404 research outputs found
Orbifold Reduction Of The Quark-Lepton Symmetric Model
We investigate the quark-lepton symmetric gauge group in five dimensions,
with the gauge symmetry broken by a combination of orbifold compactification of
the extra dimension and the Higgs mechanism. The gauge sector of the model is
investigated and contrasted with the four dimensional case. We obtain lower
bounds on the mass of the exotic gauge bosons, the inverse compactification
scale and the exotic leptons. Light neutrinos are obtained without requiring
any scale larger than a TeV. However an ultra-violet cut-off of order
GeV is required to suppress proton decay inducing non-renormalizable operators.Comment: References added to match PRD versio
The Effective Potential And Additional Large Radius Compactified Space-Time Dimensions
The consequences of large radius extra space-time compactified dimensions on
the four dimensional one loop effective potential are investigated for a model
which includes scalar self interactions and Yukawa coupling to fermions. The
Kaluza-Klein tower of states associated with the extra compact dimensions
shifts the location of the effective potential minimum and modifies its
curvature. The dependence of these effects on the radius of the extra dimension
is illustrated for various choices of coupling constants and masses. For large
radii, the consequence of twisting the fermion boundary condition on the
compactified dimensions is numerically found to produce but a negligible effect
on the effective potential.Comment: 14 pages, LaTeX, 6 Postscript figure
The geometrical form for the string space-time action
In the present article, we derive the space-time action of the bosonic string
in terms of geometrical quantities. First, we study the space-time geometry
felt by probe bosonic string moving in antisymmetric and dilaton background
fields. We show that the presence of the antisymmetric field leads to the
space-time torsion, and the presence of the dilaton field leads to the
space-time nonmetricity. Using these results we obtain the integration measure
for space-time with stringy nonmetricity, requiring its preservation under
parallel transport. We derive the Lagrangian depending on stringy curvature,
torsion and nonmetricity.Comment: 13 page
Dualisation of Dualities, I
We analyse the global (rigid) symmetries that are realised on the bosonic
fields of the various supergravity actions obtained from eleven-dimensional
supergravity by toroidal compactification followed by the dualisation of some
subset of fields. In particular, we show how the global symmetries of the
action can be affected by the choice of this subset. This phenomenon occurs
even with the global symmetries of the equations of motion. A striking
regularity is exhibited by the series of theories obtained respectively without
any dualisation, with the dualisation of only the Ramond-Ramond fields of the
type IIA theory, with full dualisation to lowest degree forms, and finally for
certain inverse dualisations (increasing the degrees of some forms) to give the
type IIB series. These theories may be called the GL_A, D, E and GL_B series
respectively. It turns out that the scalar Lagrangians of the E series are
sigma models on the symmetric spaces K(E_{11-D})\backslash E_{11-D} (where K(G)
is the maximal compact subgroup of G) and the other three series lead to models
on homogeneous spaces K(G) \backslash G\semi \R^s. These can be understood from
the E series in terms of the deletion of positive roots associated with the
dualised scalars, which implies a group contraction. We also propose a
constrained Lagrangian version of the even dimensional theories exhibiting the
full duality symmetry and begin a systematic analysis of abelian duality
subalgebras.Comment: Latex, 82 pages, minor corrections and references adde
Testing the equivalence principle: why and how?
Part of the theoretical motivation for improving the present level of testing
of the equivalence principle is reviewed. The general rationale for optimizing
the choice of pairs of materials to be tested is presented. One introduces a
simplified rationale based on a trichotomy of competing classes of theoretical
models.Comment: 11 pages, Latex, uses ioplppt.sty, submitted to Class. Quantum Gra
Initial Condition for QGP Evolution from NEXUS
We recently proposed a new approach to high energy nuclear scattering, which
treats the initial stage of heavy ion collisions in a sophisticated way.
We are able to calculate macroscopic quantities like energy density and
velocity flow at the end of this initial stage, after the two nuclei having
penetrated each other.
In other words, we provide the initial conditions for a macroscopic treatment
of the second stage of the collision.
