16,435 research outputs found
Kinematic approach to the mixed state geometric phase in nonunitary evolution
A kinematic approach to the geometric phase for mixed quantal states in
nonunitary evolution is proposed. This phase is manifestly gauge invariant and
can be experimentally tested in interferometry. It leads to well-known results
when the evolution is unitary.Comment: Minor changes; journal reference adde
Magnetic Catalysis in AdS4
We study the formation of fermion condensates in Anti de Sitter space. In
particular, we describe a novel version of magnetic catalysis that arises for
fermions in asymptotically AdS4 geometries which cap off in the infra-red with
a hard wall. We show that the presence of a magnetic field induces a fermion
condensate in the bulk that spontaneously breaks CP symmetry. From the
perspective of the dual boundary theory, this corresponds to a strongly coupled
version of magnetic catalysis in d=2+1.Comment: 22 pages, 4 figures. v2: References added, factors of 2 corrected,
extra comments added in appendix. v3: extra comments about fermion modes in a
hard wall background. v4: A final factor of
A model for luminescence of localized state ensemble
A distribution function for localized carriers,
, is proposed by solving a
rate equation, in which, electrical carriers' generation, thermal escape,
recapture and radiative recombination are taken into account. Based on this
distribution function, a model is developed for luminescence from localized
state ensemble with a Gaussian-type density of states. The model reproduces
quantitatively all the anomalous temperature behaviors of localized state
luminescence. It reduces to the well-known band-tail and luminescence quenching
models under certain approximations.Comment: 14 pages, 4 figure
Neutrino Masses and the LHC: Testing Type II Seesaw
We demonstrate how to systematically test a well-motivated mechanism for
neutrino mass generation (Type-II seesaw) at the LHC, in which a Higgs triplet
is introduced. In the optimistic scenarios with a small Higgs triplet vacuum
expectation value vd < 10^{-4} GeV, one can look for clean signals of lepton
number violation in the decays of doubly charged and singly charged Higgs
bosons to distinguish the Normal Hierarchy (NH), the Inverted Hierarchy (IH)
and the Quasi-Degenerate (QD) spectrum for the light neutrino masses. The
observation of either H+ --> tau+ nubar or H+ --> e+ nubar will be particularly
robust for the spectrum test since they are independent of the unknown Majorana
phases. The H++ decays moderately depend on a Majorana phase Phi2 in the NH,
but sensitively depend on Phi1 in the IH. In a less favorable scenario vd > 2
10^{-4} GeV, when the leptonic channels are suppressed, one needs to observe
the decays H+ --> W+ H_1 and H+ --> t bbar to confirm the triplet-doublet
mixing which in turn implies the existence of the same gauge-invariant
interaction between the lepton doublet and the Higgs triplet responsible for
the neutrino mass generation. In the most optimistic situation, vd approx
10^{-4} GeV, both channels of the lepton pairs and gauge boson pairs may be
available simultaneously. The determination of their relative branching
fractions would give a measurement for the value of vd.Comment: 50 pages, 51 figures, minor corrections, one reference added, to
appear in Physical Review
New Aspects of Geometric Phases in Experiments with polarized Neutrons
Geometric phase phenomena in single neutrons have been observed in
polarimeter and interferometer experiments. Interacting with static and time
dependent magnetic fields, the state vectors acquire a geometric phase tied to
the evolution within spin subspace. In a polarimeter experiment the
non-additivity of quantum phases for mixed spin input states is observed. In a
Si perfect-crystal interferometer experiment appearance of geometric phases,
induced by interaction with an oscillating magnetic field, is verified. The
total system is characterized by an entangled state, consisting of neutron and
radiation fields, governed by a Jaynes-Cummings Hamiltonian. In addition, the
influence of the geometric phase on a Bell measurement, expressed by the
Clauser-Horne-Shimony-Holt (CHSH) inequality, is studied. It is demonstrated
that the effect of geometric phase can be balanced by an appropriate change of
Bell angles.Comment: 17 pages, 9 figure
Gauged vortices in a background
We discuss the statistical mechanics of a gas of gauged vortices in the
canonical formalism. At critical self-coupling, and for low temperatures, it
has been argued that the configuration space for vortex dynamics in each
topological class of the abelian Higgs model approximately truncates to a
finite-dimensional moduli space with a Kaehler structure. For the case where
the vortices live on a 2-sphere, we explain how localisation formulas on the
moduli spaces can be used to compute explicitly the partition function of the
vortex gas interacting with a background potential. The coefficients of this
analytic function provide geometrical data about the Kaehler structures, the
simplest of which being their symplectic volume (computed previously by Manton
using an alternative argument). We use the partition function to deduce simple
results on the thermodynamics of the vortex system; in particular, the average
height on the sphere is computed and provides an interesting effective picture
of the ground state.Comment: Final version: 22 pages, LaTeX, 1 eps figur
Theory of excitons in cubic III-V semiconductor GaAs, InAs and GaN quantum dots: fine structure and spin relaxation
Exciton fine structures in cubic III-V semiconductor GaAs, InAs and GaN
quantum dots are investigated systematically and the exciton spin relaxation in
GaN quantum dots is calculated by first setting up the effective exciton
Hamiltonian. The electron-hole exchange interaction Hamiltonian, which consists
of the long- and short-range parts, is derived within the effective-mass
approximation by taking into account the conduction, heavy- and light-hole
bands, and especially the split-off band. The scheme applied in this work
allows the description of excitons in both the strong and weak confinement
regimes. The importance of treating the direct electron-hole Coulomb
interaction unperturbatively is demonstrated. We show in our calculation that
the light-hole and split-off bands are negligible when considering the exciton
fine structure, even for GaN quantum dots, and the short-range exchange
interaction is irrelevant when considering the optically active doublet
splitting. We point out that the long-range exchange interaction, which is
neglected in many previous works, contributes to the energy splitting between
the bright and dark states, together with the short-range exchange interaction.
Strong dependence of the optically active doublet splitting on the anisotropy
of dot shape is reported. Large doublet splittings up to 600 eV, and even
up to several meV for small dot size with large anisotropy, is shown in GaN
quantum dots. The spin relaxation between the lowest two optically active
exciton states in GaN quantum dots is calculated, showing a strong dependence
on the dot anisotropy. Long exciton spin relaxation time is reported in GaN
quantum dots. These findings are in good agreement with the experimental
results.Comment: 22+ pages, 16 figures, several typos in the published paper are
corrected in re
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