14,304 research outputs found
What is the Discrete Gauge Symmetry of the MSSM?
We systematically study the extension of the Supersymmetric Standard Model
(SSM) by an anomaly-free discrete gauge symmetry Z_N. We extend the work of
Ibanez and Ross with N=2,3 to arbitrary values of N. As new fundamental
symmetries, we find four Z_6, nine Z_9 and nine Z_18. We then place three
phenomenological demands upon the low-energy effective SSM: (i) the presence of
the mu-term in the superpotential, (ii) baryon-number conservation upto
dimension-five operators, and (iii) the presence of the see-saw neutrino mass
term LHLH. We are then left with only two anomaly-free discrete gauge
symmetries: baryon-triality, B_3, and a new Z_6, which we call proton-hexality,
P_6. Unlike B_3, P_6 prohibits the dimension-four lepton-number violating
operators. This we propose as the discrete gauge symmetry of the Minimal SSM,
instead of R-parity.Comment: Typo in item 2 below Eq.(6.9) corrected (wrong factor of "3"); 27
pages, 5 table
Cosmic Evolution in Generalised Brans-Dicke Theory
We have studied the Generalised Brans-Dicke theory and obtained exact
solutions of a(t),phi(t),and omega(t) for different epochs of the cosmic
evolution .We discuss how inflation,decceleration,cosmic acceleration can
result from this solution.The time variation of G(t) is also examined.Comment: 12 pages, no figure
Static spherically symmetric perfect fluid solutions in theories of gravity
Static spherically symmetric perfect fluid solutions are studied in metric
theories of gravity. We show that pressure and density do not uniquely
determine ie. given a matter distribution and an equation state, one
cannot determine the functional form of . However, we also show that
matching the outside Schwarzschild-de Sitter-metric to the metric inside the
mass distribution leads to additional constraints that severely limit the
allowed fluid configurations.Comment: 5 page
Dressing the electromagnetic nucleon current
A field-theory-based approach to pion photoproduction off the nucleon is used
to derive a microscopically consistent formulation of the fully dressed
electromagnetic nucleon current in an effective Lagrangian formalism. It is
shown how the rigorous implementation of local gauge invariance at all levels
of the reaction dynamics provides equations that lend themselves to practically
manageable truncations of the underlying nonlinearities of the problem. The
requirement of consistency also suggests a novel way of treating the pion
photoproduction problem. Guided by a phenomenological implementation of gauge
invariance for the truncated equations that has proved successful for pion
photoproduction, an expression for the fully dressed nucleon current is given
that satisfies the Ward-Takahashi identity for a fully dressed nucleon
propagator as a matter of course. Possible applications include meson photo-
and electroproduction processes, bremsstrahlung, Compton scattering, and
processes off nucleons.Comment: 10 pages, 9 figure
Spontaneous emission of graviton by a quantum bouncer
Spontaneous emission of graviton rates for the quantum bouncer states are
evaluated
Radiation damage and defect behavior in ion-implanted, lithium counterdoped silicon solar cells
Boron doped silicon n+p solar cells were counterdoped with lithium by ion implanation and the resultant n+p cells irradiated by 1 MeV electrons. The function of fluence and a Deep Level Transient Spectroscopy (DLTS) was studied to correlate defect behavior with cell performance. It was found that the lithium counterdoped cells exhibited significantly increased radiation resistance when compared to boron doped control cells. It is concluded that the annealing behavior is controlled by dissociation and recombination of defects. The DLTS studies show that counterdoping with lithium eliminates at least three deep level defects and results in three new defects. It is speculated that the increased radiation resistance of the counterdoped cells is due primarily to the interaction of lithium with oxygen, single vacancies and divacancies and that the lithium-oxygen interaction is the most effective in contributing to the increased radiation resistance
Dihedral Families of Quarks, Leptons and Higgs Bosons
We consider finite groups of small order for family symmetry. It is found
that the binary dihedral group Q_6, along with the assumption that the Higgs
sector is of type II, predicts mass matrix of a nearest neighbor interaction
type for quarks and leptons. We present a supersymmetric model based on Q_6
with spontaneously induced CP phases. The quark sector contains 8 real
parameters with one independent phase to describe the quark masses and their
mixing. Predictions in the |V_{ub}|-bar{eta}, |V_{ub}|-sin 2 beta(phi_1) and
|V_{ub}|-|V_{td}/V_{ts}| planes are given. The lepton sector contains also 9
parameters. A normal as well as an inverted spectrum of neutrino masses is
possible, and we compute V_{e3}. We find that |V_{e3}|^2 > 10^{-4} in the case
of a normal spectrum, and |V_{e3}|^2 >8 10^{-4} in the case of an inverted
spectrum. It is also found that Q_6 symmetry forbids all Baryon number
violating terms of d=4, and the contributions to EDMs from the A terms vanish
in this model.Comment: 27 pages, 8 figure
Non-rotating and rotating neutron stars in the extended field theoretical model
We study the properties of non-rotating and rotating neutron stars for a new
set of equations of state (EOSs) with different high density behaviour obtained
using the extended field theoretical model. The high density behaviour for
these EOSs are varied by varying the meson self-coupling and
hyperon-meson couplings in such a way that the quality of fit to the bulk
nuclear observables, nuclear matter incompressibility coefficient and
hyperon-nucleon potential depths remain practically unaffected. We find that
the largest value for maximum mass for the non-rotating neutron star is
. The radius for the neutron star with canonical mass is km provided only those EOSs are considered for which maximum mass is
larger than as it is the lower bound on the maximum mass measured
so far. Our results for the very recently discovered fastest rotating neutron
star indicate that this star is supra massive with mass and
circumferential equatorial radius km.Comment: 28 pages, 12 figures. Phys. Rev. C (in press
The cosmological constant and dark energy in braneworlds
We review recent attempts to address the cosmological constant problem and
the late-time acceleration of the Universe based on braneworld models. In
braneworld models, the way in which the vacuum energy gravitates in the 4D
spacetime is radically different from conventional 4D physics. It is possible
that the vacuum energy on a brane does not curve the 4D spacetime and only
affects the geometry of the extra-dimensions, offering a solution to the
cosmological constant problem. We review the idea of supersymmetric large extra
dimensions that could achieve this and also provide a natural candidate for a
quintessence field. We also review the attempts to explain the late-time
accelerated expansion of the universe from the large-distance modification of
gravity based on the braneworld. We use the Dvali-Gabadadze-Porrati model to
demonstrate how one can distinguish this model from dark energy models in 4D
general relativity. Theoretical difficulties in this approach are also
addressed.Comment: Invited Review for a special Gen. Rel. Grav. issue on Dark Energy, 22
pages, 13 figures, references adde
Graviton localization and Newton's law for brane models with a non-minimally coupled bulk scalar field
Brane world models with a non-minimally coupled bulk scalar field have been
studied recently. In this paper we consider metric fluctuations around an
arbitrary gravity-scalar background solution, and we show that the
corresponding spectrum includes a localized zero mode which strongly depends on
the profile of the background scalar field. For a special class of solutions,
with a warp factor of the RS form, we solve the linearized Einstein equations,
for a point-like mass source on the brane, by using the brane bending
formalism. We see that general relativity on the brane is recovered only if we
impose restrictions on the parameter space of the models under consideration.Comment: 17 pages, revised versio
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