5,679 research outputs found
Neutrinos, Axions and Conformal Symmetry
We demonstrate that radiative breaking of conformal symmetry (and
simultaneously electroweak symmetry) in the Standard Model with right-chiral
neutrinos and a minimally enlarged scalar sector induces spontaneous breaking
of lepton number symmetry, which naturally gives rise to an axion-like particle
with some unusual features. The couplings of this `axion' to Standard Model
particles, in particular photons and gluons, are entirely determined (and
computable) via the conformal anomaly, and their smallness turns out to be
directly related to the smallness of the masses of light neutrinos.Comment: 10 pages, 2 figures, expanded version, to be published in EPJ
(B-L) Symmetry vs. Neutrino Seesaw
We compute the effective coupling of the Majoron to W bosons at \cO(\hbar)
by evaluating the matrix element of the (B-L) current between the vacuum and a
state. The (B-L) anomaly vanishes, but the amplitude does not vanish
as a result of a UV finite and non-local contribution which is entirely due to
the mixing between left-chiral and right-chiral neutrinos. The result shows how
anomaly-like couplings may arise in spite of the fact that the (B-L) current
remains exactly conserved to all orders in , lending additional support
to our previous proposal to identify the Majoron with the axion.Comment: 13 pages, 1 figure, with additional explanations and clarification
The status quo of research on South Africa’s water resource management institutions
The South African water resource management institutional landscape has seen some dramatic changes since the new dispensation came into power in 1994. Not only have legislation and policies changed, but there has also been a significant increase in the number of non-state actors in the policy development process. Water resource governance has therefore become more complex and its regulatory component is being implemented by a number of legislative institutions: catchment management agencies, water user associations, irrigation boards, and international water management bodies. Policy development is influenced by a myriad of non-state actors, scientists included. A comprehensive literature review of research on water resource management institutions published between 1997 and 2011 shows that scientists are focusing predominantly on catchment management agencies and aspects regarding their institutionalisation and organisational functionality. There is much less of a focus on other entities, such as advisory committees, international water management bodies, irrigation boards, the water tribunal and water user associations. What the review has also revealed is that research on water resource management institutions has been conducted predominantly by scientists from the natural sciences. There is therefore an evident need for a research focus on water resource management institutions other than catchment management agencies. In addition, there should be a focus on informal aspects of water resource governance and new theoretical developments, also from disciplines other than the natural sciences, in the fields of water resource governance and politics.Keywords: Water resource management institutions, literature review, catchment management agencies,water user associations, legislation, irrigation boards, catchment forums, international water management bodie
B=3 Tetrahedrally Symmetric Solitons in the Chiral Quark Soliton Model
In this paper, B=3 soliton solutions with tetrahedral symmetry are obtained
numerically in the chiral quark soliton model using the rational map ansatz.
The solution exhibits a triply degenerate bound spectrum of the quark orbits in
the background of tetrahedrally symmetric pion field configuration. The
corresponding baryon density is tetrahedral in shape. Our numerical technique
is independent on the baryon number and its application to is
straightforward.Comment: 4 pages, 3 figure
Bose Condensation and the BTZ Black Hole
Although all popular approaches to quantum gravity are able to recover the
Bekenstein-Hawking entropy-area law in the thermodynamic limit, there are
significant differences in their descriptions of the microstates and in the
application of statistics. Therefore they can have significantly different
phenomenological implications. For example, requiring indistinguishability of
the elementary degrees of freedom should lead to changes in the black hole's
radiative porperties away from the thermodynamic limit and at low temperatures.
We demonstrate this for the Ba\~nados-Teitelboim-Zanelli (BTZ) black hole. The
energy eigenstates and statistical entropy in the thermodynamic limit of the
BTZ black hole were obtained earlier by us via symmetry reduced canonical
quantum gravity. In that model the BTZ black hole behaves as a system of
Bosonic mass shells moving in a one dimensional harmonic trap. Bose
condensation does not occur in the thermodynamic limit but this system
possesses a finite critical temperature, , and exhibits a large condensate
fraction below when the number of shells is finite.Comment: 5 pages, 5 figures. Published versio
Domain walls without cosmological constant in higher order gravity
We consider a class of higher order corrections with arbitrary power of
the curvature tensor to the standard gravity action in arbitrary space-time
dimension . The corrections are in the form of Euler densities and are
unique at each and . We present a generating functional and an explicit
form of the corresponding conserved energy-momentum tensors. The case of
conformally flat metrics is discussed in detail. We show that this class of
corrections allows for domain wall solutions since, despite the presence of
higher powers of the curvature tensor, the singularity structure at the wall is
of the same type as in the standard gravity. However, models with higher order
corrections have larger set of domain wall solutions and the existence of these
solutions no longer depends on the presence of cosmological constants. We find
for example that the Randall-Sundrum scenario can be realized without any need
for bulk and/or brane cosmological constant.Comment: latex, 10 pages, introduction extended, references added, typos
correcte
A Model of Graceful Exit in String Cosmology
We construct, for the first time, a model of graceful exit transition from a
dilaton-driven inflationary phase to a decelerated Friedman-Robertson-Walker
era. Exploiting a demonstration that classical corrections can stabilize a high
curvature string phase while the evolution is still in the weakly coupled
regime, we show that if additional terms of the type that may result from
quantum corrections to the string effective action exist, and induce violation
of the null energy condition, then evolution towards a decelerated
Friedman-Robertson-Walker phase is possible. We also observe that stabilizing
the dilaton at a fixed value, either by capture in a potential minimum or by
radiation production, may require that these quantum corrections are turned
off, perhaps by non-perturbative effects or higher order contributions which
overturn the null energy condition violation.Comment: 17 pages including 9 figures, RevTeX. Uses epsfi
O(d,d) invariance at two and three loops
We show that in a two-dimensional sigma-model whose fields only depend on one
target space co-ordinate, the O(d,d) invariance of the conformal invariance
conditions observed at one loop is preserved at two loops (in the general case
with torsion) and at three loops (in the case without torsion).Comment: 21 pages. Plain Tex. Uses Harvmac ("b" option). Revised Version with
references added and minor errors correcte
Plasma Magnetohydrodynamics and Energy Conversion
Contains reports on four research projects.United States Air Force, Aeronautical Systems Division (Contract AF33(616)-7624)United States Air Force, Aeronautical Systems Division, Aeronautical Accessories Laboratory, Wright-Patterson Air Force Base (Contract AF33(616)-7624
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