1,385 research outputs found
Quantum Quenches in Free Field Theory: Universal Scaling at Any Rate
Quantum quenches display universal scaling in several regimes. For quenches
which start from a gapped phase and cross a critical point, with a rate slow
compared to the initial gap, many systems obey Kibble-Zurek scaling. More
recently, a different scaling behaviour has been shown to occur when the quench
rate is fast compared to all other physical scales, but still slow compared to
the UV cutoff. We investigate the passage from fast to slow quenches in scalar
and fermionic free field theories with time dependent masses for which the
dynamics can be solved exactly for all quench rates. We find that renormalized
one point functions smoothly cross over between the regimes.Comment: 40 pages; v2: a bit late, but it includes minor modifications to
match published versio
Smooth and fast versus instantaneous quenches in quantum field theory
We examine in detail the relationship between smooth fast quantum quenches,
characterized by a time scale , and {\em instantaneous quenches},
within the framework of exactly solvable mass quenches in free scalar field
theory. Our earlier studies \cite{dgm1,dgm2} highlighted that the two protocols
remain distinct in the limit because of the relation
of the quench rate to the UV cut-off, i.e., always holds
in the fast smooth quenches while for instantaneous
quenches. Here we study UV finite quantities like correlators at finite spatial
distances and the excess energy produced above the final ground state energy.
We show that at late times and large distances (compared to the quench time
scale) the smooth quench correlator approaches that for the instantaneous
quench. At early times, we find that for small spatial separation and small
, the correlator scales universally with , exactly as in
the scaling of renormalized one point functions found in earlier work. At
larger separation, the dependence on drops out. The excess energy
density is finite (for finite ) and scales in a universal fashion
for all . However, the scaling behaviour produces a divergent result in the
limit for , just as in an instantaneous
quench, where it is UV divergent for . We argue that similar results
hold for arbitrary interacting theories: the excess energy density produced is
expected to diverge for scaling dimensions .Comment: 52 pages; v2: minor modifications to match published versio
An exactly solvable quench protocol for integrable spin models
Quantum quenches in continuum field theory across critical points are known
to display different scaling behaviours in different regimes of the quench
rate. We extend these results to integrable lattice models such as the
transverse field Ising model on a one-dimensional chain and the Kitaev model on
a two-dimensional honeycomb lattice using a nonlinear quench protocol which
allows for exact analytical solutions of the dynamics. Our quench protocol
starts with a finite mass gap at early times and crosses a critical point or a
critical region, and we study the behaviour of one point functions of the
quenched operator at the critical point or in the critical region as a function
of the quench rate. For quench rates slow compared to the initial mass gap, we
find the expected Kibble-Zurek scaling. In contrast, for rates fast compared to
the mass gap, but slow compared to the inverse lattice spacing, we find scaling
behaviour similar to smooth fast continuum quenches. For quench rates of the
same order of the lattice scale, the one point function saturates as a function
of the rate, approaching the results of an abrupt quench. The presence of an
extended critical surface in the Kitaev model leads to a variety of scaling
exponents depending on the starting point and on the time where the operator is
measured. We discuss the role of the amplitude of the quench in determining the
extent of the slow (Kibble-Zurek) and fast quench regimes, and the onset of the
saturation.Comment: 54 pages, 13 figures; v2: added analytic argument for Kitaev mode
Comments on Jacobson’s “entanglement equilibrium and the Einstein equation”
Using holographic calculations, we examine a key assumption made in Jacobson’s recent argument for deriving Einstein’s equations from vacuum entanglement entropy. Our results involving relevant operators with low conformal dimensions seem to conflict with Jacobson’s assumption. However, we discuss ways to circumvent this problem.Fil: Casini, Horacio German. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Galante, Damián A.. Western University; Canadá. Perimeter Institute for Theoretical Physics; CanadáFil: Myers, Robert C.. Perimeter Institute for Theoretical Physics; Canad
Deformed Special Relativity as an effective theory of measurements on quantum gravitational backgrounds
