11,297 research outputs found
Sharp ellipticity conditions for ballistic behavior of random walks in random environment
We sharpen ellipticity criteria for random walks in i.i.d. random
environments introduced by Campos and Ram\'{\i}rez which ensure ballistic
behavior. Furthermore, we construct new examples of random environments for
which the walk satisfies the polynomial ballisticity criteria of Berger,
Drewitz and Ram\'{\i}rez. As a corollary, we can exhibit a new range of values
for the parameters of Dirichlet random environments in dimension under
which the corresponding random walk is ballistic.Comment: Published at http://dx.doi.org/10.3150/14-BEJ683 in the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
On uniform closeness of local times of Markov chains and i.i.d. sequences
In this paper we consider the field of local times of a discrete-time Markov
chain on a general state space, and obtain uniform (in time) upper bounds on
the total variation distance between this field and the one of a sequence of
i.i.d. random variables with law given by the invariant measure of that
Markov chain. The proof of this result uses a refinement of the soft local time
method of [11].Comment: 42 pages, 2 figures, coupling construction of Section 4 corrected,
results unchange
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
Trinification, the Hierarchy Problem and Inverse Seesaw Neutrino Masses
In minimal trinification models light neutrino masses can be generated via a
radiative see-saw mechanism, where the masses of the right-handed neutrinos
originate from loops involving Higgs and fermion fields at the unification
scale. This mechanism is absent in models aiming at solving or ameliorating the
hierarchy problem, such as low-energy supersymmetry, since the large
seesaw-scale disappears. In this case, neutrino masses need to be generated via
a TeV-scale mechanism. In this paper, we investigate an inverse seesaw
mechanism and discuss some phenomenological consequences.Comment: 10 pages, 11 figure
Identification of a strong contamination source for graphene in vacuum systems
To minimize parasitic doping effects caused by uncontrolled material
adsorption, graphene is often investigated under vacuum. Here we report an
entirely unexpected phenomenon occurring in vacuum systems, namely strong
n-doping of graphene due to chemical species generated by common ion
high-vacuum gauges. The effect --reversible upon exposing graphene to air-- is
significant, as doping rates can largely exceed 10^{12} cm^{-2}/hour, depending
on pressure and the relative position of the gauge and the graphene device. It
is important to be aware of the phenomenon, as its basic manifestation can be
mistakenly interpreted as vacuum-induced desorption of p-dopants.Comment: 10 pages, 4 figure
Photon Antibunching in the Photoluminescence Spectra of a Single Carbon Nanotube
We report the first observation of photon antibunching in the
photoluminescence from single carbon nanotubes. The emergence of a fast
luminescence decay component under strong optical excitation indicates that
Auger processes are partially responsible for inhibiting two-photon generation.
Additionally, the presence of exciton localization at low temperatures ensures
that nanotubes emit photons predominantly one by one. The fact that multiphoton
emission probability can be smaller than 5% suggests that carbon nanotubes
could be used as a source of single photons for applications in quantum
cryptography.Comment: content as publishe
Hunting Down the Best Model of Inflation with Bayesian Evidence
We present the first calculation of the Bayesian evidence for different
prototypical single field inflationary scenarios, including representative
classes of small field and large field models. This approach allows us to
compare inflationary models in a well-defined statistical way and to determine
the current "best model of inflation". The calculation is performed numerically
by interfacing the inflationary code FieldInf with MultiNest. We find that
small field models are currently preferred, while large field models having a
self-interacting potential of power p>4 are strongly disfavoured. The class of
small field models as a whole has posterior odds of approximately 3:1 when
compared with the large field class. The methodology and results presented in
this article are an additional step toward the construction of a full numerical
pipeline to constrain the physics of the early Universe with astrophysical
observations. More accurate data (such as the Planck data) and the techniques
introduced here should allow us to identify conclusively the best inflationary
model.Comment: 12 pages, 2 figures, uses RevTeX. Misprint corrected, references
added. Matches published versio
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