7,992 research outputs found
Cosmological Constraints on Late-time Entropy Production
We investigate cosmological effects concerning the late-time entropy
production due to the decay of non-relativistic massive particles. The
thermalization process of neutrinos after the entropy production is properly
solved by using the Boltzmann equation. If a large entropy production takes
place at late time t 1 sec, it is found that a large fraction of
neutrinos cannot be thermalized. This fact loosens the tight constraint on the
reheating temperature T_R from the big bang nucleosynthesis and T_R could be as
low as 0.5 MeV. The influence on the large scale structure formation and cosmic
microwave background anisotropies is also discussed.Comment: 4 pages, using RevTeX and five postscript figures, comments added, to
appear in Phys. Rev. Let
Critical behavior of self-assembled rigid rods on triangular and honeycomb lattices
Using Monte Carlo simulations and finite-size scaling analysis, the critical
behavior of self-assembled rigid rods on triangular and honeycomb lattices at
intermediate density has been studied. The system is composed of monomers with
two attractive (sticky) poles that, by decreasing temperature or increasing
density, polymerize reversibly into chains with three allowed directions and,
at the same time, undergo a continuous isotropic-nematic (IN) transition. The
determination of the critical exponents, along with the behavior of Binder
cumulants, indicate that the IN transition belongs to the q=1 Potts
universality class.Comment: 6 pages, 5 figure
A Study of Gaussianity in CMB band maps
The detection of non-Gaussianity in the CMB data would rule out a number of
inflationary models. A null detection of non-Gaussianity, instead, would
exclude alternative models for the early universe. Thus, a detection or
non-detection of primordial non-Gaussianity in the CMB data is crucial to
discriminate among inflationary models, and to test alternative scenarios.
However, there are various non-cosmological sources of non-Gaussianity. This
makes important to employ different indicators in order to detect distinct
forms of non-Gaussianity in CMB data. Recently, we proposed two new indicators
to measure deviation from Gaussianity on large angular scales, and used them to
study the Gaussianity of the raw band WMAP maps with and without the KQ75 mask.
Here we extend this work by using these indicators to perform similar analyses
of deviation from Gaussianity of the foreground-reduced Q, V, and W band maps.
We show that there is a significant deviation from Gaussianity in the
considered full-sky maps, which is reduced to a level consistent with
Gaussianity when the KQ75 mask is employed.Comment: 5 pages, 2 PS figures, uses ws-ijmpd.cls ; to be published in the
International Journal of Modern Physics
Value Encoding in Single Neurons in the Human Amygdala during Decision Making
A growing consensus suggests that the brain makes simple choices by assigning values to the stimuli under consideration and then comparing these values to make a decision. However, the network involved in computing the values has not yet been fully characterized. Here, we investigated whether the human amygdala plays a role in the computation of stimulus values at the time of decision making. We recorded single neuron activity from the amygdala of awake patients while they made simple purchase decisions over food items. We found 16 amygdala neurons, located primarily in the basolateral nucleus that responded linearly to the values assigned to individual items
Spectrum of Background X-rays from Moduli Dark Matter
We examine the -ray spectrum from the decay of the dark-matter moduli with
mass keV, in particular, paying attention to the line
spectrum from the moduli trapped in the halo of our galaxy. It is found that
with the energy resolution of the current experiments (%) the line
intensity is about twice stronger than that of the continuum spectrum from the
moduli that spread in the whole universe. Therefore, in the future experiments
with higher energy resolutions it may be possible to detect such line photons.
