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.Comment: talk presented at the XXVI International Conference on High Energy Physics, Dallas, USA, August 1992, plain TeX, 12 pages, 3 figures (not included), UdeM-LPN-TH-105, McGill-92/3

Probing New Physics via an Angular Analysis of B --> V1 V2 decays

We show that an angular analysis of B --> V1 V2 decays yields numerous tests for new physics in the decay amplitudes. Unlike direct CP asymmetries, many of these new-physics observables are nonzero even if the strong phase differences vanish. For certain observables, neither time-dependent measurements nor tagging is necessary. Should a signal for new physics be found, one can place a lower limit on the size of the new-physics parameters, as well as on their effect on the measurement of the phase of B0--Bbar0 mixing.Comment: 9 pages, plain latex, no figures. Title modified slightly. Paragraph added about viability of method. Conclusions unchanged. To be published in Europhysics Letter

All-optical reconstruction of atomic ground-state population

The population distribution within the ground-state of an atomic ensemble is of large significance in a variety of quantum optics processes. We present a method to reconstruct the detailed population distribution from a set of absorption measurements with various frequencies and polarizations, by utilizing the differences between the dipole matrix elements of the probed transitions. The technique is experimentally implemented on a thermal rubidium vapor, demonstrating a population-based analysis in two optical pumping examples. The results are used to verify and calibrate an elaborated numerical model, and the limitations of the reconstruction scheme which result from the symmetry properties of the dipole matrix elements are discussed.Comment: 6 pages, 4 figure

Vortex Penetration into a Type II Superconductor due to a Mesoscopic External Current

Applying the London theory we study curved vortices produced by an external current near and parallel to the surface of a type II superconductor. By minimizing the energy functional we find the contour describing the hard core of the flux line, and predict the threshold current for entrance of the first vortex. We assume that the vortex entrance is allowed due to surface defects, despite the Bean-Livingston barrier. Compared to the usual situation with a homogeneous magnetic field, the main effect of the present geometry is that larger magnetic fields can be applied locally before vortices enter the superconducting sample. It is argued that this effect can be further enhanced in anisotropic superconductors.Comment: 9 pages, 14 figure

Can one detect new physics in I=0 and/or I=2 contributions to the decays B --> pi pi?

We study the effects of new-physics contributions to B --> pi pi decays, which can be parametrized as four new complex quantities. A simple analysis is provided by utilizing the reparametrization invariance of the decay amplitudes. We find that six quantities can be reabsorbed into the definitions of Standard Model-like parameters. As a result, the usual isospin analysis provides only two constraints on new physics which are independent of estimates for the Standard Model contributions. In particular, we show that one is not sensitive to new physics affecting the I=0 amplitudes. On the other hand, I=2 new physics can be detected, and its parameters can be measured by using independent determinations of the weak phases. We obtain constraints on these new-physics parameters through a fit to the current experimental data.Comment: 8 pages, RevTe

Effects of disorder on the vortex charge

We study the influence of disorder on the vortex charge, both due to random pinning of the vortices and due to scattering off non-magnetic impurities. In the case when there are no impurities present, but the vortices are randomly distributed, the effect is very small, except when two or more vortices are close by. When impurities are present, they have a noticeable effect on the vortex charge. This, together with the effect of temperature, changes appreciably the vortex charge. In the case of an attractive impurity potential the sign of the charge naturally changes.Comment: 10 pages, 16 figures. Accepted in Phys. Rev.