153 research outputs found
Symmetry breaking and restoring under high pressure: the amazing behaviour of the "simple" alkali metals
We argue that an ionic lattice surrounded by a Fermi liquid changes phase
several times under pressure, oscillating between the symmetric phase and a
low-symmetry dimerized structure, as a consequence of Friedel oscillations in
the pair potential. Phase oscillations explain the tendency towards
dimerization which has been recently reported for the light alkali metals under
high pressure. Moreover, a restoring of the symmetric phase is predicted for
such elements at an even higher density.Comment: accepted in Eur. Phys. J.
Self-consistent variational approach to the minimal left-right symmetric model of electroweak interactions
The problem of mass generation is addressed by a Gaussian variational method
for the minimal left-right symmetric model of electroweak interactions. Without
any scalar bidoublet, the Gaussian effective potential is shown to have a
minimum for a broken symmetry vacuum with a finite expectation value for both
the scalar Higgs doublets. The symmetry is broken by the fermionic coupling
that destabilizes the symmetric vacuum, yielding a self consistent fermionic
mass. In this framework a light Higgs is only compatible with the existence of
a new high energy mass scale below 2 TeV.Comment: 5 pages, 3 figures. New comments added and typing errors in eq. 8 and
11 correcte
Light Higgs bosons from a strongly interacting Higgs sector
The mass and the decay width of a Higgs boson in the minimal standard model
are evaluated by a variational method in the limit of strong self-coupling
interaction. The non-perturbative technique provides an interpolation scheme
between strong-coupling regime and weak-coupling limit where the standard
perturbative results are recovered. In the strong-coupling limit the physical
mass and the decay width of the Higgs boson are found to be very small as a
consequence of mass renormalization. Thus it is argued that the eventual
detection of a light Higgs boson would not rule out the existence of a strongly
interacting Higgs sector.Comment: 2 figure
Grand unification in the minimal left-right symmetric extension of the standard model
The simplest minimal left-right symmetric extension of the standard model is
studied in the high energy limit, and some consequences of the grand
unification hypothesis are explored assuming that the parity breaking scale is
the only relevant energy between the electro-weak scale and the unification
point. While the model is shown to be compatible with the observed neutrino
phenomenology, the parity breaking scale and the heavy boson masses are
predicted to be above 10^7 TeV, quite far from the reach of nowadays
experiments. Below that scale only an almost sterile right handed neutrino is
allowed with a mass M \approx 100 TeV
Gaussian Effective Potential and superconductivity
The Gaussian Effective Potential in a fixed transverse unitarity gauge is
studied for the static three-dimensional U(1) scalar electrodynamics
(Ginzburg-Landau phenomenological theory of superconductivity). In the
broken-symmetry phase the mass of the electromagnetic field (inverse
penetration depth) and the mass of the scalar field (inverse correlation
length) are both determined by solution of the coupled variational equations.
At variance with previous calculations, the choice of a fixed unitarity gauge
prevents from the occurrence of any unphysical degree of freedom. The theory
provides a nice interpolation of the experimental data when approaching the
critical region, where the standard mean-field method is doomed to failure
A general interpolation scheme for thermal fluctuations in superconductors
We present a general interpolation theory for the phenomenological effects of
thermal fluctuations in superconductors. Fluctuations are described by a simple
gauge invariant extension of the gaussian effective potential for the
Ginzburg-Landau static model. The approach is shown to be a genuine variational
method, and to be stationary for infinitesimal gauge variations around the
Landau gauge. Correlation and penetration lengths are shown to depart from the
mean field behaviour in a more or less wide range of temperature below the
critical regime, depending on the class of material considered. The method is
quite general and yields a very good interpolation of the experimental data for
very different materials.Comment: some misprints have been corrected in Eq.(15),(19); more references
and comments have been adde
LABOCA observations of nearby, active galaxies
We present large scale 870 micron maps of the nearby starburst galaxies
NGC253, NGC4945 and the nearest giant elliptical radio galaxy Centaurus A (NGC
5128) obtained with the newly commissioned Large Apex Bolometer Camera (LABOCA)
operated at the APEX telescope. Our continuum images reveal for the first time
the distribution of cold dust at a angular resolution of 20" across the entire
optical disks of NGC253 and NGC4945 out to a radial distance of 10' (7.5 kpc).
In NGC5128 our LABOCA image also shows, for the first time at submillimeter
wavelengths, the synchrotron emission associated with the radio jet and the
inner radio lobes. From an analysis of the 870 micron emission in conjunction
with ISO-LWS, IRAS and long wavelengths radio data we find temperatures for the
cold dust in the disks of all three galaxies of 17-20 K, comparable to the dust
temperatures in the disk of the Milky Way. The total gas mass in the three
galaxies is determined to be 2.1, 4.2 and 2.8 x 10^9 solar masses for NGC253,
NGC4945 and NGC5128, respectively. A detailed comparison between the gas masses
derived from the dust continuum and the integrated CO(1-0) intensity in NGC253
suggests that changes of the CO luminosity to molecular mass conversion factor
are mainly driven by a metallicity gradient and only to a lesser degree by
variations of the CO excitation. An analysis of the synchrotron spectrum in the
northern radio lobe of NGC5128 shows that the synchrotron emission from radio
to the ultraviolet wavelengths is well described by a broken power law and that
the break frequency is a function of the distance from the radio core as
expected for aging electrons. We derive an outflow speed of ~0.5c at a distance
of 2.6kpc from the center, consistent with the speed derived in the vicinity of
the nucleus.Comment: 12 pages, 11 figures. Accepted for publication in A&
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