946 research outputs found

    Revisiting the gauge fields of strained graphene

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    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 (2+1)(2+1)-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 (2+1)(2+1)-dimensions has to satisfy, that is a nontrivial generalization to (2+1)(2+1)-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} A1∼u11−u22A_1 \sim u_{11} - u_{22} and A2∼u12A_2 \sim u_{12}, 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

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    The Dirac Hamiltonian formalism is applied to a system in (2+1)(2+1)-dimensions consisting of a Dirac field ψ\psi minimally coupled to Chern-Simons U(1)U(1) and SO(2,1)SO(2,1) connections, AA and ω\omega, 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 ψ=0\psi=0, 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 SU(2)SU(2) 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

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    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 AA, a spin-1/2 Dirac spinor ψ\psi, the Lorentz connection ω\omega, and the vielbein ee. The connection one-form is in the adjoint representation of G, while ψ\psi 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

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    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

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    We reexamine canonical quantization of the gauged Rarita-Schwinger theory using the extended theory, incorporating a dimension 12\frac{1}{2} auxiliary spin-12\frac{1}{2} field Λ\Lambda, in which there is an exact off-shell gauge invariance. In Λ=0\Lambda=0 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 32\frac{3}{2} spin-12\frac{1}{2} fields.Comment: Latex, 17 page

    Gauged WZW models for space-time groups and gravitational actions

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    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

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    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

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    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 π\pi-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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