2,160 research outputs found
Direct collider signatures of large extra dimensions
The realization of low (TeV) scale strings usually requires the existence of
large (TeV) extra dimensions where gauge bosons live. The direct production of
Kaluza-Klein excitations of the photon and Z-boson at present and future
colliders is studied in this work. At the LEPII, NLC and Tevatron colliders,
these Kaluza-Klein modes lead to deviations from the standard model
cross-sections, which provide lower bounds on their mass. At the LHC the
corresponding resonances can be produced and decay on-shell, triggering a
characteristic pattern in the distribution of the dilepton invariant mass.Comment: 14 pages, LateX, 5 figure
Limits on the size of extra dimensions
We give a brief summary of present bounds on the size of possible
extra-dimensions from collider experiments.Comment: 13 pages, late
Limits on extra dimensions in orbifold compactifications of superstrings
Perturbative breaking of supersymmetry in four-dimensional string theories
predict in general the existence of new large dimensions at the TeV scale. Such
dimensions can be consistent with perturbative unification up to the Planck
scale in a class of string models and open the exciting possibility of lowering
a part of the massive string spectrum at energies accessible to future
accelerators. The main signature is the production of Kaluza-Klein excitations
which have a very particular structure, strongly correlated with the
supersymmetry breaking mechanism. We present a model independent analysis of
the physics of these states in the context of orbifold compactifications of the
heterotic superstring. In particular, we compute the limits on the size of
large dimensions used to break supersymmetry.Comment: 16 pages, CPTH-A257.079
Large Dimensions and String Physics in Future Colliders
We review the status of low-scale string theories and large extra-dimensions.
After an overview on different string realizations, we discuss some of the main
important problems and we summarize present bounds on the size of possible
extra-dimensions from collider experiments.Comment: 58 pages, latex, 8 eps figure
Brane to bulk supersymmetry breaking and radion force at micron distances
We study mediation of supersymmetry breaking in the bulk, in models with
primordial supersymmetry breaking on D-branes at the string scale, in the TeV
region. We compute the gravitino and scalar masses up to one-loop level, as
well as the radion coupling to matter. We find that the latter mediates a model
independent force at submillimeter distances that can be tested in
micro-gravity experiments for any dimensionality of the bulk. In the case of
two large dimensions, our type I string framework provides an example which
allows to stabilize the radion potential and determine the desired hierarchy
between the string and Planck scales.Comment: One equation and one figure corrected. Two references added. Version
to be published in Nuclear Physics
F-GUTs with Mordell-Weil U(1)'s
In this note we study the constraints on F-theory GUTs with extra 's in
the context of elliptic fibrations with rational sections. We consider the
simplest case of one abelian factor (Mordell-Weil rank one) and investigate the
conditions that are induced on the coefficients of its Tate form. Converting
the equation representing the generic hypersurface to this Tate's
form we find that the presence of a U(1), already in this local description, is
consistent with the exceptional and non-abelian
singularities. We briefly comment on a viable effective
F-theory model.Comment: 13 page
Neutrino mass textures from F-theory
Experimental data on the neutrino mixing and masses strongly suggest an
underlying approximate symmetry of the relevant Yukawa superpotential terms.
Intensive phenomenological explorations during the last decade indicate that
permutation symmetries such as S_4, A_4 and their subgroups, under certain
assumptions and vacuum alignments, predict neutrino mass textures compatible
with such data. Motivated by these findings, in the present work we analyse the
neutrino properties in F-theory GUT models derived in the framework of the
maximal underlying E_8 symmetry in the elliptic fibration. More specifically,
we consider local F-SU(5) GUT models and study in detail spectral cover
geometries with monodromies associated to the finite symmetries S_4, A_4 and
their transitive subgroups, including the dihedral group D_4 and Z_2 X Z_2. We
discuss various issues that emerge in the implementation of S_4, A_4 neutrino
models in the F-theory context and suggest how these can be resolved. Realistic
models are presented for the case of monodromies based on their transitive
subgroups. We exemplify this procedure with a detailed analysis performed for
the case of Z_2 X Z_2 model.Comment: 37 pages, 3 figures, revised versio
Production of Kaluza-Klein States at Future Colliders
Perturbative breaking of supersymmetry in four-dimensional string theories
predict in general the existence of new large dimensions at the TeV scale. Such
large dimensions lie in a domain of energies accessible to particle
accelerators. Their main signature is the production of Kaluza-Klein
excitations which can be detected at future colliders. We study this
possibility for hadron colliders (TEVATRON, LHC) and colliders
(LEP-200, NLC-500).Comment: 13 pages, LATEX, 4 postscript figures appended at the end,
CPTH-A293.0294 and IEM-FT-84/9
On the existence of singularity-free solutions in quartic gravity
We study a general field theory of a scalar field coupled to gravitation
through a quadratic Gauss-Bonnet term . We show that,
under mild assumptions about the function , the classical solutions
in a spatially flat FRW background include singularity - free solutions.Comment: 9 pages, LATEX, uses epsf.tex macro, (1 figure included in
uuencode+compress EPSF form), IOA-29
Kaluza-Klein States versus Winding States: Can Both Be Above the String Scale?
When closed strings propagate in extra compactified dimensions, a rich
spectrum of Kaluza-Klein states and winding states emerges. Since the masses of
Kaluza-Klein states and winding states play a reciprocal role, it is often
believed that either the lightest Kaluza-Klein states or the lightest winding
states must be at or below the string scale. In this paper, we demonstrate that
this conclusion is no longer true for compactifications with non-trivial shape
moduli. Specifically, we demonstrate that toroidal compactifications exist for
which all Kaluza-Klein states as well as all winding states are heavier than
the string scale. This observation could have important phenomenological
implications for theories with reduced string scales, suggesting that it is
possible to cross the string scale without detecting any states associated with
spacetime compactification.Comment: 8 pages, LaTeX, no figure
- …