5,451 research outputs found
Gravitational Waves from Abelian Gauge Fields and Cosmic Strings at Preheating
Primordial gravitational waves provide a very important stochastic background
that could be detected soon with interferometric gravitational wave antennas or
indirectly via the induced patterns in the polarization anisotropies of the
cosmic microwave background. The detection of these waves will open a new
window into the early Universe, and therefore it is important to characterize
in detail all possible sources of primordial gravitational waves. In this paper
we develop theoretical and numerical methods to study the production of
gravitational waves from out-of-equilibrium gauge fields at preheating. We then
consider models of preheating after hybrid inflation, where the symmetry
breaking field is charged under a local U(1) symmetry. We analyze in detail the
dynamics of the system in both momentum and configuration space, and show that
gauge fields leave specific imprints in the resulting gravitational wave
spectra, mainly through the appearence of new peaks at characteristic
frequencies that are related to the mass scales in the problem. We also show
how these new features in the spectra correlate with string-like spatial
configurations in both the Higgs and gauge fields that arise due to the
appearance of topological winding numbers of the Higgs around Nielsen-Olesen
strings. We study in detail the time evolution of the spectrum of gauge fields
and gravitational waves as these strings evolve and decay before entering a
turbulent regime where the gravitational wave energy density saturates.Comment: This paper is dedicated to the memory of Lev Kofman. Added references
and comments in Sec. III.B. Version accepted in PR
Antifungal effect and reduction of Ulmus minor symptoms to Ophiostoma novo-ulmi by carvacrol and salicylic acid
There are still no effective means to control Dutch elm disease (DED), caused by the vascular fungi Ophiostoma ulmi and O. novo-ulmi. Plant phenolics may provide a new strategy for DED control, given their known antifungal activity against pathogens and their involvement in plant defence mechanisms. The in vitro antifungal activity of salicylic acid, carvacrol, thymol, phenol, o-cresol, m-cresol, p-cresol, and 2,5-xylenol against the DED pathogens was tested. Also, the protective effect of watering Ulmus minor seedlings with these compounds was tested against O. novo-ulmi. Salicylic acid, carvacrol, and thymol showed the strongest antifungal in vitro activity, while carvacrol and salicylic acid provided the strongest in vivo protection against O. novo-ulmi (63 and 46% reduction of leaf wilting symptoms with respect to controls, respectively). The effect of the treatments on tree phenology was low, and a significant negative relation was observed between the number of days to bud burst and the leaf wilting symptoms after inoculation, probably determined by genetic differences among the elm tree progenies used. The treatments with salicylic acid, carvacrol and thymol induced the highest shift in phenolic metabolite profile with respect to control trees. The protective effect of carvacrol and salicylic acid is discussed in terms of their combined activity as antifungal compounds and as inductors of tree defence responses
A Gravitational Wave Background from Reheating after Hybrid Inflation
The reheating of the universe after hybrid inflation proceeds through the
nucleation and subsequent collision of large concentrations of energy density
in the form of bubble-like structures moving at relativistic speeds. This
generates a significant fraction of energy in the form of a stochastic
background of gravitational waves, whose time evolution is determined by the
successive stages of reheating: First, tachyonic preheating makes the amplitude
of gravity waves grow exponentially fast. Second, bubble collisions add a new
burst of gravitational radiation. Third, turbulent motions finally sets the end
of gravitational waves production. From then on, these waves propagate
unimpeded to us. We find that the fraction of energy density today in these
primordial gravitational waves could be significant for GUT-scale models of
inflation, although well beyond the frequency range sensitivity of
gravitational wave observatories like LIGO, LISA or BBO. However, low-scale
models could still produce a detectable signal at frequencies accessible to BBO
or DECIGO. For comparison, we have also computed the analogous gravitational
wave background from some chaotic inflation models and obtained results similar
to those found by other groups. The discovery of such a background would open a
new observational window into the very early universe, where the details of the
process of reheating, i.e. the Big Bang, could be explored. Moreover, it could
also serve in the future as a new experimental tool for testing the
Inflationary Paradigm.Comment: 22 pages, 18 figures, uses revtex
Local and average fields inside surface-disordered waveguides: Resonances in the one-dimensional Anderson localization regime
We investigate the one-dimensional propagation of waves in the Anderson
localization regime, for a single-mode, surface disordered waveguide. We make
use of both an analytical formulation and rigorous numerical simulation
calculations. The occurrence of anomalously large transmission coefficients for
given realizations and/or frequencies is studied, revealing huge field
intensity concentration inside the disordered waveguide. The analytically
predicted s-like dependence of the average intensity, being in good agreement
with the numerical results for moderately long systems, fails to explain the
intensity distribution observed deep in the localized regime. The average
contribution to the field intensity from the resonances that are above a
threshold transmission coefficient is a broad distribution with a large
maximum at/near mid-waveguide, depending universally (for given ) on the
ratio of the length of the disorder segment to the localization length,
. The same universality is observed in the spatial distribution of the
intensity inside typical (non-resonant with respect to the transmission
coefficient) realizations, presenting a s-like shape similar to that of the
total average intensity for close to 1, which decays faster the lower
is . Evidence is given of the self-averaging nature of the random
quantity . Higher-order moments of the intensity are
also shown.Comment: 9 pages, 9 figure
Magnetic Field Effects on the Transport Properties of One-sided Rough Wires
We present a detailed numerical analysis of the effect of a magnetic field on
the transport properties of a `small-' one-sided surface disordered wire.
