35,119 research outputs found
Light pseudo-Goldstone bosons without explicit symmetry breaking
A mechanism is discussed to obtain light scalar fields from a spontaneously
broken continuous symmetry without explicitly breaking it. If there is a
continuous manifold of classical vacua in orbit space, its tangent directions
describe classically massless fields that may acquire mass from perturbations
of the potential that do not break the symmetry. We consider the simplest
possible example, involving a scalar field in the adjoint representation of
SU(N). We study the scalar mass spectrum and its RG running at one-loop level
including scalar and pseudoscalar Yukawa couplings to a massive Dirac fermion.Comment: minor typographical changes, 12 pages, 4 figure
Instantons and the singlet-coupling in the chiral quark model
Chiral quark model with a broken-U(3) flavor symmetry can be interpreted as
the effective theory of the instanton-dominated non-perturbative QCD. This
naturally suggests the possibility of a negative singlet/octet coupling ratio,
which has been found, in a previous publication, to be compatible with the
phenomenological description of the nucleon spin-flavor structure.Comment: 9 page
The Casimir effect for parallel plates at finite temperature in the presence of one fractal extra compactified dimension
We discuss the Casimir effect for massless scalar fields subject to the
Dirichlet boundary conditions on the parallel plates at finite temperature in
the presence of one fractal extra compactified dimension. We obtain the Casimir
energy density with the help of the regularization of multiple zeta function
with one arbitrary exponent and further the renormalized Casimir energy density
involving the thermal corrections. It is found that when the temperature is
sufficiently high, the sign of the Casimir energy remains negative no matter
how great the scale dimension is within its allowed region. We derive
and calculate the Casimir force between the parallel plates affected by the
fractal additional compactified dimension and surrounding temperature. The
stronger thermal influence leads the force to be stronger. The nature of the
Casimir force keeps attractive.Comment: 14 pages, 2 figure
Radiative lepton flavor violating decays in the Randall Sundrum background with localized leptons
We study the radiative lepton flavor violating l_i -> l_j\gamma decays in the
two Higgs doublet model, respecting the Randall Sundrum scenario and estimate
the contributions of the KK modes of left (right) handed charged lepton
doublets (singlets) on the branching ratios. We observe that the branching
ratios are sensitive to the contributions of the charged lepton KK modes.Comment: 23 pages, 10 figures, 2 table
Kaluza-Klein Dark Matter
We propose that cold dark matter is made of Kaluza-Klein particles and
explore avenues for its detection. The lightest Kaluza-Klein state is an
excellent dark matter candidate if standard model particles propagate in extra
dimensions and Kaluza-Klein parity is conserved. We consider Kaluza-Klein gauge
bosons. In sharp contrast to the case of supersymmetric dark matter, these
annihilate to hard positrons, neutrinos and photons with unsuppressed rates.
Direct detection signals are also promising. These conclusions are generic to
bosonic dark matter candidates.Comment: 4 pages, 3 figures, discussion of spin-independent cross section
clarified, references added, published versio
The radiative lepton flavor violating decays in the split fermion scenario in the two Higgs doublet model
We study the branching ratios of the lepton flavor violating processes \mu ->
e \gamma, \tau -> e \gamma and \tau -> \mu\gamma in the split fermion scenario,
in the framework of the two Higgs doublet model. We observe that the branching
ratios are relatively more sensitive to the compactification scale and the
Gaussian widths of the leptons in the extra dimensions, for two extra
dimensions and especially for the \tau -> \mu \gamma decay.Comment: 19 pages, 7 Figure
The Fundamental Plane of Gamma-ray Globular Clusters
We have investigated the properties of a group of -ray emitting
globular clusters (GCs) which have recently been uncovered in our Galaxy. By
correlating the observed -ray luminosities with various
cluster properties, we probe the origin of the high energy photons from these
GCs. We report is positively correlated with the encounter rate
and the metalicity which place an
intimate link between the gamma-ray emission and the millisecond pulsar
population. We also find a tendency that increase with the energy
densities of the soft photon at the cluster location. Furthermore, the
two-dimensional regression analysis suggests that , soft photon
densities, and / possibly span fundamental
planes which potentially provide better predictions for the -ray
properties of GCs.Comment: 17 pages, 4 figures, 3 tables, published in Ap
Magnon Dispersion and Anisotropies in SrCu(BO)
We study the dispersion of the magnons (triplet states) in
SrCu(BO) including all symmetry-allowed Dzyaloshinskii-Moriya
interactions. We can reduce the complexity of the general Hamiltonian to a new
simpler form by appropriate rotations of the spin operators. The resulting
Hamiltonian is studied by both perturbation theory and exact numerical
diagonalization on a 32-site cluster. We argue that the dispersion is dominated
by Dzyaloshinskii-Moriya interactions. We point out which combinations of these
anisotropies affect the dispersion to linear-order, and extract their
magnitudes.Comment: 11 pages, 7 figures, 1 table, v2 conclusion shortened, figs clarifie
Internal Anisotropy of Collision Cascades
We investigate the internal anisotropy of collision cascades arising from the
branching structure. We show that the global fractal dimension cannot give an
adequate description of the geometrical structure of cascades because it is
insensitive to the internal anisotropy. In order to give a more elaborate
description we introduce an angular correlation function, which takes into
account the direction of the local growth of the branches of the cascades. It
is demonstrated that the angular correlation function gives a quantitative
description of the directionality and the interrelation of branches. The power
law decay of the angular correlation is evidenced and characterized by an
exponent and an angular correlation length different from the radius of
gyration. It is demonstrated that the overlapping of subcascades has a strong
effect on the angular correlation.Comment: RevteX, 8 pages, 6 .eps figures include
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