5,648 research outputs found
Testing for Features in the Primordial Power Spectrum
Well-known causality arguments show that events occurring during or at the
end of inflation, associated with reheating or preheating, could contribute a
blue component to the spectrum of primordial curvature perturbations, with the
dependence k^3. We explore the possibility that they could be observably large
in CMB, LSS, and Lyman-alpha data. We find that a k^3 component with a cutoff
at some maximum k can modestly improve the fits (Delta chi^2=2.0, 5.4) of the
low multipoles (l ~ 10 - 50) or the second peak (l ~ 540) of the CMB angular
spectrum when the three-year WMAP data are used. Moreover, the results from
WMAP are consistent with the CBI, ACBAR, 2dFGRS, and SDSS data when they are
included in the analysis. Including the SDSS galaxy clustering power spectrum,
we find weak positive evidence for the k^3 component at the level of Delta chi'
= 2.4, with the caveat that the nonlinear evolution of the power spectrum may
not be properly treated in the presence of the k^3 distortion. To investigate
the high-k regime, we use the Lyman-alpha forest data (LUQAS, Croft et al., and
SDSS Lyman-alpha); here we find evidence at the level Delta chi^2' = 3.8.
Considering that there are two additional free parameters in the model, the
above results do not give a strong evidence for features; however, they show
that surprisingly large bumps are not ruled out. We give constraints on the
ratio between the k^3 component and the nearly scale-invariant component, r_3 <
1.5, over the range of wave numbers 0.0023/Mpc < k < 8.2/Mpc. We also discuss
theoretical models which could lead to the k^3 effect, including ordinary
hybrid inflation and double D-term inflation models. We show that the
well-motivated k^3 component is also a good representative of the generic
spikelike feature in the primordial perturbation power spectrum.Comment: 23 pages, 6 figures; added new section on theoretical motivation for
k^3 term, and discussion of double D-term hybrid inflation models; title
changed, added a new section discussing the generic spikelike features,
published in IJMP
Spontaneous Symmetry Breaking in General Relativity. Vector Order Parameter
Gravitational properties of a hedge-hog type topological defect in two extra
dimensions are considered in General Relativity employing a vector as the order
parameter. All previous considerations were done using the order parameter in
the form of a multiplet in a target space of scalar fields. The difference of
these two approaches is analyzed and demonstrated in detail. Regular solutions
of the Einstein equations are studied analytically and numerically. It is shown
that the existence of a negative cosmological constant is sufficient for the
spontaneous symmetry breaking of the initially plain bulk. Regular
configurations have a growing gravitational potential and are able to trap the
matter on the brane. If the energy of spontaneous symmetry breaking is high,
the gravitational potential has several points of minimum. Identical in the
uniform bulk spin-less particles, being trapped within separate minima, acquire
different masses and appear to the observer on brane as different particles
with integer spins.Comment: 23 pages, 6 figure
Narrow-line Laser Cooling by Adiabatic Transfer
We propose and demonstrate a novel laser cooling mechanism applicable to
particles with narrow-linewidth optical transitions. By sweeping the frequency
of counter-propagating laser beams in a sawtooth manner, we cause adiabatic
transfer back and forth between the ground state and a long-lived optically
excited state. The time-ordering of these adiabatic transfers is determined by
Doppler shifts, which ensures that the associated photon recoils are in the
opposite direction to the particle's motion. This ultimately leads to a robust
cooling mechanism capable of exerting large forces via a weak transition and
with reduced reliance on spontaneous emission. We present a simple intuitive
model for the resulting frictional force, and directly demonstrate its efficacy
for increasing the total phase-space density of an atomic ensemble. We rely on
both simulation and experimental studies using the 7.5~kHz linewidth S
to P transition in Sr. The reduced reliance on spontaneous
emission may allow this adiabatic sweep method to be a useful tool for cooling
particles that lack closed cycling transitions, such as molecules.Comment: 5 pages, 4 figure
Mixing-induced CP violating sources for electroweak baryogenesis from a semiclassical approach
The effects of flavor mixing in electroweak baryogenesis is investigated in a
generalized semiclassical WKB approach. Through calculating the nonadiabatic
corrections to the particle currents it is shown that extra CP violation
sources arise from the off-diagonal part of the equation of motion of particles
moving inside the bubble wall. This type of mixing-induced source is of the
first order in derivative expansion of the Higgs condensate, but is oscillation
suppressed. The numerical importance of the mixing-induced source is discussed
in the Minimal Supersymmetric Standard Model and compared with the source term
induced by semiclassical force. It is found that in a large parameter space
where oscillation suppression is not strong enough, the mixing-induced source
can dominate over that from the semiclassical force.Comment: 19 pp, 2 figs, 1 table, some comments added, to appear in
Eur.Phys.J.
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