946 research outputs found
Revisiting the gauge fields of strained graphene
We show that, when graphene is only subject to strain, the spin connection
gauge field that arises plays no measurable role, but when intrinsic curvature
is present and strain is small, spin connection dictates most the physics. We
do so by showing that the Weyl field associated with strain is a pure gauge
field and no constraint on the -dimensional spacetime appears. On the
other hand, for constant intrinsic curvature that also gives a pure-gauge Weyl
field, we find a classical manifestation of a quantum Weyl anomaly, descending
from a constrained spacetime. We are in the position to do this because we find
the equations that the conformal factor in -dimensions has to satisfy,
that is a nontrivial generalization to -dimensions of the classic
Liouville equation of differential geometry of surfaces. Finally, we comment on
the peculiarities of the only gauge field that can describe strain, that is the
well known {\it pseudogauge field} and , and conclude by offering some scenarios of fundamental physics that
this peculiar field could help to realize.Comment: 24 pages, 6 figures. Comments added, text reduced and relevant
references include
Dynamical Contents of Unconventional Supersymmetry
The Dirac Hamiltonian formalism is applied to a system in -dimensions
consisting of a Dirac field minimally coupled to Chern-Simons and
connections, and , respectively. This theory is connected
to a supersymmetric Chern-Simons form in which the gravitino has been projected
out (unconventional supersymmetry) and, in the case of a flat background,
corresponds to the low energy limit of graphene. The separation between
first-class and second-class constraints is performed explicitly, and both the
field equations and gauge symmetries of the Lagrangian formalism are fully
recovered. The degrees of freedom of the theory in generic sectors shows that
the propagating states correspond to fermionic modes in the background
determined by the geometry of the graphene sheet and the nondynamical
electromagnetic field. This is shown for the following canonical sectors: i) a
conformally invariant generic description where the spinor field and the
dreibein are locally rescaled; ii) a specific configuration for the Dirac
fermion consistent with its spin, where Weyl symmetry is exchanged by time
reparametrizations; iii) the vacuum sector , which is of interest for
perturbation theory. For the latter the analysis is adapted to the case of
manifolds with boundary, and the corresponding Dirac brackets together with the
centrally extended charge algebra are found. Finally, the
generalization of the gauge group is briefly treated, yielding analogous
conclusions for the degrees of freedom.Comment: 17 pages. Accepted version for publication in JHE
Local supersymmetry without SUSY partners
A gauge theory for a superalgebra that includes an internal gauge (G) and
local Lorentz algebras, and that could describe the low energy particle
phenomenology is constructed. These two symmetries are connected by fermionic
supercharges. The system includes an internal gauge connection 1-form , a
spin-1/2 Dirac spinor , the Lorentz connection , and the vielbein
. The connection one-form is in the adjoint representation of G, while
is in the fundamental. In contrast to standard supergravity, the metric
is not a fundamental field and is in the center of the superalgebra: it is not
only invariant under the internal gauge group and under Lorentz
transformations, but is also invariant under supersymmetry. The features of
this theory that mark the difference with standard supersymmetry are: A) The
number of fermionic and bosonic states is not necessarily the same; B) There
are no superpartners with equal mass, "bosoninos", sleptons and squarks are
absent; C) Although this supersymmetry originates in a local gauge theory and
gravity is included, there is no gravitino; D) Fermions acquire mass from their
coupling to the background or from self-couplings, while bosons remain
massless. In odd dimensions, the Chern-Simons form provides an action that is
quasi-invariant under the entire superalgebra. In even dimensions, the
Yang-Mills form is the only natural option, and the symmetry breaks
down to [G x SO(1,D-1)]. In 4D, the construction follows the Townsend - Mac
Dowell-Mansouri approach. Due to the absence of osp(4|2)-invariant traces in
four dimensions, the resulting Lagrangian is only invariant under [U(1) x
SO(3,1)], and includes a Nambu--Jona-Lasinio term. In this case, the Lagrangian
depends on a single dimensionful parameter that fixes Newton's constant, the
cosmological constant and the NJL coupling.Comment: 24 pages, no figures. Title changed in journal version to
"Unconventional supersymmetry and its breaking". Few references added and
some paragraphs rewritten from v.1. This version includes two appendices that
are not found in the journal versio
Gribov gap equation at finite temperature
In this paper the Gribov gap equation at finite temperature is analyzed. The
