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Bruce H. J. McKellar

Publications and source records attributed to Bruce H. J. McKellar.

At least 19 recordsLinked to original sources
arXiv2009

Non-Boltzmann behaviour in models of interacting neutrinos

We reconsider the question of the relative importance of single particle effects and correlations in the solvable interacting neutrino models introduced by Friedland and Lunardini and by Bell, Rawlinson and Sawyer. We show, by an exact calculation, that the two particle correlations are not "small", and that they dominate the time evolution in these models, in spite of indications to the contrary from the rate of equilibration. This result holds even after the model in generalized from the original 2 flavor case to $N$ flavors. The failure of the Boltzmann single particle approximation in this model is tentatively attributed to the simplicity of the model, in particular to the assumption that all neutrinos in the initial state are in flavor eigenstates.

hep-ph↗
arXiv2008

(De)quantization of black hole charges

We argue that magnetic and electric charges of the Reissner-Nordstrom black hole are quantized in CP conserving theories. Dequantization phenomenon occurs when CP is broken either explicitly or effectively, and, as a result, pure magnetic black holes are not possible. Two examples illustrating this phenomenon are discussed. One is the electric charge induced by the neutral pion field in a magnetically charged black hole, and another is the electric charge induced due to the massive spin-two field emerging from possible higher curvature terms.

hep-th↗
arXiv2007

Particle interference as a test of Lorentz-violating electrodynamics

In Lorentz-violating electrodynamics a steady current (and similarly a static charge) generates both static magnetic and electric fields. These induced fields, acting on interfering particles, change the interference pattern. We find that particle interference experiments are sensitive to small Lorentz violating effects, and thus they can be used to improve current bounds on some Lorentz-violating parameters.

hep-ph↗
arXiv2006

Construction and analysis of a simplified many-body neutrino model

In dense neutrino systems, such as found in the early Universe, or near a supernova core, neutrino flavor evolution is affected by coherent neutrino-neutrino scattering. It has been recently suggested that many-particle quantum entanglement effects may play an essential role in these systems, potentially invalidating the traditional description in terms of a set of single-particle evolution equations. We model the neutrino system by a system of interacting spins, following an earlier work which showed that such a spin system can in some cases be solved exactly. We extend this work by constructing an exact analytical solution to a more general spin system, including initial states with asymmetric spin distribution and, moreover, not necessarily aligned along the same axis. Our solution exhibits a rich set of behaviors, including coherent oscillations and dephasing and a transition from the classical to quantum regimes. We argue that the classical evolution of the spin system captures the entire coherent behavior of the neutrino system, while the quantum effects in the spin system capture some, but not all, of the neutrino incoherent evolution. By comparing the spin and neutrino systems, we find no evidence for the violation of the accepted one-body description, though the argument involves some subtleties not appreciated before. The analysis in this paper may apply to other two-state systems beyond the neutrino field.

hep-ph↗
arXiv2005

Berry Phase in Neutrino Oscillations

We study the Berry phase in neutrino oscillations for both Dirac and Majorana neutrinos. In order to have a Berry phase, the neutrino oscillations must occur in a varying medium, the neutrino-background interactions must depend on at least two independent densities, and also there must be CP violation if the neutrino interactions with matter are mediated only by the standard model W and Z boson exchanges which implies that there must be at least three generations of neutrinos. The CP violating Majorana phases do not play a role in generating a Berry phase. We show that a natural way to satisfy the conditions for the generation of a Berry phase is to have sterile neutrinos with active-sterile neutrino mixing, in which case at least two active and one sterile neutrinos are required. If there are additional new CP violating flavor changing interactions, it is also possible to have a non-zero Berry phase with just two generations.

hep-ph↗
arXiv2003

Neutrino production, oscillation and detection in the presence of general four-fermion interactions

In this note we investigate the impact of new physics in the form of general four-fermion interactions on neutrino oscillation signals. We develop a field theoretic description of the overall oscillation process which includes the non-standard interactions during the neutrino production, propagation and detection stages. Insights gained during the development of this formalism regarding the possibility of new interactions mimicking neutrino mass differences are expounded. The impact of possible new physics is assessed by studying the $ν_μ\toν_τ$ oscillation channel in vacuum and the $ν_e\to ν_μ$ channel in matter. Although it is known that the effects of new interactions can only act as a perturbation to the leading oscillation parameters, we find that great care needs to be taken when drawing conclusions regarding the strength of new couplings from oscillation measurements.

hep-ph↗
arXiv2003

SU(N) Lattice Gauge Theory on a Single Cube

In this paper we study the viability of persuing analytic variational techniques for the calculation of glueball masses in 3+1 dimensional Hamiltonian lattice gauge theory (LGT) in the pure gauge sector. We discuss the major problems presented by a move from 2+1 to 3+1 dimensions and develop analytic techniques to approximate the integrals appearing in 3+1 dimensional variational glueball mass calculations. We calculate $0^{++}$ and $1^{+-}$ glueball masses on a lattice consisting of a single cube. Despite the use of a very simplistic model, promising signs of an approach to asymptotic scaling is displayed by the SU(N) $1^{+-}$ glueball mass as N is increased.

hep-lat↗
arXiv2003

The Large N Glueball Mass Spectrum in 2+1 Dimensions

In this paper we explore the large N limit of the glueball mass spectrum for 2+1 dimensional pure gauge theory. We employ Hamiltonian lattice gauge theory (LGT) and analytic variational techniques to calculate glueball masses for finite values of N < 26. The results are then accurately extrapolated to infinite N. An empirical observation is discussed which links the infinite N glueball spectrum to a simple oscillator model.

