35 research outputs found
Faddeev-Niemi Conjecture and Effective Action of QCD
We calculate a one loop effective action of SU(2) QCD in the presence of the
monopole background, and find a possible connection between the resulting QCD
effective action and a generalized Skyrme-Faddeev action of the non-linear
sigma model. The result is obtained using the gauge-independent decomposotion
of the gauge potential into the topological degrees which describes the
non-Abelian monopoles and the local dynamical degrees of the potential, and
integrating out all the dynamical degrees of QCD.Comment: 6 page
The effective action and quantum gauge transformations
The local symmetry transformations of the quantum effective action for
general gauge theory are found. Additional symmetries arise under consideration
of background gauges. Together with "trivial" gauge transformations, vanishing
on mass shell, they can be used for construction simple gauge generators. For
example, for the Yang-Mills theory the classically invariant effective action
is obtained, reproducing DeWitt's result. For rank one theories a natural
generalization is proposed.Comment: Revtex, 11 pages; added reference
Inflation with a Weyl term, or ghosts at work
In order to assess the role of ghosts in cosmology, we study the evolution of
linear cosmological perturbations during inflation when a Weyl term is added to
the action. Our main result is that vector perturbations can no longer be
ignored and that scalar modes diverge in the newtonian gauge but remain bounded
in the comoving slicing.Comment: 14 pages, 4 figure
On the Background Field Method Beyond One Loop: A manifestly covariant derivative expansion in super Yang-Mills theories
There are currently many string inspired conjectures about the structure of
the low-energy effective action for super Yang-Mills theories which require
explicit multi-loop calculations. In this paper, we develop a manifestly
covariant derivative expansion of superspace heat kernels and present a scheme
to evaluate multi-loop contributions to the effective action in the framework
of the background field method. The crucial ingredient of the construction is a
detailed analysis of the properties of the parallel displacement propagators
associated with Yang-Mills supermultiples in N-extended superspace.Comment: 32 pages, latex, 7 EPS figures. v2: references, comments added, typos
corrected, incorrect `skeleton' conjecture in sect. 3 replaced by a more
careful treatment. v3: typos corrected, final version published in JHE
Method to compute the stress-energy tensor for the massless spin 1/2 field in a general static spherically symmetric spacetime
A method for computing the stress-energy tensor for the quantized, massless,
spin 1/2 field in a general static spherically symmetric spacetime is
presented. The field can be in a zero temperature state or a non-zero
temperature thermal state. An expression for the full renormalized
stress-energy tensor is derived. It consists of a sum of two tensors both of
which are conserved. One tensor is written in terms of the modes of the
quantized field and has zero trace. In most cases it must be computed
numerically. The other tensor does not explicitly depend on the modes and has a
trace equal to the trace anomaly. It can be used as an analytic approximation
for the stress-energy tensor and is equivalent to other approximations that
have been made for the stress-energy tensor of the massless spin 1/2 field in
static spherically symmetric spacetimes.Comment: 34 pages, no figure
Shape Space Methods for Quantum Cosmological Triangleland
With toy modelling of conceptual aspects of quantum cosmology and the problem
of time in quantum gravity in mind, I study the classical and quantum dynamics
of the pure-shape (i.e. scale-free) triangle formed by 3 particles in 2-d. I do
so by importing techniques to the triangle model from the corresponding 4
particles in 1-d model, using the fact that both have 2-spheres for shape
spaces, though the latter has a trivial realization whilst the former has a
more involved Hopf (or Dragt) type realization. I furthermore interpret the
ensuing Dragt-type coordinates as shape quantities: a measure of
anisoscelesness, the ellipticity of the base and apex's moments of inertia, and
a quantity proportional to the area of the triangle. I promote these quantities
at the quantum level to operators whose expectation and spread are then useful
in understanding the quantum states of the system. Additionally, I tessellate
the 2-sphere by its physical interpretation as the shape space of triangles,
and then use this as a back-cloth from which to read off the interpretation of
dynamical trajectories, potentials and wavefunctions. I include applications to
timeless approaches to the problem of time and to the role of uniform states in
quantum cosmological modelling.Comment: A shorter version, as per the first stage in the refereeing process,
and containing some new reference
On the Particle Definition in the presence of Black Holes
A canonical particle definition via the diagonalisation of the Hamiltonian
for a quantum field theory in specific curved space-times is presented. Within
the provided approach radial ingoing or outgoing Minkowski particles do not
exist. An application of this formalism to the Rindler metric recovers the
well-known Unruh effect. For the situation of a black hole the Hamiltonian
splits up into two independent parts accounting for the interior and the
exterior domain, respectively. It turns out that a reasonable particle
definition may be accomplished for the outside region only. The Hamiltonian of
the field inside the black hole is unbounded from above and below and hence
possesses no ground state. The corresponding equation of motion displays a
linear global instability. Possible consequences of this instability are
discussed and its relations to the sonic analogues of black holes are
addressed. PACS-numbers: 04.70.Dy, 04.62.+v, 10.10.Ef, 03.65.Db.Comment: 44 pages, LaTeX, no figures, accepted for publication in Phys. Rev.
