249 research outputs found
Lattice gauge theory with baryons at strong coupling
We study the effective Hamiltonian for strong-coupling lattice QCD in the
case of non-zero baryon density. In leading order the effective Hamiltonian is
a generalized antiferromagnet. For naive fermions, the symmetry is U(4N_f) and
the spins belong to a representation that depends on the local baryon number.
Next-nearest-neighbor (nnn) terms in the Hamiltonian break the symmetry to
U(N_f) x U(N_f). We transform the quantum problem to a Euclidean sigma model
which we analyze in a 1/N_c expansion. In the vacuum sector we recover
spontaneous breaking of chiral symmetry for the nearest-neighbor and nnn
theories. For non-zero baryon density we study the nearest-neighbor theory
only, and show that the pattern of spontaneous symmetry breaking depends on the
baryon density.Comment: 31 pages, 5 EPS figures. Corrected Eq. (6.1
Out-of-equilibrium evolution of scalar fields in FRW cosmology: renormalization and numerical simulations
We present a renormalized computational framework for the evolution of a
self-interacting scalar field (inflaton) and its quantum fluctuations in an FRW
background geometry. We include a coupling of the field to the Ricci scalar
with a general coupling parameter . We take into account the classical and
quantum back reactions, i.e., we consider the the dynamical evolution of the
cosmic scale factor. We perform, in the one-loop and in the large-N
approximation, the renormalization of the equation of motion for the inflaton
field, and of its energy momentum tensor. Our formalism is based on a
perturbative expansion for the mode functions, and uses dimensional
regularization. The renormalization procedure is manifestly covariant and the
counter terms are independent of the initial state. Some shortcomings in the
renormalization of the energy-momentum tensor in an earlier publication are
corrected. We avoid the occurence of initial singularities by constructing a
suitable class of initial states. The formalism is implemented numerically and
we present some results for the evolution in the post-inflationary preheating
era.Comment: 44 pages, uses latexsym, 6 pages with 11 figures in a .ps fil
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How are management fashions institutionalized? The role of institutional work
We explore how transitory management fashions become institutionalized. Based on the concepts of institutional entrepreneurship and institutional work, we postulate that fashionable management practices acquire permanence when they are anchored within fieldwide institutions. The building of such institutions requires various types of institutional work, including political work, technical work and cultural work. Based on a review of the empirical literature on various management fashions, we identify the actors engaging in these different types of works, and their skills. Our results suggest that the institutionalization effect is stronger if more types of institutional work are deployed and if the skill sets of the involved actors vary. We also argue that institutional construction in the case of management fashions is likely to take the form of decentralized `partaking' rather than being led by a single dominant institutional entrepreneur. We conclude with implications for the study of management fashions and the role of agency in institutionalization
The SAMPLE Experiment and Weak Nucleon Structure
One of the key elements to understanding the structure of the nucleon is the
role of its quark-antiquark sea in its ground state properties such as charge,
mass, magnetism and spin. In the last decade, parity-violating electron
scattering has emerged as an important tool in this area, because of its
ability to isolate the contribution of strange quark-antiquark pairs to the
nucleon's charge and magnetism. The SAMPLE experiment at the MIT-Bates
Laboratory, which has been focused on s-sbar contributions to the proton's
magnetic moment, was the first of such experiments and its program has recently
been completed. In this paper we give an overview of some of the experimental
aspects of parity-violating electron scattering, briefly review the theoretical
predictions for strange quark form factors, summarize the SAMPLE measurements,
and place them in context with the program of experiments being carried out at
other electron scattering facilities such as Jefferson Laboratory and the Mainz
Microtron.Comment: 61 pages, review articl
Can topological defects be formed during preheating ?
We study the dynamics of a scalar field \Phi with the potential
g(|\Phi|^2-\eta^2)^2/2 (g=self-coupling constant, \eta=symmetry breaking scale)
after inflation and make clear whether topological defects can ever be formed
during preheating. In particular, we pay attention to GUT defects (\eta \sim
10^{15}GeV - 10^{17}GeV), and consider three types of fluctuations. The first
one is produced due to parametric resonance, the second is due to the negative
curvature of the potential, and the last is created during inflation. We search
for the parameter region that nonthermal fluctuations of the scalar field
produced through the parametric resonant decay of its homogeneous part do not
lead to defect formation. We find that this region is rather wide, and the GUT
defects are not produced after inflation. This fact shows that the positiveness
of the effective mass square of the field and production of large fluctuations
whose amplitude is as large as that of homogeneous mode are not enough
conditions for full symmetry restoration.Comment: 10 pages, RevTex, 17 postscript figures included. The version to be
published in Physical Review
Discrete symmetries, invisible axion and lepton number symmetry in an economic 3-3-1 model
We show that Peccei-Quinn and lepton number symmetries can be a natural
outcome in a 3-3-1 model with right-handed neutrinos after imposing a Z_11 x
Z_2 symmetry. This symmetry is suitably accommodated in this model when we
augmented its spectrum by including merely one singlet scalar field. We work
out the breaking of the Peccei-Quinn symmetry, yielding the axion, and study
the phenomenological consequences. The main result of this work is that the
solution to the strong CP problem can be implemented in a natural way, implying
an invisible axion phenomenologically unconstrained, free of domain wall
formation and constituting a good candidate for the cold dark matter.Comment: 17 pages, Revtex
Appraising empirical applications of Structuration Theory in management and organization studies
There is an increasing interest in the application of Structuration Theory in the fields of management and organization studies. Based upon a thorough literature review, we have come up with a data-set to assess how Structuration Theory has been used in empirical research. We use three key concepts of this theory (duality of structure, knowledgeability, and time-space) as sensitizing concepts for our analysis. We conclude that the greatest potential of Structuration Theory for management and organization studies is to view it as a process theory that offers a distinct building block for explaining intra and interorganizational change, as exemplified through concepts such as routine, script, genre, practice, and discourse
Magnetic Field Generation in Stars
Enormous progress has been made on observing stellar magnetism in stars from
the main sequence through to compact objects. Recent data have thrown into
sharper relief the vexed question of the origin of stellar magnetic fields,
which remains one of the main unanswered questions in astrophysics. In this
chapter we review recent work in this area of research. In particular, we look
at the fossil field hypothesis which links magnetism in compact stars to
magnetism in main sequence and pre-main sequence stars and we consider why its
feasibility has now been questioned particularly in the context of highly
magnetic white dwarfs. We also review the fossil versus dynamo debate in the
context of neutron stars and the roles played by key physical processes such as
buoyancy, helicity, and superfluid turbulence,in the generation and stability
of neutron star fields.
Independent information on the internal magnetic field of neutron stars will
come from future gravitational wave detections. Thus we maybe at the dawn of a
new era of exciting discoveries in compact star magnetism driven by the opening
of a new, non-electromagnetic observational window.
We also review recent advances in the theory and computation of
magnetohydrodynamic turbulence as it applies to stellar magnetism and dynamo
theory. These advances offer insight into the action of stellar dynamos as well
as processes whichcontrol the diffusive magnetic flux transport in stars.Comment: 41 pages, 7 figures. Invited review chapter on on magnetic field
generation in stars to appear in Space Science Reviews, Springe
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
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