2,340 research outputs found
Inflation: Where Do We Stand?
In this short review, the predictions of inflation are presented and compared
to the most recent measurements of the Cosmic Microwave Background (CMB)
anisotropy. It is argued that inflation is compatible with these observations
but that these ones are not yet accurate enough to probe the details of the
scenario.Comment: 7 pages, no figure, Proceedings of the 8th Workshop on
Non-Perturbative Quantum Chromodynamics, June 7-11, 2004, Pari
On the Reliability of the Langevin Pertubative Solution in Stochastic Inflation
A method to estimate the reliability of a perturbative expansion of the
stochastic inflationary Langevin equation is presented and discussed. The
method is applied to various inflationary scenarios, as large field, small
field and running mass models. It is demonstrated that the perturbative
approach is more reliable than could be naively suspected and, in general, only
breaks down at the very end of inflation.Comment: 7 pages, 3 figure
Interactions and charge fractionalization in an electronic Hong-Ou-Mandel interferometer
We consider an electronic analog of the Hong-Ou-Mandel (HOM) interferometer,
where two single electrons travel along opposite chiral edge states and collide
at a Quantum Point Contact. Studying the current noise, we show that because of
interactions between co-propagating edge states, the degree of
indistinguishability between the two electron wavepackets is dramatically
reduced, leading to reduced contrast for the HOM signal. This decoherence
phenomenon strongly depends on the energy resolution of the packets. Insofar as
interactions cause charge fractionalization, we show that charge and neutral
modes interfere with each other, leading to satellite dips or peaks in the
current noise. Our calculations explain recent experimental results [E.
Bocquillon, et al., Science 339, 1054(2013)] where an electronic HOM signal
with reduced contrast was observed.Comment: 5 pages, 2 figure
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Compressed intramolecular dispersion interactions.
The feasibility of the compression of localized virtual orbitals is explored in the context of intramolecular long-range dispersion interactions. Singular value decomposition (SVD) of coupled cluster doubles amplitudes associated with the dispersion interactions is analyzed for a number of long-chain systems, including saturated and unsaturated hydrocarbons and a silane chain. Further decomposition of the most important amplitudes obtained from these SVDs allows for the analysis of the dispersion-specific virtual orbitals that are naturally localized. Consistent with previous work on intermolecular dispersion interactions in dimers, it is found that three important geminals arise and account for the majority of dispersion interactions at the long range, even in the many body intramolecular case. Furthermore, it is shown that as few as three localized virtual orbitals per occupied orbital can be enough to capture all pairwise long-range dispersion interactions within a molecule
First CMB Constraints on the Inflationary Reheating Temperature
We present the first Bayesian constraints on the single field inflationary
reheating era obtained from Cosmic Microwave Background (CMB) data. After
demonstrating that this epoch can be fully characterized by the so-called
reheating parameter, we show that it is constrained by the seven years
Wilkinson Microwave Anisotropies Probe (WMAP7) data for all large and small
field models. An interesting feature of our approach is that it yields lower
bounds on the reheating temperature which can be combined with the upper bounds
associated with gravitinos production. For large field models, we find the
energy scale of reheating to be higher than those probed at the Large Hadron
Collider, Ereh > 17.3 TeV at 95% of confidence. For small field models, we
obtain the two-sigma lower limits Ereh > 890 TeV for a mean equation of state
during reheating = -0.3 and Ereh > 390 GeV for = -0.2. The
physical origin of these constraints is pedagogically explained by means of the
slow-roll approximation. Finally, when marginalizing over all possible
reheating history, the WMAP7 data push massive inflation under pressure (p <
2.2 at 95% of confidence where p is the power index of the large field
potentials) while they slightly favor super-Planckian field expectation values
in the small field models.Comment: 18 pages, 15 figures, uses RevTeX. References added, matches
published versio
Poissonian tunneling through an extended impurity in the quantum Hall effect
We consider transport in the Poissonian regime between edge states in the
quantum Hall effect. The backscattering potential is assumed to be arbitrary,
as it allows for multiple tunneling paths. We show that the Schottky relation
between the backscattering current and noise can be established in full
generality: the Fano factor corresponds to the electron charge (the
quasiparticle charge) in the integer (fractional) quantum Hall effect, as in
the case of purely local tunneling. We derive an analytical expression for the
backscattering current, which can be written as that of a local tunneling
current, albeit with a renormalized tunneling amplitude which depends on the
voltage bias. We apply our results to a separable tunneling amplitude which can
represent an extended point contact in the integer or in the fractional quantum
Hall effect. We show that the differential conductance of an extended quantum
point contact is suppressed by the interference between tunneling paths, and it
has an anomalous dependence with respect to the bias voltage
The explosion mechanism of core-collapse supernovae: progress in supernova theory and experiments
The explosion of core-collapse supernova depends on a sequence of events
taking place in less than a second in a region of a few hundred kilometers at
the center of a supergiant star, after the stellar core approaches the
Chandrasekhar mass and collapses into a proto-neutron star, and before a shock
wave is launched across the stellar envelope. Theoretical efforts to understand
stellar death focus on the mechanism which transforms the collapse into an
explosion. Progress in understanding this mechanism is reviewed with particular
attention to its asymmetric character. We highlight a series of successful
studies connecting observations of supernova remnants and pulsars properties to
the theory of core-collapse using numerical simulations. The encouraging
results from first principles models in axisymmetric simulations is tempered by
new puzzles in 3D. The diversity of explosion paths and the dependence on the
pre-collapse stellar structure is stressed, as well as the need to gain a
better understanding of hydrodynamical and MHD instabilities such as SASI and
neutrino-driven convection. The shallow water analogy of shock dynamics is
presented as a comparative system where buoyancy effects are absent. This
dynamical system can be studied numerically and also experimentally with a
water fountain. The potential of this complementary research tool for supernova
theory is analyzed. We also review its potential for public outreach in science
museums.Comment: 19 pages, 6 figures, invited review accepted for publication in PAS
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