1,995 research outputs found
Mass generation for non-Abelian antisymmetric tensor fields in a three-dimensional space-time
Starting from a recently proposed Abelian topological model in (2+1)
dimensions, which involve the Kalb-Ramond two form field, we study a
non-Abelian generalization of the model. An obstruction for generalization is
detected. However we show that the goal is achieved if we introduce a vectorial
auxiliary field. Consequently, a model is proposed, exhibiting a non-Abelian
topological mass generation mechanism in D=3, that provides mass for the
Kalb-Ramond field. The covariant quantization of this model requires ghosts for
ghosts. Therefore in order to quantize the theory we construct a complete set
of BRST and anti-BRST equations using the horizontality condition.Comment: 8 pages. To appear in Physical Review
Local symmetries of the non-Abelian two-form
It is proposed that a non-Abelian adjoint two-form in BF type theories
transform inhomogeneously under the gauge group. The resulting restrictions on
invariant actions are discussed. The auxiliary one-form which is required for
maintaining vector gauge symmetry transforms like a second gauge field, and
hence cannot be fully absorbed in the two-form. But it can be replaced, via a
vector gauge transformation, by the usual gauge field, leading to gauge
equivalences between different types of theories. A new type of symmetry also
appears, one which depends on local functions but cannot be generated by
constraints. It is connected to the identity in the limit of a vanishing global
parameter, so it should be called a semiglobal symmetry. The corresponding
conserved currents and BRST charges are parametrized by the space of flat
connections.Comment: RevTeX4, 11 pages, minor correction
Gauge transformations of the non-Abelian two-form
A novel inhomogeneous gauge transformation law is proposed for a non-Abelian
adjoint two-form in four dimensions. Rules for constructing actions invariant
under this are given. The auxiliary vector field which appears in some of these
models transforms like a second connection in the theory. Another local
symmetry leaves the compensated three-form field strength invariant, but does
not seem to be generated by any combination of local constraints. Both types of
symmetries change the action by total divergences, suggesting that boundary
degrees of freedom have to be taken into account for local quantization.Comment: ReVTeX3.1, 4 page
Efficiency of a Brownian information machine
A Brownian information machine extracts work from a heat bath through a
feedback process that exploits the information acquired in a measurement. For
the paradigmatic case of a particle trapped in a harmonic potential, we
determine how power and efficiency for two variants of such a machine operating
cyclically depend on the cycle time and the precision of the positional
measurements. Controlling only the center of the trap leads to a machine that
has zero efficiency at maximum power whereas additional optimal control of the
stiffness of the trap leads to an efficiency bounded between 1/2, which holds
for maximum power, and 1 reached even for finite cycle time in the limit of
perfect measurements.Comment: 9 pages, 2 figure
Bailouts in a common market: a strategic approach
Governments in the EU grant Rescue and Restructure Subsidies to bail out ailing firms. In an international asymmetric Cournot duopoly we study effects of such subsidies on market structure and welfare. We adopt a common market setting, where consumers from the two countries form one market. We show that the subsidy is positive also when it fails to prevent the exit. The reason is a strategic effect, which forces the more efficient firm to make additional cost-reducing effort. When the exit is prevented, allocative and productive efficiencies are lower and the only gaining player is the rescued firm
Force-extension relation of cross-linked anisotropic polymer networks
Cross-linked polymer networks with orientational order constitute a wide
class of soft materials and are relevant to biological systems (e.g., F-actin
bundles). We analytically study the nonlinear force-extension relation of an
array of parallel-aligned, strongly stretched semiflexible polymers with random
cross-links. In the strong stretching limit, the effect of the cross-links is
purely entropic, independent of the bending rigidity of the chains. Cross-links
enhance the differential stretching stiffness of the bundle. For hard
cross-links, the cross-link contribution to the force-extension relation scales
inversely proportional to the force. Its dependence on the cross-link density,
close to the gelation transition, is the same as that of the shear modulus. The
qualitative behavior is captured by a toy model of two chains with a single
cross-link in the middle.Comment: 7 pages, 4 figure
New results on rewrite-based satisfiability procedures
Program analysis and verification require decision procedures to reason on
theories of data structures. Many problems can be reduced to the satisfiability
of sets of ground literals in theory T. If a sound and complete inference
system for first-order logic is guaranteed to terminate on T-satisfiability
problems, any theorem-proving strategy with that system and a fair search plan
is a T-satisfiability procedure. We prove termination of a rewrite-based
first-order engine on the theories of records, integer offsets, integer offsets
modulo and lists. We give a modularity theorem stating sufficient conditions
for termination on a combinations of theories, given termination on each. The
above theories, as well as others, satisfy these conditions. We introduce
several sets of benchmarks on these theories and their combinations, including
both parametric synthetic benchmarks to test scalability, and real-world
problems to test performances on huge sets of literals. We compare the
rewrite-based theorem prover E with the validity checkers CVC and CVC Lite.