When time reversal symmetry is broken due to a magnetic field , we find a
strong increase with not only of the localization length but also of
the mean free path caused by boundary states. Despite this, the
universal relationship between and does hold. We also analyze the
conductance distribution at the metal-insulator crossover, finding a very good
agreement with Random Matrix Theory with two fluctuating channels within the
Circular Orthogonal(Unitary) Ensemble in absence(presence) of Comment: 5 pages, 4 figures, to appear in Phys. Rev.
Reflection and transmission of waves in surface-disordered waveguides
The reflection and transmission amplitudes of waves in disordered multimode
waveguides are studied by means of numerical simulations based on the invariant
embedding equations. In particular, we analyze the influence of surface-type
disorder on the behavior of the ensemble average and fluctuations of the
reflection and transmission coefficients, reflectance, transmittance, and
conductance. Our results show anomalous effects stemming from the combination
of mode dispersion and rough surface scattering: For a given waveguide length,
the larger the mode transverse momentum is, the more strongly is the mode
scattered. These effects manifest themselves in the mode selectivity of the
transmission coefficients, anomalous backscattering enhancement, and speckle
pattern both in reflection and transmission, reflectance and transmittance, and
also in the conductance and its universal fluctuations. It is shown that, in
contrast to volume impurities, surface scattering in quasi-one-dimensional
structures (waveguides) gives rise to the coexistence of the ballistic,
diffusive, and localized regimes within the same sample.Comment: LaTeX (REVTeX), 12 pages with 14 EPS figures (epsf macro), minor
change
Estratigrafía Sísmica de Alta Resolución en las Rías Baixas: Pontevedra y Vigo (NO España)
El estudio detallado de los perfiles de sísmica reflexión de alta resolución, de las rías de Pontevedra y Vigo ha permitido diferenciar 7 unidades sísmicas. Las unidades sísmicas Bg y Bm se interpretan como correspondientes a rocas del basamento, graníticas y metamórficas respectivamente. Las 5 unidades sísmicas restantes corresponden al relleno sedimentario de las rías. La identificación de los límites de secuencia L2 y L3 permiten reconocer tres secuencias sedimentarias (S1, S2 y S3), de más antigua a más reciente, que van marcando una progresiva ampliación de la zona de sedimentación en las rías. En la secuencia más reciente (S3) destaca la presencia de apantallamientos acústicos y/o formas de escape, interpretadas como debidas a la presencia de gas biogénico en los sedimentos.Detailed study of high-resolution seismic reflection profiles of the Ría de Pontevedra and Vigo (NW Spain) has allowed to distinguish 7 seismic units. Seismic units Bg and Bm are interpreted as granitic and methamorphic basement rocks respectively. The other 5 seismic units correspond to the sedimentary infill of the rías. The identification of the sequences boundaries L2 and L3 allow to recognize three sedimentary sequences (S1, S2 and S3), from oldest to youngest, 217 S. García-Gil et al. Estratigrafía sísmica de alta resolución en las Rías Baixas:... that give a progressive enlargement of the rías sedimentary basin. In the most recent sequence (S3) appear acoustic blanking and/or escape features, interpreted as due to the presence of biogenic gas in the sediments of the rías
On the Transverse-Traceless Projection in Lattice Simulations of Gravitational Wave Production
It has recently been pointed out that the usual procedure employed in order
to obtain the transverse-traceless (TT) part of metric perturbations in lattice
simulations was inconsistent with the fact that those fields live in the
lattice and not in the continuum. It was claimed that this could lead to a
larger amplitude and a wrong shape for the gravitational wave (GW) spectra
obtained in numerical simulations of (p)reheating. In order to address this
issue, we have defined a consistent prescription in the lattice for extracting
the TT part of the metric perturbations. We demonstrate explicitly that the GW
spectra obtained with the old continuum-based TT projection only differ
marginally in amplitude and shape with respect to the new lattice-based ones.
We conclude that one can therefore trust the predictions appearing in the
literature on the spectra of GW produced during (p)reheating and similar
scenarios simulated on a lattice.Comment: 22 pages, 8 figures, Submitted to JCA
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