We also investigate the -ray spectrum emitted from the decay of the
multi-GeV moduli. It is shown that the emitted photons may form MeV-bump in the
-ray spectrum. We also find that if the modulus mass is of the order of
10 GeV, the emitted photons at the peak of the continuum spectrum loses their
energy by the scattering and the shape of the spectrum is significantly
changed, which makes the constraint weaker than that obtained in the previous
works.Comment: 14 pages (RevTeX file) including four postscript figures, reviced
version to be published in Physical Review
Scaling of the anomalous Hall effect in SrCaRuO
The anomalous Hall effect (AHE) of ferromagnetic thin films of
SrCaRuO (0 0.4) is studied as a function of
and temperature . As increases, both the transition temperature
and the magnetization are reduced and vanish near 0.7. For all
compositions, the transverse resistivity varies non-monotonously
with , and even changes sign, thus violating the conventional expression
( is the magnetic induction, while
and are the ordinary and anomalous Hall coefficients). From the rather
complicated data of , we find a scaling behavior of the transverse
conductivity with , which is well reproduced by the
first-principles band calculation assuming the intrinsic origin of the AHE.Comment: REVTeX 4 style; 5 pages, 3 figures; revised 23/2 and accepted for
publicatio
Chaotic hybrid new inflation in supergravity with a running spectral index
We propose an inflation model in supergravity, in which chaotic and hybrid
inflation occurs successively, followed by new inflation. During hybrid
inflation, adiabatic fluctuations with a running spectral index with \ns >1
on a large scale and \ns <1 on a smaller scale are generated, as favored by
recent results of the first year Wilkinson Microwave Anisotropy Probe. The
initial condition of new inflation is also set dynamically during hybrid
inflation, and its duration and the amplitude of density fluctuations take
appropriate values to help early star formation to realize early reionization.Comment: 15 pages, to appear in Phys. Rev.
Cosmological Constraints on Neutrino Injection
We derive general constraints on the relic abundances of a long-lived
particle which mainly decays into a neutrino (and something else) at
cosmological time scales. Such an exotic particle may show up in various
particle-physics models based on physics beyond the standard model. The
constraints are obtained from big-bang nucleosynthesis, cosmic microwave
background and diffuse neutrino and photon fluxes, depending on the lifetime
and the electromagnetic and hadronic branching ratios.Comment: 33 pages, 23 figure
Evidence for a full energy gap for nickel-pnictide LaNiAsO_{1-x}F_x superconductors by ^{75}As nuclear quadrupole resonance
We report systematic ^{75}As-NQR and ^{139}La-NMR studies on nickel-pnictide
superconductors LaNiAsO_{1-x}F_x (x=0, 0.06, 0.10 and 0.12). The spin lattice
relaxation rate 1/T_1 decreases below T_c with a well-defined coherence peak
and follows an exponential decay at low temperatures. This result indicates
that the superconducting gap is fully opened, and is strikingly different from
that observed in iron-pnictide analogs. In the normal state, 1/T_1T is constant
in the temperature range T_c \sim 4 K < T <10 K for all compounds and up to
T=250 K for x=0 and 0.06, which indicates weak electron correlations and is
also different from the iron analog. We argue that the differences between the
iron and nickel pnictides arise from the different electronic band structure.
Our results highlight the importance of the peculiar Fermi-surface topology in
iron-pnictides.Comment: 4 pages, 5 figure
Antiferromagnetic Spin Fluctuation above the Superconducting Dome and the Full-Gaps Superconducting State in LaFeAsO1-xFx Revealed by 75As-Nuclear Quadrupole Resonance
We report a systematic study by 75As nuclear-quadrupole resonance in
LaFeAsO1-xFx. The antiferromagnetic spin fluctuation (AFSF) found above the
magnetic ordering temperature TN = 58 K for x = 0.03 persists in the regime
0.04 < x < 0.08 where superconductivity sets in. A dome-shaped x-dependence of
the superconducting transition temperature Tc is found, with the highest Tc =
27 K at x = 0.06 which is realized under significant AFSF. With increasing x
further, the AFSF decreases, and so does Tc. These features resemble closely
the cuprates La2-xSrxCuO4. In x = 0.06, the spin-lattice relaxation rate (1/T1)
below Tc decreases exponentially down to 0.13 Tc, which unambiguously indicates
that the energy gaps are fully-opened. The temperature variation of 1/T1 below
Tc is rendered nonexponential for other x by impurity scattering.Comment: 5 pages, 5 figures, more references adde
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