Contrary to the folklore that a general-purpose prover cannot compete with
reasoners with built-in theories, the experiments are overall favorable to the
theorem prover, showing that not only the rewriting approach is elegant and
conceptually simple, but has important practical implications.Comment: To appear in the ACM Transactions on Computational Logic, 49 page
Lattice QCD at Imaginary Chemical Potential in the Chiral Limit
We report on an ongoing study on the interplay between Roberge-Weiss (RW) and
chiral transitions in simulations of (2+1)-flavor QCD with an imaginary
chemical potential. We established that the RW endpoint belongs to the 3-,
universality class when calculations are done with the Highly Improved
Staggered Quark (HISQ) action in the RW plane with physical quark masses. We
also have explored a range of quark masses corresponding to pion mass values,
~MeV and found that the transition is consistent with
universality class. We argue that observables that were usually used to
determine the chiral phase transition temperature, e.g. the chiral condensate
and chiral susceptibility, are sensitive to the RW transition and are
energy-like observables for the transition, contrary to the magnetic-like
(order parameter) behavior at vanishing chemical potential. Moreover the
calculations performed at ~MeV also put a stringent constraint for
a critical pion mass at zero chemical potential for a possible first-order
chiral phase transition.Comment: Prepared for the proceedings of LATTICE2021, MIT, USA, onlin
Speeding up the constraint-based method in difference logic
"The final publication is available at http://link.springer.com/chapter/10.1007%2F978-3-319-40970-2_18"Over the years the constraint-based method has been successfully applied to a wide range of problems in program analysis, from invariant generation to termination and non-termination proving. Quite often the semantics of the program under study as well as the properties to be generated belong to difference logic, i.e., the fragment of linear arithmetic where atoms are inequalities of the form u v = k. However, so far constraint-based techniques have not exploited this fact: in general, Farkas’ Lemma is used to produce the constraints over template unknowns, which leads to non-linear SMT problems. Based on classical results of graph theory, in this paper we propose new encodings for generating these constraints when program semantics and templates belong to difference logic. Thanks to this approach, instead of a heavyweight non-linear arithmetic solver, a much cheaper SMT solver for difference logic or linear integer arithmetic can be employed for solving the resulting constraints. We present encouraging experimental results that show the high impact of the proposed techniques on the performance of the VeryMax verification systemPeer ReviewedPostprint (author's final draft
Are Steadily Moving Crystals Unstable?
We study the dynamics of small fluctuations about the uniform state of a
crystal moving through a dissipative medium, e.g. a sedimenting colloidal
crystal or a moving flux lattice, using a set of continuum equations for the
displacement fields, and a one-dimensional driven lattice-gas model for the
coupled concentration and tilt fields. For the colloidal crystal we predict a
continuous nonequilibrium phase transition to a clumped state above a critical
Peclet number.Comment: 4 pages, revtex, 2 .eps figures, uses epsf.sty; To be published in
Phys. Rev. Lett. This version is substantially rewritten but the essential
content is the same as befor
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