89 research outputs found
Vacuum structure of CP^N sigma models at theta=pi
We show that parity symmetry is not spontaneously broken in the CP^N sigma
model for any value of N when the coefficient of the --term becomes
(mod ). The result follows from a non-perturbative analysis
of the nodal structure of the vacuum functional . The dynamical role
of sphalerons turns out to be very important for the argument. The result
introduces severe constraints on the possible critical behavior of the models
at (mod ).Comment: 8 pages, revtex, to appear in Phys. Rev. Let
Yang-Mills Theory as a Deformation of Topological Field Theory, Dimensional Reduction and Quark Confinement
We propose a reformulation of Yang-Mills theory as a perturbative deformation
of a novel topological (quantum) field theory. We prove that this reformulation
of the four-dimensional QCD leads to quark confinement in the sense of area law
of the Wilson loop. First, Yang-Mills theory with a non-Abelian gauge group G
is reformulated as a deformation of a novel topological field theory. Next, a
special class of topological field theories is defined by both BRST and
anti-BRST exact action corresponding to the maximal Abelian gauge leaving the
maximal torus group H of G invariant. Then we find the topological field theory
() has a hidden supersymmetry for a choice of maximal Abelian gauge. As a
result, the D-dimensional topological field theory is equivalent to the
(D-2)-dimensional coset G/H non-linear sigma model in the sense of Parisi and
Sourlas dimensional reduction. After maximal Abelian gauge fixing, the
topological property of magnetic monopole and anti-monopole of four-dimensional
Yang-Mills theory is translated into that of instanton and anti-instanton in
two-dimensional equivalent model. It is shown that the linear static potential
in four-dimensions follows from the instanton--anti-instanton gas in the
equivalent two-dimensional non-linear sigma model obtained from the
four-dimensional topological field theory by dimensional reduction, while the
remaining Coulomb potential comes from the perturbative part in
four-dimensional Yang-Mills theory. The dimensional reduction opens a path for
applying various exact methods developed in two-dimensional quantum field
theory to study the non-perturbative problem in low-energy physics of
four-dimensional quantum field theories.Comment: 58 pages, Latex, no figures, version accepted for publication in
Phys. Rev. D (additions of Discussion, references and minor changes
Large-order NSPT for lattice gauge theories with fermions:the plaquette in massless QCD
Numerical Stochastic Perturbation Theory (NSPT) allows for perturbative
computations in quantum field theory. We present an implementation of NSPT that
yields results for high orders in the perturbative expansion of lattice gauge
theories coupled to fermions. The zero-momentum mode is removed by imposing
twisted boundary conditions; in turn, twisted boundary conditions require us to
introduce a smell degree of freedom in order to include fermions in the
fundamental representation. As a first application, we compute the critical
mass of two flavours of Wilson fermions up to order in a
gauge theory. We also implement, for the first time,
staggered fermions in NSPT. The residual chiral symmetry of staggered fermions
protects the theory from an additive mass renormalisation. We compute the
perturbative expansion of the plaquette with two flavours of massless staggered
fermions up to order in a gauge theory, and
investigate the renormalon behaviour of such series. We are able to subtract
the power divergence in the Operator Product Expansion (OPE) for the plaquette
and estimate the gluon condensate in massless QCD. Our results confirm that
NSPT provides a viable way to probe systematically the asymptotic behaviour of
perturbative series in QCD and, eventually, gauge theories with fermions in
higher representations.Comment: 49 pages, 28 figures. Revised version, to be published in EPJC. Some
references added, typos corrected, and improved discussion on finite-volume
effect
The Relative Impact of 15-Minutes of Meditation Compared to a Day of Vacation in Daily Life: An Exploratory Analysis
Meditation and vacation are often perceived as activities that promote well-being and relieve stress. While clearly distinct, the extent to which meditation and vacation indeed have similar effects in daily life is an open question. We examined this question with beginning meditators in an eight-week A-B-A-B experimental protocol (A = not meditating; B = meditating). Community citizens and psychology students filled out daily surveys of affect and mindfulness and reported when they meditated or took vacation. On meditation days, participants reported lower levels of negative affect and higher levels of wellbeing, positive affect, and the mindfulness facets of observing sensations, describing thoughts and emotions, and nonreacting to feelings. We found similar associations of vacation with observing and nonreacting, and larger effects for well-being, positive affect, and negative affect. These results indicate that beginning meditation and vacation may indeed have overlapping effects, providing multiple pathways to boosts in well-being and mindfulness
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