138 research outputs found
Turbulence, Complexity, and Solar Flares
The issue of predicting solar flares is one of the most fundamental in
physics, addressing issues of plasma physics, high-energy physics, and
modelling of complex systems. It also poses societal consequences, with our
ever-increasing need for accurate space weather forecasts. Solar flares arise
naturally as a competition between an input (flux emergence and rearrangement)
in the photosphere and an output (electrical current build up and resistive
dissipation) in the corona. Although initially localised, this redistribution
affects neighbouring regions and an avalanche occurs resulting in large scale
eruptions of plasma, particles, and magnetic field. As flares are powered from
the stressed field rooted in the photosphere, a study of the photospheric
magnetic complexity can be used to both predict activity and understand the
physics of the magnetic field. The magnetic energy spectrum and multifractal
spectrum are highlighted as two possible approaches to this.Comment: 2 figure
Strong interactions in air showers
We study the role new gauge interactions in extensions of the standard model
play in air showers initiated by ultrahigh-energy cosmic rays. Hadron-hadron
events remain dominated by quantum chromodynamics, while projectiles and/or
targets from beyond the standard model permit us to see qualitative differences
arising due to the new interactions.Comment: 35 pages, 12 figures. Accepted for publication in JCA
Pseudo Goldstone Bosons Phenomenology in Minimal Walking Technicolor
We construct the non-linear realized Lagrangian for the Goldstone Bosons
associated to the breaking pattern of SU(4) to SO(4). This pattern is expected
to occur in any Technicolor extension of the standard model featuring two Dirac
fermions transforming according to real representations of the underlying gauge
group. We concentrate on the Minimal Walking Technicolor quantum number
assignments with respect to the standard model symmetries. We demonstrate that
for, any choice of the quantum numbers, consistent with gauge and Witten
anomalies the spectrum of the pseudo Goldstone Bosons contains electrically
doubly charged states which can be discovered at the Large Hadron Collider.Comment: 25 pages, 5 figure
Walking Behavior in Technicolored GUTs
There exist two ways to obtain walk behavior: assuming a large number of
technifermions in the fundamental representation of the technicolor (TC) gauge
group, or a small number of technifermions, assuming that these fermions are in
higher-dimensional representations of the TC group. We propose a scheme to
obtain the walking behavior based on technicolored GUTs (TGUTs), where
elementary scalars with the TC degree of freedom may remain in the theory after
the GUT symmetry breaking.Comment: 11 pages, 1 figur
Study of an Alternate Mechanism for the Origin of Fermion Generations
In usual extended technicolor (ETC) theories based on the group
, the quarks of charge 2/3 and -1/3 and the charged
leptons of all generations arise from ETC fermion multiplets transforming
according to the fundamental representation. Here we investigate a different
idea for the origin of SM fermion generations, in which quarks and charged
leptons of different generations arise from ETC fermions transforming according
to different representations of . Although this
mechanism would have the potential, {\it a priori}, to allow a reduction in the
value of relative to conventional ETC models, we show that, at least
in simple models, it is excluded by the fact that the technicolor sector is not
asymptotically free or by the appearance of fermions with exotic quantum
numbers which are not observed.Comment: 6 pages, late
Response, relaxation and transport in unconventional superconductors
We investigate the collision-limited electronic Raman response and the
attenuation of ultrasound in spin-singlet d-wave superconductors at low
temperatures. The dominating elastic collisions are treated within a t-matrix
approximation, which combines the description of weak (Born) and strong
(unitary) impurity scattering. In the long wavelength limit a two-fluid
description of both response and transport emerges. Collisions are here seen to
exclusively dominate the relaxational dynamics of the (Bogoliubov)
quasiparticle system and the analysis allows for a clear connection of response
and transport phenomena. When applied to quasi-2-d superconductors like the
cuprates, it turns out that the transport parameter associated with the Raman
scattering intensity for B1g and B2g photon polarization is closely related to
the corresponding components of the shear viscosity tensor, which dominates the
attenuation of ultrasound. At low temperatures we present analytic solutions of
the transport equations, resulting in a non-power-law behavior of the transport
parameters on temperature.Comment: 22 pages, 3 figure
Energy States of Colored Particle in a Chromomagnetic Field
The unitary transformation, which diagonalizes squared Dirac equation in a
constant chromomagnetic field is found. Applying this transformation, we find
the eigenfunctions of diagonalized Hamiltonian, that describe the states with
definite value of energy and call them energy states. It is pointed out that,
the energy states are determined by the color interaction term of the particle
with the background chromofield and this term is responsible for the splitting
of the energy spectrum.
We construct supercharge operators for the diagonal Hamiltonian, that ensure
the superpartner property of the energy states.Comment: 25 pages, some calculation details have been removed, typos correcte
Electroweak symmetry breaking in other terms
We analyse descriptions of electroweak symmetry breaking in terms of
ultralocal antisymmetric tensor fields and gauge-singlet geometric variables,
respectively; in particular, the Weinberg--Salam model and, ultimately,
dynamical electroweak symmetry breaking by technicolour theories with enhanced
symmetry groups. Our motivation is to unveil the manifestly gauge invariant
structure of the different realisations. We find, for example, parallels to
different types of torsion.Comment: 15p
Infrared Behaviour of The Gluon Propagator in Non-Equilibrium Situations
The infrared behaviour of the medium modified gluon propagator in
non-equilibrium situations is studied in the covariant gauge using the
Schwinger-Keldysh closed-time path formalism. It is shown that the magnetic
screening mass is non-zero at the one loop level whenever the initial gluon
distribution function is non isotropic with the assumption that the
distribution function of the gluon is not divergent at zero transverse
momentum. For isotropic gluon distribution functions, such as those describing
local equilibrium, the magnetic mass at one loop level is zero which is
consistent with finite temperature field theory results. Assuming that a
reasonable initial gluon distribution function can be obtained from a
perturbative QCD calculation of minijets, we determine these out of equilibrium
values for the initial magnetic and Debye screening masses at energy densities
appropriate to RHIC and LHC. We also compare the magnetic masses obtained here
with those obtained using finite temperature lattice QCD methods at similar
temperatures at RHIC and LHC.Comment: 21 pages latex, 4 figures, final version to be published in Phys.
Rev.
A minimal quasiparticle approach for the QGP and its large- limits
We propose a quasiparticle approach allowing to compute the equation of state
of a generic gauge theory with gauge group SU() and quarks in an arbitrary
representation. Our formalism relies on the thermal quasiparticle masses
(quarks and gluons) computed from Hard-Thermal-Loop techniques, in which the
standard two-loop running coupling constant is used. Our model is minimal in
the sense that we do not allow any extra ansatz concerning the
temperature-dependence of the running coupling. We first show that it is able
to reproduce the most recent equations of state computed on the lattice for
temperatures higher than 2 . In this range of temperatures, an ideal gas
framework is indeed expected to be relevant. Then we study the accuracy of
various inequivalent large- limits concerning the description of the QCD
results, as well as the equivalence between the QCD limit and the SUSY Yang-Mills theory. Finally, we estimate the dissociation temperature
of the -meson and comment on the estimations' stability regarding the
different considered large- limits.Comment: 19 pages, 6 figure
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