11,553 research outputs found
On the Spectral Analysis of Quantum Electrodynamics with Spatial Cutoffs. I
In this paper, we consider the spectrum of a model in quantum electrodynamics
with a spatial cutoff. It is proven that (1) the Hamiltonian is self-adjoint;
(2) under the infrared regularity condition, the Hamiltonian has a unique
ground state for sufficiently small values of coupling constants. The spectral
scattering theory is studied as well and it is shown that asymptotic fields
exist and the spectral gap is closed
Electronic properties of the novel 4d metallic oxide SrRhO3
The novel 4d perovskite compound SrRhO3 was investigated by isovalent doping
studies. The solubility limits of Ca and Ba onto Sr-site were below 80% and
20%, respectively. Although SrRhO3 was chemically compressed, approximately
5.7% by the Ca doping, no significant influence was observed on the magnetic
and electrical properties.Comment: To be published in a special issue of Physica B (the proceedings of
LT23
Inelastic neutron scattering study on the resonance mode in an optimally doped superconductor LaFeAsOF
An optimally doped iron-based superconductor LaFeAsOF with
K has been studied by inelastic powder neutron scattering. The
magnetic excitation at \AA is enhanced below , leading to
a peak at meV as the resonance mode, in addition to the
formation of a gap at low energy below the crossover energy . The peak energy at \AA corresponds to in
good agreement with the other values of resonance mode observed in the various
iron-based superconductors, even in the high- cuprates. Although the
phonon density of states has a peak at the same energy as the resonance mode in
the present superconductor, the -dependence is consistent with the resonance
being of predominately magnetic origin.Comment: 4 pages, 5 Postscript figure
Occupation probability of harmonic-oscillator quanta for microscopic cluster-model wave functions
We present a new and simple method of calculating the occupation probability
of the number of total harmonic-oscillator quanta for a microscopic
cluster-model wave function. Examples of applications are given to the recent
calculations including -model for He, -model for
Li, and -model for Be as well as the classical
calculations of -model for Li and -model
for C. The analysis is found to be useful for quantifying the amount of
excitations across the major shell as well as the degree of clustering. The
origin of the antistretching effect is discussed.Comment: 9 page
Coherent Cancellation of Photothermal Noise in GaAs/AlGaAs Bragg Mirrors
Thermal noise is a limiting factor in many high-precision optical
experiments. A search is underway for novel optical materials with reduced
thermal noise. One such pair of materials, gallium arsenide and
aluminum-alloyed gallium arsenide (collectively referred to as AlGaAs), shows
promise for its low Brownian noise when compared to conventional materials such
as silica and tantala. However, AlGaAs has the potential to produce a high
level of thermo-optic noise. We have fabricated a set of AlGaAs crystalline
coatings, transferred to fused silica substrates, whose layer structure has
been optimized to reduce thermo-optic noise by inducing coherent cancellation
of the thermoelastic and thermorefractive effects. By measuring the
photothermal transfer function of these mirrors, we find evidence that this
optimization has been successful.Comment: 10 pages, 7 figure
NaV2O4: a Quasi-1D Metallic Antiferromagnet with Half-Metallic Chains
NaV2O4 crystals were grown under high pressure using a NaCl flux, and the
crystals were characterized with X-ray diffraction, electrical resistivity,
heat capacity, and magnetization. The structure of NaV2O4 consists of double
chains of edge-sharing VO6 octahedra. The resistivity is highly anisotropic,
with the resistivity perpendicular to the chains more than 20 times greater
than that parallel to the chains. Magnetically, the intrachain interactions are
ferromagnetic and the interchain interactions are antiferromagnetic; 3D
antiferromagnetic order is established at 140 K. First principles electronic
structure calculations indicate that the chains are half metallic.
Interestingly, the case of NaV2O4 seems to be a quasi-1D analogue of what was
found for half-metallic materials.Comment: 14 pages, including 4 figures and 1 table, accepted for publication
in PR
Non-universal scalar-tensor theories and big bang nucleosynthesis
We investigate the constraints that can be set from big-bang nucleosynthesis
on two classes of models: extended quintessence and scalar-tensor theories of
gravity in which the equivalence principle between standard matter and dark
matter is violated. In the latter case, and for a massless dilaton with
quadratic couplings, the phase space of theories is investigated. We delineate
those theories where attraction toward general relativity occurs. It is shown
that big-bang nucleosynthesis sets more stringent constraints than those
obtained from Solar system tests.Comment: 28 pages, 20 figure
Hyperkahler sigma models on cotangent bundles of Hermitian symmetric spaces using projective superspace
Kahler manifolds have a natural hyperkahler structure associated with (part
of) their cotangent bundles. Using projective superspace, we construct
four-dimensional N = 2 models on the tangent bundles of some classical
Hermitian symmetric spaces (specifically, the four regular series of
irreducible compact symmetric Kahler manifolds, and their non-compact
versions). A further dualization yields the Kahler potential for the
hyperkahler metric on the cotangent bundle.Comment: 47 pages, typos corrected, version accepted by JHE
Probing top charged-Higgs production using top polarization at the Large Hadron Collider
We study single top production in association with a charged Higgs in the
type II two Higgs doublet model at the Large Hadron Collider. The polarization
of the top, reflected in the angular distributions of its decay products, can
be a sensitive probe of new physics in its production. We present theoretically
expected polarizations of the top for top charged-Higgs production, which is
significantly different from that in the closely related process of t-W
production in the Standard Model. We then show that an azimuthal symmetry,
constructed from the decay lepton angular distribution in the laboratory frame,
is a sensitive probe of top polarization and can be used to constrain
parameters involved in top charged-Higgs production.Comment: 22 pages, 18 Figures, Discussions about backgrounds and NLO
corrections added, figures modified, references added, Version published in
JHE
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