1,479 research outputs found
Massless fermions in a bag at finite density and temperature
We introduce the chemical potential in a system of massless fermions in a bag
by impossing boundary conditions in the Euclidean time direction. We express
the fermionic mean number in terms of a functional trace involving the Green's
function of the boundary value problem, which we study analytically. Numerical
evaluations are made, and an application to a simple hadron model is discussed.Comment: 14 pages, 3 figures, RevTe
On the relation between local and geometric Lagrangians for higher spins
Equations of motion for free higher-spin gauge fields of any symmetry can be
formulated in terms of linearised curvatures. On the other hand, gauge
invariance alone does not fix the form of the corresponding actions which, in
addition, either contain higher derivatives or involve inverse powers of the
d'Alembertian operator, thus introducing possible subtleties in degrees of
freedom count. We suggest a path to avoid ambiguities, starting from local,
unconstrained Lagrangians previously proposed, and integrating out the
auxiliary fields from the functional integral, thus generating a unique
non-local theory expressed in terms of curvatures.Comment: 14 pages. Contribution to the proceedings of the 1st Mediterranean
Conference on Classical and Quantum Gravity, Kolymbary (Crete, Greece)
September 14-18 200
Maxwell-like Lagrangians for higher spins
We show how implementing invariance under divergence-free gauge
transformations leads to a remarkably simple Lagrangian description of massless
bosons of any spin. Our construction covers both flat and (A)dS backgrounds and
extends to tensors of arbitrary mixed-symmetry type. Irreducible and traceless
fields produce single-particle actions, while whenever trace constraints can be
dispensed with the resulting Lagrangians display the same reducible,
multi-particle spectra as those emerging from the tensionless limit of free
open-string field theory. For all explored options the corresponding kinetic
operators take essentially the same form as in the spin-one, Maxwell case.Comment: 77 pages, revised version. Erroneous interpretation and proof of the
gauge-fixing procedure for mixed-symmetry fields corrected. As a consequence,
the mixed-symmetry, one-particle Lagrangians are to be complemented with
conditions on the divergences of the fields; all other conclusions unchanged.
Additional minor changes including references added. To appear in JHE
Asymptotic symmetries and charges at null infinity: from low to high spins
Weinberg's celebrated factorisation theorem holds for soft quanta of
arbitrary integer spin. The same result, for spin one and two, has been
rederived assuming that the infinite-dimensional asymptotic symmetry group of
Maxwell's equations and of asymptotically flat spaces leave the S-matrix
invariant. For higher spins, on the other hand, no such infinite-dimensional
asymptotic symmetries were known and, correspondingly, no a priori derivation
of Weinberg's theorem could be conjectured. In this contribution we review the
identification of higher-spin supertranslations and superrotations in as
well as their connection to Weinberg's result. While the procedure we follow
can be shown to be consistent in any , no infinite-dimensional enhancement
of the asymptotic symmetry group emerges from it in , thus leaving a
number of questions unanswered.Comment: 11 pages. Contribution to the proceedings of Quarks-2018, XXth
International Seminar on High Energy Physics; Valday, Russia, 27 May - 2 June
201
Tensor gauge fields in arbitrary representations of GL(D,R): II. Quadratic actions
Quadratic, second-order, non-local actions for tensor gauge fields
transforming in arbitrary irreducible representations of the general linear
group in D-dimensional Minkowski space are explicitly written in a compact form
by making use of Levi-Civita tensors. The field equations derived from these
actions ensure the propagation of the correct massless physical degrees of
freedom and are shown to be equivalent to non-Lagrangian local field equations
proposed previously. Moreover, these actions allow a frame-like reformulation a
la MacDowell-Mansouri, without any trace constraint in the tangent indices.Comment: LaTeX, 53 pages, no figure. Accepted for publication in
Communications in Mathematical Physics. Local Fierz-Pauli programme achieved
by completing the analysis of Labastid
Cost-based Optimization of Multistore Query Plans
Multistores are data management systems that enable query processing across different and heterogeneous databases; besides the distribution of data, complexity factors like schema heterogeneity and data replication must be resolved through integration and data fusion activities. Our multistore solution relies on a dataspace to provide the user with an integrated view of the available data and enables the formulation and execution of GPSJ queries. In this paper, we propose a technique to optimize the execution of GPSJ queries by formulating and evaluating different execution plans on the multistore. In particular, we outline different strategies to carry out joins and data fusion by relying on different schema representations; then, a self-learning black-box cost model is used to estimate execution times and select the most efficient plan. The experiments assess the effectiveness of the cost model in choosing the best execution plan for the given queries and exploit multiple multistore benchmarks to investigate the factors that influence the performance of different plans
Effective action in a higher-spin background
We consider a free massless scalar field coupled to an infinite tower of
background higher-spin gauge fields via minimal coupling to the traceless
conserved currents. The set of Abelian gauge transformations is deformed to the
non-Abelian group of unitary operators acting on the scalar field. The gauge
invariant effective action is computed perturbatively in the external fields.
The structure of the various (divergent or finite) terms is determined. In
particular, the quadratic part of the logarithmically divergent (or of the
finite) term is expressed in terms of curvatures and related to conformal
higher-spin gravity. The generalized higher-spin Weyl anomalies are also
determined. The relation with the theory of interacting higher-spin gauge
fields on anti de Sitter spacetime via the holographic correspondence is
discussed.Comment: 40 pages, Some errors and typos corrected, Version published in JHE
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