898 research outputs found
Galilean symmetry in the effective theory of inflation: new shapes of non-Gaussianity
We study the consequences of imposing an approximate Galilean symmetry on the
Effective Theory of Inflation, the theory of small perturbations around the
inflationary background. This approach allows us to study the effect of
operators with two derivatives on each field, which can be the leading
interactions due to non-renormalization properties of the Galilean Lagrangian.
In this case cubic non-Gaussianities are given by three independent operators,
containing up to six derivatives, two with a shape close to equilateral and one
peaking on flattened isosceles triangles. The four-point function is larger
than in models with small speed of sound and potentially observable with the
Planck satellite.Comment: 23 pages, 6 figures. v2: minor changes to match JCAP published
versio
(Small) Resonant non-Gaussianities: Signatures of a Discrete Shift Symmetry in the Effective Field Theory of Inflation
We apply the Effective Field Theory of Inflation to study the case where the
continuous shift symmetry of the Goldstone boson \pi is softly broken to a
discrete subgroup. This case includes and generalizes recently proposed String
Theory inspired models of Inflation based on Axion Monodromy. The models we
study have the property that the 2-point function oscillates as a function of
the wavenumber, leading to oscillations in the CMB power spectrum. The
non-linear realization of time diffeomorphisms induces some self-interactions
for the Goldstone boson that lead to a peculiar non-Gaussianity whose shape
oscillates as a function of the wavenumber. We find that in the regime of
validity of the effective theory, the oscillatory signal contained in the
n-point correlation functions, with n>2, is smaller than the one contained in
the 2-point function, implying that the signature of oscillations, if ever
detected, will be easier to find first in the 2-point function, and only then
in the higher order correlation functions. Still the signal contained in
higher-order correlation functions, that we study here in generality, could be
detected at a subleading level, providing a very compelling consistency check
for an approximate discrete shift symmetry being realized during inflation.Comment: v2 minor revisions; 39 pages, 5 figure
TG, FT-IR and NMR characterization of n-C16H34 contaminated alumina and silica after mechanochemical treatment
This paper deals with the application of mechanochemistry to model systems composed of alumina or silica artificially contaminated with n-C16H34. The mechanochemical treatment was carried out by means of a ring mill for times ranging from 10 to 40 h. Thermogravimetry and infrared and nuclear magnetic resonance spectroscopies were used for the characterization of the mechanochemical products. The results have indicated that, in the case of alumina, almost all the contaminant n-C16H34 undergoes a complex oxidative reaction path whose end products are strongly held on the surface. These end products are most likely made of crosslinked, partially oxidized hydrocarbon chains bond to the solid surface via COO− groups. In the case of silica, the hydrocarbon undergoes a different, equally complex reaction path, but to a lower extent. In this case the end products are most probably carbonylic compounds and graphitic carbon. Then, for both solid matrices, the mechanochemical treatment promotes significant modification of the chemical nature of the polluting hydrocarbon with end products much more difficult to remove from the surface. As the systems studied are models of sites contaminated by aliphatic hydrocarbon, the results are worthy of consideration in relation to the mobility of the contaminants in the environment
Scale-Invariance and the Strong Coupling Problem
The effective theory of adiabatic fluctuations around arbitrary
Friedmann-Robertson-Walker backgrounds - both expanding and contracting -
allows for more than one way to obtain scale-invariant two-point correlations.
However, as we show in this paper, it is challenging to produce scale-invariant
fluctuations that are weakly coupled over the range of wavelengths accessible
to cosmological observations. In particular, requiring the background to be a
dynamical attractor, the curvature fluctuations are scale-invariant and weakly
coupled for at least 10 e-folds only if the background is close to de Sitter
space. In this case, the time-translation invariance of the background
guarantees time-independent n-point functions. For non-attractor solutions, any
predictions depend on assumptions about the evolution of the background even
when the perturbations are outside of the horizon. For the simplest such
scenario we identify the regions of the parameter space that avoid both
classical and quantum mechanical strong coupling problems. Finally, we present
extensions of our results to backgrounds in which higher-derivative terms play
a significant role.Comment: 17 pages + appendices, 3 figures; v2: typos fixe
Public Good Provision with Convex Costs
This paper considers a model of voluntary public good provision with two players and convex costs. I demonstrate that the provision of public good is higher in the sequential framework under fairly general conditions. This outcome shows that introducing convex costs may reverse under some condition the results of Varian ( 1994)
Public Good Provision with Convex Costs
This paper considers a model of voluntary public good provision with two players and convex costs. I demonstrate that the provision of public good is higher in the sequential framework under fairly general conditions. This outcome shows that introducing convex costs may reverse under some condition the results of Varian ( 1994)
Correlation effects in quasi one dimensional electron wires
We explore the role of electron correlation in quasi one dimensional quantum
wires as the range of the interaction potential is changed and their thickness
is varied by performing exact quantum Monte Carlo simulations at various
electronic densities. In the case of unscreened interactions with a long range
1/x tail there is a crossover from a liquid to a quasi Wigner crystal state as
the density decreases. When this interaction is screened, quasi long range
order is prevented from forming, although a significant correlation with 4 k_F
periodicity is still present at low densities. At even lower electron
concentration, exchange is suppressed and the spin-dependent interactions
become negligible, making the electrons behave like spinless fermions. We show
that this behavior is shared by the long range and screened interactions by
studying the spin and charge excitations of the system in both cases. Finally,
we study the effect of electron correlations in the double quantum wire
experiment [Steinberg et al., Phys. Rev. B 77, 113307 (2006)], by introducing
an accurate model for the screening in the experiment and explicitly including
the finite length of the system in our simulations. We find that decreasing the
electron density drives the system from a liquid to a state with quite strong 4
k_F correlations. This crossover takes place around , the
density where the electron localization occurs in the experiment. The charge
and spin velocities are also in remarkable agreement with the experimental
findings in the proximity of the crossover. We argue that correlation effects
play an important role at the onset of the localization transition.Comment: minor improvements, 13 pages, 12 figure
Homologation chemistry with nucleophilic α-substituted organometallic reagents: Chemocontrol, new concepts and (solved) challenges
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