16,410 research outputs found
Testing Models of the Individual and Cosmological Evolutions of Powerful Radio Galaxies
We seek to develop an essentially analytical model for the evolution of
Fanaroff-Riley Class II radio galaxies as they age individually and as their
numbers vary with cosmological epoch. Such modeling is required in order to
probe in more detail the impact of radio galaxies on the growth of structures
in the universe, which appears likely to have been quite significant at z > 1.
In this first paper of a series we compare three rather sophisticated
analytical models for the evolution of linear size and lobe power of FR II
radio galaxies, those of Kaiser, Dennett-Thorpe & Alexander (1997), Blundell,
Rawlings & Willott (1999), and Manolakou & Kirk (2002). We perform
multi-dimensional Monte Carlo simulations in order to compare the predictions
of each model for radio powers, sizes, redshifts and spectral indices with
data. The observational samples used here are the low frequency radio surveys,
3CRR, 6CE and 7CRS, which are flux-limited and complete. We search for and
describe the best parameters for each model, after doing statistical tests on
them. We find that no existing model can give acceptable fits to all the
properties of the surveys considered, although the Kaiser, Dennett-Thorpe &
Alexander (1997) model gives better overall results than do the Manolakou &
Kirk (2002) or Blundell, Rawlings & Willott (1999) models for most of the tests
we performed. We suggest ways in which these models may be improved.Comment: 26 pages, 5 figures; substantially improved version, with additional
statistical tests; to appear in MNRA
Seeing the Invisible Axion in the Sparticle Spectrum
I describe how under favourable circumstances the invisible axion may
manifest its existence at the LHC through the sparticle spectrum; in particular
through a gluino \sim \ln (M_P/m_{3/2}) times heavier than other gauginos.Comment: 4 pages, REVTe
Intrinsic-Density Functionals
The Hohenberg-Kohn theorem and Kohn-Sham procedure are extended to
functionals of the localized intrinsic density of a self-bound system such as a
nucleus. After defining the intrinsic-density functional, we modify the usual
Kohn-Sham procedure slightly to evaluate the mean-field approximation to the
functional, and carefully describe the construction of the leading corrections
for a system of fermions in one dimension with a spin-degeneracy equal to the
number of particles N. Despite the fact that the corrections are complicated
and nonlocal, we are able to construct a local Skyrme-like intrinsic-density
functional that, while different from the exact functional, shares with it a
minimum value equal to the exact ground-state energy at the exact ground-state
intrinsic density, to next-to-leading order in 1/N. We briefly discuss
implications for real Skyrme functionals.Comment: 15 page
Sound Mode Hydrodynamics from Bulk Scalar Fields
We study the hydrodynamic sound mode using gauge/gravity correspondence by
examining a generic black brane background's response to perturbations. We
assume that the background is generated by a single scalar field, and then
generalize to the case of multiple scalar fields. The relevant differential
equations obeyed by the gauge invariant variables are presented in both cases.
Finally, we present an analytical solution to these equations in a special
case; this solution allows us to determine the speed of sound and bulk
viscosity for certain special metrics. These results may be useful in
determining sound mode transport coefficients in phenomenologically motivated
holographic models of strongly coupled systems.Comment: 17 pages. Corrections made to one of the gauge invariant equations
(66). This equation was not used in the other main conclusions of the paper,
so the rest of the results are unchange
Defect behavior, carrier removal and predicted in-space injection annealing of InP solar cells
Defect behavior, observed by deep level transient spectroscopy (DLTS), is used to predict carrier removal and the effects of simultaneous electron irradiation and injection annealing of the performance of InP solar cells. For carrier removal, the number of holes trapped per defect is obtained from measurements of both carrier concentrations and defect concentrations during an isochronal anneal. In addition, from kinetic considerations, the behavior of the dominant defect during injection annealing is used to estimate the degradation expected from exposure to the ambient electron environment in geostationary orbit
Quantum Isometrodynamics
Classical Isometrodynamics is quantized in the Euclidean plus axial gauge.
The quantization is then generalized to a broad class of gauges and the
generating functional for the Green functions of Quantum Isometrodynamics (QID)
is derived. Feynman rules in covariant Euclidean gauges are determined and QID
is shown to be renormalizable by power counting. Asymptotic states are
discussed and new quantum numbers related to the "inner" degrees of freedom
introduced. The one-loop effective action in a Euclidean background gauge is
formally calculated and shown to be finite and gauge-invariant after
renormalization and a consistent definition of the arising "inner" space
momentum integrals. Pure QID is shown to be asymptotically free for all
dimensions of "inner" space whereas QID coupled to the Standard Model
fields is not asymptotically free for D <= 7. Finally nilpotent BRST
transformations for Isometrodynamics are derived along with the BRST symmetry
of the theory and a scetch of the general proof of renormalizability for QID is
given.Comment: 38 page
Physical qubits from charged particles: IR divergences in quantum information
We consider soft photons effects (IR structure of QED) on the construction of
physical qubits. Soft-photons appear when we build charged qubits from the
asymptotic states of QED. This construction is necessary in order to include
the effect of soft photons on entanglement measures. The nonexistence of free
charged particles (due to the long range of QED interactions) lead us to
question the sense of the very concept of free charged qubit. In this letter,
using the "dressing" formalism, we build physical charged qubits from dressed
fields which have the correct asymptotic behavior, are gauge invariant, their
propagators have a particle pole structure and are free from infrared
divergences. Finally, we discuss the impact of the soft corrections on the
entanglement measures.Comment: 4 pages, 2 figures, RevTeX. Version 2: Some references update
Nonrelativistic effective Lagrangians
Chiral perturbation theory is extended to nonrelativistic systems with
spontaneously broken symmetry. In the effective Lagrangian, order parameters
associated with the generators of the group manifest themselves as effective
coupling constants of a topological term, which is gauge invariant only up to a
total derivative. In the case of the ferromagnet, a term connected with the
Brouwer degree dominates the derivative expansion. The general analysis
includes antiferromagnetic magnons and phonons, while the effective field
theory of fluids or gases is beyond the scope of the method.Comment: 30 pages, BUTP-93/2
SU(2) Chiral Sigma Model Study of Phase Transition in Hybrid Stars
We use a modified SU(2) chiral sigma model to study nuclear matter component
and simple bag model for quark matter constituting a neutron star. We also
study the phase transition of nuclear matter to quark matter with the mixed
phase characterized by two conserved charges in the interior of highly dense
neutron stars. Stable solutions of Tolman-Oppenheimer-Volkoff equations
representing hybrid stars are obtained with a maximum mass of 1.67
and radius around 8.9 km.Comment: 14 pages, 5 figure
Effective Field Theory for the Quantum Electrodynamics of a Graphene Wire
We study the low-energy quantum electrodynamics of electrons and holes, in a
thin graphene wire. We develop an effective field theory (EFT) based on an
expansion in p/p_T, where p_T is the typical momentum of electrons and holes in
the transverse direction, while p are the momenta in the longitudinal
direction. We show that, to the lowest-order in (p/p_T), our EFT theory is
formally equivalent to the exactly solvable Schwinger model. By exploiting such
an analogy, we find that the ground state of the quantum wire contains a
condensate of electron-hole pairs. The excitation spectrum is saturated by
electron-hole collective bound-states, and we calculate the dispersion law of
such modes. We also compute the DC conductivity per unit length at zero
chemical potential and find g_s =e^2/h, where g_s=4 is the degeneracy factor.Comment: 7 pages, 2 figures. Definitive version, accepted for publication on
Phys. Rev.
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