In this article we elaborate on a recently proposed interpretation of DSR as
an effective measurement theory in the presence of non-negligible (albeit
small) quantum gravitational fluctuations. We provide several heuristic
arguments to explain how such a new theory can emerge and discuss the possible
observational consequences of this framework.Comment: 11 pages, no figure
Importance of activity data for improving the residential wood combustion emission inventory at regional level
The contribution of residential wood combustion (RWC) to emission inventory at local level was estimated using a bottomeup approach for the Lombardy Region of North Italy. A survey, based on the CATI (Computer Assisted Telephone Interviewing) method, has been undertaken through 18,000 interviews. The interviews had the objective to characterize the RWC use in this region, in term of both total and municipal wood consumption. Details on the type of appliances used in RWC were also gathered. The results of the survey were then statistically analyzed in order to allow an estimate of RWC with high spatial resolution (i.e., at municipal level) in relation to the size and altitude of the territory. The work provides new evidence of the importance of wood combustion as a key source for PM and NMVOC emissions at local level, and thus highlights the importance of technological improvements and new policies aimed at emission reduction in this sector. Considering the great differences in average PM emission factors between low efficiency appliances (fireplaces, old stoves) and high efficiency ones (new stoves, pellet burners), this work emphasizes the importance of obtaining more detailed information on the types of wood appliances used for arriving at a reliable PM emission inventory for RWC
Search for radio halos in starburst galaxies
Starburst galaxies are undergoing intense episodes of star formation. In
these galaxies, gas is ejected into the surrounding environment through winds
created by the effect of hot stars and supernova explosions. When interacting
with the intergalactic medium, these winds can produce strong shocks capable of
accelerating cosmic rays. The radiation from these cosmic rays mainly occurs in
radio and gamma rays. The radio halo can be characterized using the scale
height. We searched for the presence of radio halos in a sample of edge-on
starburst galaxies gathered from the MeerKAT 1.28 GHz Atlas of Southern Sources
in the IRAS Revised Bright Galaxy Sample. We selected a sample of 25 edge-on
galaxies from the original sample and modeled their disk and halo
contributions. We have detected and characterized 11 radio halos, seven of
which are reported here for the first time. We found that the halo scale
heights increase linearly with the radio diameters and this relation does not
depend on the star formation rate. All galaxies in our sample follow the
radio-infrared relation with a q parameter value of . The dependence
of the halo luminosity on the star formation rate and the infrared luminosity
supports the hypothesis that the radio halos are the result of synchrotron
radiation produced by relativistic electrons and points toward the fact that
the star formation activity plays a crucial role in halo creation. The average
scale height of 1 kpc implies a dynamical range of 4 Myr, several orders of
magnitude greater than the synchrotron losses for electrons of 10 TeV. This
suggests that some process must exist to reaccelerate cosmic rays in the halo
if gamma-ray emission of a leptonic origin is detected from the halo. According
to the relation between the radio and gamma-ray luminosities, we found that NGC
4666 is a potential gamma-ray source for future observations.Comment: 21 pages, 5 tables, 8 figures. Accepted for publication in Astronomy
& Astrophysic
Modified Special Relativity on a fluctuating spacetime
It was recently proposed that deformations of the relativistic symmetry, as
those considered in Deformed Special Relativity (DSR), can be seen as the
outcome of a measurement theory in the presence of non-negligible (albeit
small) quantum gravitational fluctuations [1,2]. In this paper we explicitly
consider the case of a spacetime described by a flat metric endowed with
stochastic fluctuations and, for a free particle, we show that DSR-like
nonlinear relations between the spaces of the measured and classical momenta,
can result from the average of the stochastic fluctuations over a scale set be
the de Broglie wavelength of the particle. As illustrative examples we consider
explicitly the averaging procedure for some simple stochastic processes and
discuss the physical implications of our results.Comment: 7 pages, no figure
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