869 research outputs found
Cosmological Perturbations During Radion Stabilization
We consider the evolution of cosmological perturbations during radion
stabilization, which we assume to happen after a period of inflation in the
early universe. Concentrating on the Randall-Sundrum brane world scenario, we
find that if matter is present both on the positive and negative tension
branes, the coupling of the radion to matter fields could have significant
impact on the evolution of the curvature perturbation and on the production of
entropy perturbations. We investigate both the case of a long-lived and
short-lived radion and outline similarities and differences to the curvaton
scenario.Comment: 13 pages, 15 figures, Revte
Effect of nearest neighbor repulsion on the low frequency phase diagram of a quarter-filled Hubbard-Holstein chain
We have studied the influence of nearest-neighbor (NN) repulsion on the low
frequency phase diagram of a quarter-filled Hubbard-Holstein chain. The NN
repulsion term induces the apparition of two new long range ordered phases (one
CDW for positive and one CDW for
negative ) that did not exist in the V=0 phase diagram. These results
are put into perspective with the newly observed charge ordered phases in
organic conductors and an interpretation of their origin in terms of
electron-molecular vibration coupling is suggested.Comment: 10 pages, 10 figure
Non-tachyonic brane inflation
We consider non-tachyonic hybrid inflation in the context of the braneworld
cosmology. When one considers models for brane inflation, hybrid inflation is a
natural consequence of the tachyon condensation if it appears at the end of
inflation. In this case, however, reheating is a difficult problem due to the
peculiar properties of the tachyon. In this paper we show some models for brane
inflation where a new type of hybrid inflation is realized due to the localized
matter fields. The obvious advantage of our scenario is successful reheating,
which is due to the potential that is localized on the brane. The serious
problem of the loop correction is also avoided.Comment: 14pages, latex2e, references added, final version to appear in PR
F-term, D-term and hybrid brane inflation
We study inflation and reheating in models for the brane universe,
considering hybrid brane inflation without tachyon condensation. We expect that
some fields that are localized on different branes interact with O(1) coupling
when branes are on top of each other, while the interaction vanishes when
branes are separated at a distance. If the interaction is needed to avoid
spontaneous breaking of supersymmetry on the brane, our idea for hybrid brane
inflation works. In our model, when branes are far apart, supersymmetry is
spontaneously broken by the fields on a brane, which induces inflation. The
inflaton field is the moduli for the brane distance. At the end of inflation,
when branes come close, supersymmetry is restored by the interaction between
fields on the branes, then the oscillation starts to reheat the Universe. In
this paper we construct explicit models for F-term and D-term inflation. There
are at least two major advantages. The most attractive point is that reheating
is natural in our model, because the trigger field is not the tachyon but a
conventional field on the brane. The serious constraint from the loop
correction, which always appears in conventional models for hybrid inflation,
is avoided.Comment: 13pages, latex2e, final version, to appear in JCA
The SM and NLO multileg working group: Summary report
This report summarizes the activities of the SM and NLO Multileg Working
Group of the Workshop "Physics at TeV Colliders", Les Houches, France 8-26
June, 2009.Comment: 169 pages, Report of the SM and NLO Multileg Working Group for the
Workshop "Physics at TeV Colliders", Les Houches, France 8-26 June, 200
Asteroseismology and Interferometry
Asteroseismology provides us with a unique opportunity to improve our
understanding of stellar structure and evolution. Recent developments,
including the first systematic studies of solar-like pulsators, have boosted
the impact of this field of research within Astrophysics and have led to a
significant increase in the size of the research community. In the present
paper we start by reviewing the basic observational and theoretical properties
of classical and solar-like pulsators and present results from some of the most
recent and outstanding studies of these stars. We centre our review on those
classes of pulsators for which interferometric studies are expected to provide
a significant input. We discuss current limitations to asteroseismic studies,
including difficulties in mode identification and in the accurate determination
of global parameters of pulsating stars, and, after a brief review of those
aspects of interferometry that are most relevant in this context, anticipate
how interferometric observations may contribute to overcome these limitations.
Moreover, we present results of recent pilot studies of pulsating stars
involving both asteroseismic and interferometric constraints and look into the
future, summarizing ongoing efforts concerning the development of future
instruments and satellite missions which are expected to have an impact in this
field of research.Comment: Version as published in The Astronomy and Astrophysics Review, Volume
14, Issue 3-4, pp. 217-36
Measurement of the Spectroscopy of Orbitally Excited B Mesons at LEP
We measure the masses, decay widths and relative production rate of orbitally
excited B mesons using 1.25 million hadronic Z decays recorded by the L3
detector. B-meson candidates are inclusively reconstructed and combined with
charged pions produced at the primary event vertex. An excess of events above
the expected background in the B\pi mass spectrum in the region 5.6-5.8 GeV is
interpreted as resulting from the decay B_u,d^** -> B^(*)\pi, where B_u,d^**
denotes a mixture of l=1 B-meson states containing a u or a d quark. A fit to
the mass spectrum yields the masses and decay widths of the B_1^* and B_2^*
spin states, as well as the branching fraction for the combination of l=1
states. In addition, evidence is presented for the existence of an excited
B-meson state or mixture of states in the region 5.9-6.0 GeV
Search for Charged Higgs Bosons in e+e- Collisions at \sqrt{s} = 189 GeV
A search for pair-produced charged Higgs bosons is performed with the L3
detector at LEP using data collected at a centre-of-mass energy of 188.6 GeV,
corresponding to an integrated luminosity of 176.4 pb^-1. Higgs decays into a
charm and a strange quark or into a tau lepton and its associated neutrino are
considered. The observed events are consistent with the expectations from
Standard Model background processes. A lower limit of 65.5 GeV on the charged
Higgs mass is derived at 95 % confidence level, independent of the decay
branching ratio Br(H^{+/-} -> tau nu)
The diameter of the CoRoT target HD 49933. Combining the 3D limb darkening, asteroseismology, and interferometry
Context. The interpretation of stellar pulsations in terms of internal
structure depends on the knowledge of the fundamental stellar parameters.
Long-base interferometers permit us to determine very accurate stellar radii,
which are independent constraints for stellar models that help us to locate the
star in the HR diagram. Aims: Using a direct interferometric determination of
the angular diameter and advanced three-dimensional (3D) modeling, we derive
the radius of the CoRoT target HD 49933 and reduce the global stellar parameter
space compatible with seismic data. Methods: The VEGA/CHARA
spectro-interferometer is used to measure the angular diameter of the star. A
3D radiative hydrodynamical simulation of the surface is performed to compute
the limb darkening and derive a reliable diameter from visibility curves. The
other fundamental stellar parameters (mass, age, and Teff) are found by fitting
the large and small p-mode frequency separations using a stellar evolution
model that includes microscopic diffusion. Results: We obtain a limb-darkened
angular diameter of {\theta}LD = 0.445 \pm 0.012 mas. With the Hipparcos
parallax, we obtain a radius of R = 1.42 \pm 0.04 Rsun. The corresponding
stellar evolution model that fits both large and small frequency separations
has a mass of 1.20 \pm 0.08 Msun and an age of 2.7 Gy. The atmospheric
parameters are Teff = 6640 \pm 100 K, log g = 4.21 \pm 0.14, and [Fe/H] =
-0.38.Comment: 4 pages, 4 figure
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