1,604 research outputs found
Dielectric function and plasmons of doped three-dimensional Luttinger semimetals
Luttinger semimetals are three-dimensional electron systems with a parabolic
band touching and an effective total spin . In this paper, we present an
analytical theory of dielectric screening of inversion-symmetric Luttinger
semimetals with an arbitrary carrier density and conduction-valence effective
mass asymmetry. Assuming a spherical approximation for the single-particle
Luttinger Hamiltonian, we determine analytically the dielectric screening
function in the random phase approximation for arbitrary values of the wave
vector and frequency, the latter in the complex plane. We use this analytical
expression to calculate the dispersion relation and Landau damping of the
collective modes in the charge sector (i.e., plasmons).Comment: 17 pages, 5 figures, published versio
ABJM -Bremsstrahlung at four loops and beyond: non-planar corrections
We consider the Bremsstrahlung function associated to a 1/6-BPS Wilson loop
in ABJM theory, with a cusp in the couplings to scalar fields. We non-trivially
extend its recent four-loop computation at weak coupling to include non-planar
corrections. We have recently proposed a conjecture relating this object to
supersymmetric circular Wilson loops with multiple windings, which can be
computed via localization. We find agreement between this proposal and the
perturbative computation of the Bremsstrahlung function, including color
sub-leading corrections. This supports the conjecture and hints at its validity
beyond the planar approximation.Comment: 22 page
ABJM -Bremsstrahlung at four loops and beyond
In ABJ(M) theory a generalized cusp can be constructed out of the 1/6 BPS
Wilson line by introducing an angle in the spacial contour and/or an
angle in the internal R-symmetry space. The small angles limits of its
anomalous dimension are controlled by corresponding Bremsstrahlung functions.
In this note we compute the internal space -Bremsstrahlung function to
four loops at weak coupling in the planar limit. Based on this result, we
propose an all order conjecture for the -Bremsstrahlung function.Comment: 40 pages; v2: references added, JHEP published extended versio
Parallel Implementation of Efficient Search Schemes for the Inference of Cancer Progression Models
The emergence and development of cancer is a consequence of the accumulation
over time of genomic mutations involving a specific set of genes, which
provides the cancer clones with a functional selective advantage. In this work,
we model the order of accumulation of such mutations during the progression,
which eventually leads to the disease, by means of probabilistic graphic
models, i.e., Bayesian Networks (BNs). We investigate how to perform the task
of learning the structure of such BNs, according to experimental evidence,
adopting a global optimization meta-heuristics. In particular, in this work we
rely on Genetic Algorithms, and to strongly reduce the execution time of the
inference -- which can also involve multiple repetitions to collect
statistically significant assessments of the data -- we distribute the
calculations using both multi-threading and a multi-node architecture. The
results show that our approach is characterized by good accuracy and
specificity; we also demonstrate its feasibility, thanks to a 84x reduction of
the overall execution time with respect to a traditional sequential
implementation
String theory duals of Wilson loops from Higgsing
For three-dimensional ABJ(M) theories and Chern-Simons-matter
quiver theories, we construct two sets of 1/2 BPS Wilson loop operators by
applying the Higgsing procedure along independent directions of the moduli
space, and choosing different massive modes. For theories whose dual M-theory
description is known, we also determine the corresponding spectrum of 1/2 BPS
M2-brane solutions. We identify the supercharges in M-theory and field theory,
as well as the supercharges preserved by M2-/anti-M2-branes and 1/2 BPS Wilson
loops. In particular, in orbifold ABJM theory we find pairs of
different 1/2 BPS Wilson loops that preserve exactly the same set of
supercharges. In field theory they arise by Higgsing with the choice of either
particles or antiparticles, whereas in the dual description they correspond to
a pair of M2-/anti-M2-branes localized at different positions in the compact
space. This result enlightens the origin of classical Wilson loop degeneracy in
these theories, already discussed in arXiv:1506.07614. A discussion on possible
scenarios that emerge by comparison with localization results is included.Comment: 52 pages, 4 figures; V2, 61 pages, 4 figures, supercharges in gravity
and field theory identified, conclusion unchanged, published versio
A new tri-generation system: thermodynamical analysis of a micro compressed air energy storage
There is a growing interest in the electrical energy storage system, especially for matching intermittent sources of renewable
energy with customers’ demand. Furthermore, it is possible, with these system, to level the absorption peak of the electric network
(peak shaving) and the advantage of separating the production phase from the exertion phase (time shift). CAES (compressed air
energy storage systems) are one of the most promising technologies of this field, because they are characterized by a high reliability,
low environmental impact and a remarkable energy density. The main disadvantage of big systems is that they depend on geological
formations which are necessary to the storage. The micro-CAES system, with a rigid storage vessel, guarantees a high portability of the
system and a higher adaptability even with distributed or stand-alone energy productions. This article carries out a thermodynamical
and energy analysis of the micro-CAES system, as a result of the mathematical model created in a Matlab/Simulink® environment.
New ideas will be discussed, as the one concerning the quasi-isothermal compression/expansion, through the exertion of a biphasic
mixture, that will increase the total system efficiency and enable a combined production of electric, thermal and refrigeration energies.
The exergy analysis of the results provided by the simulation of the model reports that more than one third of the exergy input to the
system is lost. This is something promising for the development of an experimental device
A matrix model for the latitude Wilson loop in ABJM theory
In ABJ(M) theory, we propose a matrix model for the exact evaluation of BPS
Wilson loops on a latitude circular contour, so providing a new weak-strong
interpolation tool. Intriguingly, the matrix model turns out to be a particular
case of that computing torus knot invariants in Chern-Simons
theory. At weak coupling we check our proposal against a three-loop
computation, performed for generic framing, winding number and representation.
The matrix model is amenable of a Fermi gas formulation, which we use to
systematically compute the strong coupling and genus expansions. For the
fermionic Wilson loop the leading planar behavior agrees with a previous string
theory prediction. For the bosonic operator our result provides a clue for
finding the corresponding string dual configuration. Our matrix model is
consistent with recent proposals for computing Bremsstrahlung functions exactly
in terms of latitude Wilson loops. As a by-product, we extend the conjecture
for the exact Bremsstrahlung function to generic
representations and test it with a four-loop perturbative computation. Finally,
we propose an exact prediction for at unequal gauge group ranks.Comment: 73 pages; v2: several improvements, JHEP published versio
Towards the exact Bremsstrahlung function of ABJM theory
We present the three-loop calculation of the Bremsstrahlung function
associated to the 1/2-BPS cusp in ABJM theory, including color subleading
corrections. Using the BPS condition we reduce the computation to that of a
cusp with vanishing angle. We work within the framework of heavy quark
effective theory (HQET) that further simplifies the analytic evaluation of the
relevant cusp anomalous dimension in the near-BPS limit. The result passes
nontrivial tests, such as exponentiation, and is in agreement with the
conjecture made in [1] for the exact expression of the Bremsstrahlung function,
based on the relation with fermionic latitude Wilson loops.Comment: 46 pages, 15 figure
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