solutions of the gap equation (which depend explicitly on the temperature)
determine the structure of the gluon propagator within the semi-classical
Gribov approach. The present analysis is consistent with the standard
confinement scenario for low temperatures, while for high enough temperatures,
deconfinement takes place and a free gluon propagator is obtained. It also
suggests the presence of the so-called semi-quark-gluon-plasma phase in between
the confined and quark-gluon plasma phases.Comment: 22 pages, 9 figures. Comments added, relevant references include
Canonical Field Anticommutators in the Extended Gauged Rarita-Schwinger Theory
We reexamine canonical quantization of the gauged Rarita-Schwinger theory
using the extended theory, incorporating a dimension auxiliary
spin- field , in which there is an exact off-shell gauge
invariance. In gauge, which reduces to the original unextended
theory, our results agree with those found by Johnson and Sudarshan, and later
verified by Velo and Zwanziger, which give a canonical Rarita-Schwinger field
Dirac bracket that is singular for small gauge fields. In gauge covariant
radiation gauge, the Dirac bracket of the Rarita-Schwinger fields is
nonsingular, but does not correspond to a positive semi-definite
anticommutator, and the Dirac bracket of the auxiliary fields has a singularity
of the same form as found in the unextended theory. These results indicate that
gauged Rarita-Schwinger theory is somewhat pathological, and cannot be
canonically quantized within a conventional positive semi-definite metric
Hilbert space. We leave open the questions of whether consistent quantizations
can be achieved by using an indefinite metric Hilbert space, by path integral
methods, or by appropriate couplings to conventional dimension
spin- fields.Comment: Latex, 17 page
Gauged WZW models for space-time groups and gravitational actions
In this paper we investigate gauged Wess-Zumino-Witten models for space-time
groups as gravitational theories, following the trend of recent work by
Anabalon, Willison and Zanelli. We discuss the field equations in any dimension
and study in detail the simplest case of two space-time dimensions and gauge
group SO(2,1). For this model we study black hole solutions and we calculate
their mass and entropy which resulted in a null value for both.Comment: 26 pages, no figure
Comments on the compatibility of thermodynamic equilibrium conditions with lattice propagators
In this paper the compatibility is analyzed of the non-perturbative equations
of state of quarks and gluons arising from the lattice with some natural
requirements for self-gravitating objects at equilibrium: the existence of an
equation of state (namely, the possibility to define the pressure as a function
of the energy density), the absence of superluminal propagation and Le
Chatelier's principle. It is discussed under which conditions it is possible to
extract an equation of state (in the above sense) from the non-perturbative
propagators arising from the fits of the latest lattice data. In the quark
case, there is a small but non-vanishing range of temperatures in which it is
not possible to define a single-valued functional relation between density and
pressure. Interestingly enough, a small change of the parameters appearing in
the fit of the lattice quark propagator (of around 10~\%) could guarantee the
fulfillment of all the three conditions (keeping alive, at the same time, the
violation of positivity of the spectral representation, which is the expected
signal of confinement). As far as gluons are concerned, the analysis shows very
similar results. Whether or not the non-perturbative quark and gluon
propagators satisfy these conditions can have a strong impact on the estimate
of the maximal mass of quark stars.Comment: 24 pages; 12 figures. Title slightly changed and improved discussion.
Version accepted for publication on European Physical Journal
Time-loops in Dirac materials, torsion and unconventional Supersymmetry
We propose a scenario where the effects of dislocations, in bidimensional
Dirac materials at low energies, can be described within a Dirac field theory
by a vertex proportional to the totally antisymmetric component of the torsion
generated by such dislocations. The well-known geometrical obstruction to have
a nonzero torsion term of that kind in this two-dimensional settings is
overcome through exotic time-loops, obtained from ingeniously manipulated
particle-hole dynamics. If such torsion/dislocation is indeed present, a net
flow of particles-antiparticles (holes) can be inferred and possibly measured.
Finally, we comment on how these discoveries pave the way to a laboratory
realization on Dirac materials of Unconventional Supersymmetry, as a top-down
description of the -electrons in backgrounds with a nonzero torsion.Comment: 6 pages, 2 Figures; contribution to the Proceedings of the 40th
International Conference on High Energy physics - ICHEP2020, July 28 - August
6, 2020, Prague, Czech Republic (virtual meeting
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