearly realized. The real source of the problem is the incorrect use of cutoffs -- the cutoff dependence of a loop integral does not necessarily reflect the true dependence on the heavy physics scale M. If done carefully, one finds that the constraints on anomalous TGC's are much weaker. We also compare effective lagrangians in which SU(2)_L X U(1)_Y is realized linearly and nonlinearly, and discuss the role of custodial SU(2) in each formulation.

hep-ph↗

arXiv1992

Loop Calculations with Anomalous Gauge Boson Couplings

Analyses which use loop calculations to put constraints on anomalous trilinear gauge boson couplings (TGC's) often give bounds which are much too stringent. The reason has nothing to do with gauge invariance, in contrast to the recent claims of de Rujula et. al., since the lagrangians used in these calculations ARE gauge invariant, with the SU(2)L X U(1)Y symmetry nonlinearly realized. We trace the true cause of the problem to the improper interpretation of cutoffs in the calculation. The point is that the cutoff dependence of a loop integral does not necessarily reflect the true dependence on the heavy physics scale M. We illustrate that, if done carefully, one finds that the true constraints on anomalous TGC's are much weaker.

hep-ph↗

arXiv1992

New Neutrino Physics Without Fine Tuning

We show how a 17 keV neutrino, the solar neutrino problem, and the atmospheric muon-neutrino deficit could all be the low-energy residues of the same pattern of lepton-number breaking at and above the weak scale, with no requirement for fine-tuning a symmetry-breaking scale at lower energies. Talk given at ``Beyond the Standard Model III'', Carleton University, June 1992.

hep-ph↗

arXiv1992

A General Lower Bound for Radiative B Decay

In a wide class of models -- including the standard model -- flavor-changing neutral currents are suppressed by an approximate chiral symmetry of the low-energy lagrangian. This symmetry allows the derivation of general relations among low-energy flavour-changing processes. We derive one such: the relative sizes of the decay rates b --> s gamma, b --> d gamma and s --> d gamma. Together with a unitarity-related lower bound on the rate for the strangeness-changing hyperon decay Omega^- --> Xi^- γwe obtain a reasonably model-independent lower bound for the inclusive b --> s gamma rate.

hep-ph↗

arXiv1992

Light Spin-One Particles Imply Gauge Invariance

Recently, calculations which consider the implications of anomalous trilinear gauge-boson couplings, both at tree-level and in loop-induced processes, have been criticized on the grounds that the lagrangians employed are not \gwk gauge invariant. We prove that, in fact, the general Lorentz-invariant and $U(1)_\em$ invariant but {\it not} $SU_L(2)\times U_Y(1)$ invariant action is equivalent to the general lagrangian in which $SU_L(2)\times U_Y(1)$ appears but is nonlinearly realized. We demonstrate this equivalence in an explicit calculation, and show how it is reconciled with loop calculations in which the different formulations can (superficially) appear to give different answers. In this sense any effective theory containing light spin-one particles is seen to be automatically gauge invariant.

hep-ph↗

arXiv1992

A Natural Framework for Solar and 17 keV Neutrinos

Motivated by recent experimental claims for the existence of a 17 keV neutrino and by the solar neutrino problem, we construct a class of models which contain in their low-energy spectrum a single light sterile neutrino and one or more Nambu-Goldstone bosons. In these models the required pattern of breaking of lepton-number symmetry takes place near the electroweak scale and all mass heirarchies are technically natural. The models are compatible with all cosmological and astrophysical constraints, and can solve the solar neutrino problem via either the MSW effect or vacuum oscillations. The deficit in atmospheric muon neutrinos seen in the Kamiokande and IMB detectors can also be explained in these models.

hep-ph↗

arXiv1991

The Damping of Energetic Gluons and Quarks in High-Temperature QCD

When a gluon or a quark is sent through the hot QCD plasma it can be absorbed into the ambient heat bath and so can acquire an effective lifetime. At high temperatures and for weak couplings the inverse lifetime, or damping rate, for energetic quarks and transverse gluons, (those whose momenta satisfy $|\p| \gg gT$) is given by $γ(\p) = c\; g^2 \log\left({1\over g}\right)\; T + O(g^2T)$. We show that very simple arguments suffice both to fix the numerical coefficient, $c$, in this expression and to show that the $O(g^2T)$ contribution is incalculable in perturbation theory without further assumptions. For QCD with $N_c$ colours we find (expressed in terms of the casimir invariants $C_a=N_c$ and $C_f=(N_c^2-1)/(2N_c)$): $c_g=+{C_a\over 4π}$ for gluons and $c_q=+{C_f\over 4π}$ for quarks. These numbers agree with the more detailed calculations of Pisarski \etal\ but disagree with those of Lebedev and Smilga. The simplicity of the calculation also permits a direct verification of the gauge-invariance and physical sign of the result.

hep-th↗