The BES f_0(1810): a new glueball candidate
We analyze the f_0(1810) state recently observed by the BES collaboration via
radiative J/\psi decay to a resonant \phi\omega spectrum and confront it with
DM2 data and glueball theory. The DM2 group only measured \omega\omega decays
and reported a pseudoscalar but no scalar resonance in this mass region. A
rescattering mechanism from the open flavored KKbar decay channel is considered
to explain why the resonance is only seen in the flavor asymmetric \omega\phi
branch along with a discussion of positive C parity charmonia decays to
strengthen the case for preferred open flavor glueball decays. We also
calculate the total glueball decay width to be roughly 100 MeV, in agreement
with the narrow, newly found f_0, and smaller than the expected estimate of
200-400 MeV. We conclude that this discovered scalar hadron is a solid glueball
candidate and deserves further experimental investigation, especially in the
K-Kbar channel. Finally we comment on other, but less likely, possible
assignments for this state.Comment: 11 pages, 4 figures. Major substantive additions, including an
ab-initio, QCD-based computation of the glueball inclusive decay width,
evaluation of final state effects, and enhanced discussion of several
alternative possibilities. Our conclusions are unchanged: the BES f_0(1810)
is a promising glueball candidat
North Tropical Atlantic influence on western Amazon fire season variability
The prevailing wet climate in the western Amazon is not favorable to the natural occurrence of fires. Nevertheless, the current process of clearing of humid forests for agriculture and cattle ranching has increased the vulnerability of the region to the spread of fires. Using meteorological stations precipitation and the Moderate Resolution Spectroradiometer (MODIS) Active-Fires (AF) during 2000-2009, we show that fire anomalies vary closely with July-August-September (JAS) precipitation variability as measured by the Standardized Precipitation Index (SPI). The precipitation variability is, in turn, greatly determined by sea surface temperature (SST) anomalies in the North Tropical Atlantic (NTA). We develop a linear regression model to relate local fire activity to an index of the NTA-SST. By using seasonal forecasts of SST from a coupled model, we are able to predict anomalous JAS fire activity as early as April. We applied the method to predict the severe 2010 JAS season, which indicated strongly positive seasonal fire anomalies within the 95% prediction confidence intervals in most western Amazon. The spatial distribution of predicted SPI was also in accordance with observed precipitation anomalies. This three months lead time precipitation and fire prediction product in the western Amazon could help local decision makers to establish an early warning systems or other appropriate course of action before the fire season begins
Casimir Effect, Achucarro-Ortiz Black Hole and the Cosmological Constant
We treat the two-dimensional Achucarro-Ortiz black hole (also known as (1+1)
dilatonic black hole) as a Casimir-type system. The stress tensor of a massless
scalar field satisfying Dirichlet boundary conditions on two one-dimensional
"walls" ("Dirichlet walls") is explicitly calculated in three different vacua.
Without employing known regularization techniques, the expression in each
vacuum for the stress tensor is reached by using the Wald's axioms. Finally,
within this asymptotically non-flat gravitational background, it is shown that
the equilibrium of the configurations, obtained by setting Casimir force to
zero, is controlled by the cosmological constant.Comment: 20 pages, LaTeX, minor corrections, comments and clarifications
added, version to appear in Phys. Rev.