5,675 research outputs found
Wave-Packet Revivals for Quantum Systems with Nondegenerate Energies
The revival structure of wave packets is examined for quantum systems having
energies that depend on two nondegenerate quantum numbers. For such systems,
the evolution of the wave packet is controlled by two classical periods and
three revival times. These wave packets exhibit quantum beats in the initial
motion as well as new types of long-term revivals. The issue of whether
fractional revivals can form is addressed. We present an analytical proof
showing that at certain times equal to rational fractions of the revival times
the wave packet can reform as a sum of subsidiary waves and that both
conventional and new types of fractional revivals can occur.Comment: accepted for publication in Physics Letters
Spontaneous Lorentz Violation, Nambu-Goldstone Modes, and Massive Modes
In any theory with spontaneous symmetry breaking, it is important to account
for the massless Nambu-Goldstone and massive Higgs modes. In this short review,
the fate of these modes is examined for the case of a bumblebee model, in which
Lorentz symmetry is spontaneously broken.Comment: 5 pages. Presented at the Fifth Meeting on CPT and Lorentz Symmetry,
Bloomington, Indiana, June 28-July 2, 201
Gravity Theories with Background Fields and Spacetime Symmetry Breaking
An overview is given of effective gravitational field theories with fixed
background fields that break spacetime symmetry. The behavior of the background
fields and the types of excitations that can occur depend on whether the
symmetry breaking is explicit or spontaneous. For example, when the breaking is
spontaneous, the background field is dynamical and massless Nambu--Goldstone
and massive Higgs excitations can appear. However, if the breaking is explicit,
the background is nondynamical, and in this case additional metric or vierbein
excitations occur due to the loss of local symmetry, or these excitations can
be replaced by dynamical scalar fields using a Stuckelberg approach. The
interpretation of Noether identities that must hold in each case differs,
depending on the type of symmetry breaking, and this affects the nature of the
consistency conditions that must hold. The Noether identities also shed light
on why the Stuckelberg approach works, and how it is able to restore the broken
spacetime symmetry in a theory with explicit breaking
Nambu-Goldstone and Massive Modes in Gravitational Theories with Spontaneous Lorentz Breaking
Spontaneous breaking of local Lorentz symmetry is of interest as a possible
mechanism originating from physics at the Planck scale. If such breaking
occurs, however, it raises the questions of what the fate of the
Nambu-Goldstone modes is, whether a Higgs mechanism can occur, and whether
additional massive modes (analogous to the Higgs particle) can appear. A
summary of some recent work looking at these questions is presented here.Comment: Talk presented at the Fourth Meeting on CPT and Lorentz Symmetry,
Bloomington, IN, August, 2007; 7 pages. Typos correcte
QED Tests of Lorentz Symmetry
A status report is given of some recent theoretical and experimental
investigations looking for signals of Lorentz violation in QED. Experiments
with light, charged particles, and atoms have exceptional sensitivity to small
shifts in energy caused by Lorentz violation, including effects that could
originate from new physics at the Planck scale.Comment: Talk presented at the Third Meeting on CPT and Lorentz Symmetry,
Bloomington, IN, August, 2004; 9 page
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