We address in particular the question of how to incorporate the soft
component properly. We find almost perfect "Bjorken scaling": the rapidity
coincides with the space-time rapidity, whereas the transverse flow is
practically zero. The distribution of the energy density in the transverse
plane shows typically a very "bumpy" structure.Comment: 17 pages, 24 figure
Naturally split supersymmetry
Nonobservation of superparticles till date, new Higgs mass limits from the
CMS and ATLAS experiments, WMAP constraints on relic density, various other low
energy data, and the naturalness consideration, all considered simultaneously
imply a paradigm shift of supersymmetric model building. In this paper we
perform, for the first time, a detailed numerical study of brane-world induced
supersymmetry breaking for both minimal and next-to-minimal scenarios. We
observe that a naturally hierarchical spectrum emerges through an interplay of
bulk, brane-localized and quasi-localized fields, which can gain more relevance
in the subsequent phases of the LHC run.Comment: 6 pages, 6 eps figures; v2: minor updates, to appear in JHE
Classical and Quantum Analysis of Repulsive Singularities in Four Dimensional Extended Supergravity
Non--minimal repulsive singularities (``repulsons'') in extended supergravity
theories are investigated. The short distance antigravity properties of the
repulsons are tested at the classical and the quantum level by a scalar
test--particle. Using a partial wave expansion it is shown that the particle
gets totally reflected at the origin. A high frequency incoming particle
undergoes a phase shift of . However, the phase shift for a
low--frequency particle depends upon the physical data of the repulson. The
curvature singularity at a finite distance turns out to be transparent
for the scalar test--particle and the coordinate singularity at the origin
serves as a repulsive barrier at which particles bounce off.Comment: 20 pages, 14 figure
Domain Walls in Massive Supergravities
We show how toroidally-compactified eleven-dimensional supergravity can be
consistently truncated to yield a variety of maximally-supersymmetric
``massive'' supergravities in spacetime dimensions . The mass terms
arise as a consequence of making a more general ansatz than that in usual
Kaluza-Klein dimensional reduction, in which one or more axions are given an
additional linear dependence on one of the compactification coordinates. The
lower-dimensional theories are nevertheless consistent truncations of
eleven-dimensional supergravity. Owing to the fact that the generalised
reduction commutes neither with U-duality nor with ordinary dimensional
reduction, many different massive theories can result. The simplest examples
arise when just a single axion has the additional linear coordinate dependence.
We find five inequivalent such theories in D=7, and 71 inequivalent ones in
D=4. The massive theories admit no maximally-symmetric vacuum solution, but
they do admit -brane solutions, i.e. domain walls, which preserve half
the supersymmetry. We present examples of these solutions, and their oxidations
to D=11. Some of the latter are new solutions of D=11 supergravity.Comment: latex, 32 papes, no figures, further comments and references adde
New Sum Rules from Low Energy Compton Scattering on Arbitrary Spin Target
We derive two sum rules by studying the low energy Compton scattering on a
target of arbitrary (nonzero) spin j. In the first sum rule, we consider the
possibility that the intermediate state in the scattering can have spin |j \pm
1| and the same mass as the target. The second sum rule applies if the theory
at hand possesses intermediate narrow resonances with masses different from the
mass of the scatterer. These sum rules are generalizations of the
Gerasimov-Drell-Hearn-Weinberg sum rule. Along with the requirement of tree
level unitarity, they relate different low energy couplings in the theory.
Using these sum rules, we show that in certain cases the gyromagnetic ratio can
differ from the "natural" value g=2, even at tree level, without spoiling
perturbative unitarity. These sum rules can be used as constraints applicable
to all supergravity and higher-spin theories that contain particles charged
under some U(1) gauge field. In particular, applied to four dimensional N=8
supergravity in a spontaneously broken phase, these sum rules suggest that for
the theory to have a good ultraviolet behavior, additional massive states need
to be present, such as those coming from the embedding of the N=8 supergravity
in type II superstring theory. We also discuss the possible implications of the
sum rules for QCD in the large-N_c limit.Comment: 18 pages, v2: discussion on black hole contribution is included,
references added; v3: extended discussion in introduction, version to appear
in JHE
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