hep-lat↗
arXiv2003

SU(N) Glueball Masses in 2+1 Dimensions

We calculate the masses of the lowest lying eigenstates of improved SU(2), SU(3), SU(4) and SU(5) Hamiltonian lattice gauge theory (LGT) in 2+1 dimensions using an analytic variational approach. The ground state is approximated by a one plaquette trial state and mass gaps are calculated in the symmetric and antisymmetric sectors by minimising over a suitable basis of rectangular states. Analytic techniques are developed to handle the group integrals arising in the calculation.

hep-lat↗
arXiv2003

The universal $\ln^{2}s$ increase in total cross sections

While it has long been known that many models of high energy scattering give cross sections which rise as $\ln^{2}s$, the determination of the coefficient of this term is rarely given. We show that in gaussian and exponential eikonal models an exact expression for the cross section can be obtained, which demonstrates the $\ln^{2}s$ asyptoptic behaviour and determines its coefficient. The coefficient is universal, as found empirically, and the value of the constant obtained from the gaussian model is in good agreement with the empirical value.

hep-ph↗
arXiv2001

Constraining R-parity violating couplings from B --> PP decays using QCD improved factorization method

We investigate the role of R-parity violating interaction in the non-leptonic decays of B mesons into two light mesons B --> PP. The decay amplitudes are calculated using the QCD improved factorization method. Using the combined data on B decays from BaBar, Belle and CLEO, we obtain strong constraints on the various products of R-parity violating couplings. Many of these new constraints are stronger than the existing bounds.

hep-ph↗
arXiv2001

Direct Improvement of Hamiltonian Lattice Gauge Theory

We demonstrate that a direct approach to improving Hamiltonian lattice gauge theory is possible. Our approach is to correct errors in the Kogut-Susskind Hamiltonian by incorporating additional gauge invariant terms. The coefficients of these terms are chosen so that the order $a^2$ classical errors vanish. We conclude with a brief discussion of tadpole improvement in Hamiltonian lattice gauge theory.

hep-lat↗
arXiv2001

The Thomas rotation

We review why the Thomas rotation is a crucial facet of special relativity, that is just as fundamental, and just as "unintuitive" and "paradoxical", as such traditional effects as length contraction, time dilation, and the ambiguity of simultaneity. We show how this phenomenon can be quite naturally introduced and investigated in the context of a typical introductory course on special relativity, in a way that is appropriate for, and completely accessible to, undergraduate students. We also demonstrate, in a more advanced section aimed at the graduate student studying the Dirac equation and relativistic quantum field theory, that careful consideration of the Thomas rotation will become vital as modern experiments in particle physics continue to move from unpolarized to polarized cross-sections.

hep-ph↗
arXiv2000

Ruling out the Weinberg Model of Spontaneous CP Violation

There have been many declarations of the death of the Weinberg model of spontaneous CP violation. Previous studies, before the recent measurements of $ε'/ε$, indicated that the model could not accommodate the experimental values on $ε$ in $K^0-\bar K^0$ mixing, the neutron electric dipole moment (EDM), the branching ratio of $b\to s γ$ and the upper limit on $ε'/ε$. We point out that these studies were based on optimistic estimates of the uncertainties in the calculations and that when more realistic estimates of these errors are used the Weinberg model cannot be conclusively ruled out from these considerations alone. Here we use these realistic error estimates to analyze the present situation of the Weinberg model. The latest results from Belle and BaBar on $\sin 2 β$ allow the small values of this parameter which occur naturally in the Weinberg model. However, in this model, the recently measured value of $\Re(ε'/ε) = (1.92\pm 0.25)\times 10^{-3}$ cannot be made compatible with the branching ratio $B(b\to s γ) = (3.15\pm0.54)\times 10^{-4}$. As a result we conclude that the Weinberg model is now confidently and conservatively ruled out.

hep-ph↗
arXiv1999

Gravitational Lensing and Extra Dimensions

We study gravitational lensing and the bending of light in low energy scale (M_S) gravity theories with extra space-time dimensions n. We find that due to the presence of spin-2 Kaluza-Klein states from compactification, a correction to the deflection angle with a strong quadratic dependence on the photon energy is introduced. No deviation from the Einstein General Relativity prediction for the deflection angle for photons grazing the Sun in the visible band with 15% accuracy (90% c.l.) implies that the scale M_S has to be larger than 1.4(2/(n-2))^{1/4} TeV and approximately 4 TeV for n=2. This lower bound is comparable with that from collider physics constraints. Gravitational lensing experiments with higher energy photons can provide stronger constraints.

hep-ph↗
arXiv1997

Classical antiparticles

We review how antiparticles may be introduced in classical relativistic mechanics, and emphasize that many of their paradoxical properties can be more transparently understood in the classical than in the quantum domain.

hep-ph↗
arXiv1995

The Foldy-Wouthuysen transformation

The Foldy-Wouthuysen transformation of the Dirac Hamiltonian is generally taught as simply a mathematical trick that allows one to obtain a two-component theory in the low-energy limit. It is not often emphasized that the transformed representation is the only one in which one can take a meaningful *classical limit*, in terms of particles and antiparticles. We briefly review the history and physics of this transformation.

hep-ph↗