213 research outputs found
Consistent Linearized Gravity in Brane Backgrounds
A globally consistent treatment of linearized gravity in the Randall-Sundrum
background with matter on the brane is formulated. Using a novel gauge, in
which the transverse components of the metric are non-vanishing, the brane is
kept straight. We analyze the gauge symmetries and identify the physical
degrees of freedom of gravity. Our results underline the necessity for
non-gravitational confinement of matter to the brane.Comment: 15 page
Brane-skyrmions and wrapped states
In the context of a brane world and including an induced curvature term in
the brane action, we obtain the effective lagrangian for the Goldstone bosons
(branons) associated with the spontaneous breaking of the translational
invariance in the bulk. In addition to the branons, this effective action has
Skyrmion-like solitonic states which can be understood as holes in the brane.
We study their main properties such as mass and size, the Skyrmion-branon
interaction and their possible fermionic quantization. We also consider states
where the brane is wrapped around the extra dimensions and their relation with
the brane-skyrmions. Finally, we extend our results to higher-dimensional
branes, such as those appearing in M-theory, where brane-skyrmions could also
be present.Comment: 35 pages, 7 figures. Revised version. Appendix and new references
included. To appear in Phys. Rev.
Central exclusive production of longlived gluinos at the LHC
We examine the possibility of producing gluino pairs at the LHC via the
exclusive reaction pp -> p+gluino+gluino+p in the case where the gluinos are
long lived. Such long lived gluinos are possible if the scalar super-partners
have large enough masses. We show that it may be possible to observe the
gluinos via their conversion to R-hadron jets and measure their mass to better
than 1% accuracy for masses below 350 GeV with 300/fb of data.Comment: 13 pages, 9 figures. Minor corrections to version
Dynamics of Brane-World Cosmological Models
We show that generically the initial singularity is isotropic in spatially
homogeneous cosmological models in the brane-world scenario. We then argue that
it is plausible that the initial singularity is isotropic in typical brane
world cosmological models. Therefore, brane cosmology naturally gives rise to a
set of initial data that provide the conditions for inflation to subsequently
take place, thereby solving the initial conditions problem and leading to a
self--consistent and viable cosmology.Comment: Final version. To appear in Physical Revie
Baryon number violation, baryogenesis and defects with extra dimensions
In generic models for grand unified theories(GUT), various types of baryon
number violating processes are expected when quarks and leptons propagate in
the background of GUT strings. On the other hand, in models with large extra
dimensions, the baryon number violation in the background of a string is not
trivial because it must depend on the mechanism of the proton stabilization. In
this paper we argue that cosmic strings in models with extra dimensions can
enhance the baryon number violation to a phenomenologically interesting level,
if the proton decay is suppressed by the mechanism of localized wavefunctions.
We also make some comments on baryogenesis mediated by cosmological defects. We
show at least two scenarios will be successful in this direction. One is the
scenario of leptogenesis where the required lepton number conversion is
mediated by cosmic strings, and the other is the baryogenesis from the decaying
cosmological domain wall. Both scenarios are new and have not been discussed in
the past.Comment: 20pages, latex2e, comments and references added, to appear in PR
Cosmic F- and D-strings
Macroscopic fundamental and Dirichlet strings have several potential
instabilities: breakage, tachyon decays, and confinement by axion domain walls.
We investigate the conditions under which metastable strings can exist, and we
find that such strings are present in many models. There are various
possibilities, the most notable being a network of (p,q) strings. Cosmic
strings give a potentially large window into string physics.Comment: 27 pages, 5 figures; v. 5: JHEP style, added comments in section 2.
Towards a Resolution of the Cosmological Singularity in Non-local Higher Derivative Theories of Gravity
One of the greatest problems of standard cosmology is the Big Bang
singularity. Previously it has been shown that non-local ghostfree
higher-derivative modifications of Einstein gravity in the ultra-violet regime
can admit non-singular bouncing solutions. In this paper we study in more
details the dynamical properties of the equations of motion for these theories
of gravity in presence of positive and negative cosmological constants and
radiation. We find stable inflationary attractor solutions in the presence of a
positive cosmological constant which renders inflation {\it geodesically
complete}, while in the presence of a negative cosmological constant a cyclic
universe emerges. We also provide an algorithm for tracking the super-Hubble
perturbations during the bounce and show that the bouncing solutions are free
from any perturbative instability.Comment: 38 pages, 6 figures. V2: Added: a word to the title, clarifications,
an appendix, many references. To appear in JCA
About the possibility of five-dimensional effective theories for low-energy QCD
The AdS/QCD models suggest an interesting idea that the effective theory of
low-energy QCD may be formulated as a 5-dimensional field theory in the weak
coupling regime in which the fifth coordinate plays a role of inverse energy
scale. Taking the point of view that this is just an efficient parametrization
of the non-perturbative dynamics of strong interactions, we discuss on a
qualitative level an alternative possibility for a simpler 5-dimensional
parametrization of main phenomena in the low-energy QCD. We propose to
interpret the effect of chiral symmetry breaking as an effective appearance of
compactified extra dimension with the radius of the order of inverse scale of
chiral symmetry breaking. Following some heuristic arguments two dual scenarios
for the emergence of the excited light mesons are introduced: In the first
scenario, the meson resonances are interpreted as the effects of Kaluza-Klein
excitations of quarks inside mesons, in the second one, as the formation of
gluon strings wound around the compactified dimension an appropriate number of
times. Matching of these scenarios permits to express the slope of radial Regge
trajectories through the order parameters of the chiral symmetry breaking, with
the compactification radius being excluded. This example shows qualitatively
that the extra dimension may play an auxiliary role providing a short way for
deriving new relations.Comment: 11 pages, accepted by Eur. Phys. J.
New limits on nucleon decays into invisible channels with the BOREXINO Counting Test Facility
The results of background measurements with the second version of the
BOREXINO Counting Test Facility (CTF-II), installed in the Gran Sasso
Underground Laboratory, were used to obtain limits on the instability of
nucleons, bounded in nuclei, for decays into invisible channels ():
disappearance, decays to neutrinos, etc. The approach consisted of a search for
decays of unstable nuclides resulting from and decays of parents
C, C and O nuclei in the liquid scintillator and the water
shield of the CTF. Due to the extremely low background and the large mass (4.2
ton) of the CTF detector, the most stringent (or competitive) up-to-date
experimental bounds have been established: y, y, y and y, all at 90% C.L.Comment: 22 pages, 3 figures,submitted to Phys.Lett.
Search for Doubly-Charged Higgs Bosons at LEP
Doubly-charged Higgs bosons are searched for in e^+e^- collision data
collected with the L3 detector at LEP at centre-of-mass energies up to 209 GeV.
Final states with four leptons are analysed to tag the pair-production of
doubly charged Higgs bosons. No significant excess is found and lower limits at
95% confidence level on the doubly-charged Higgs boson mass are derived. They
vary from 95.5 GeV to 100.2 GeV, depending on the decay mode. Doubly-charged
Higgs bosons which couple to electrons would modify the cross section and
forward-backward asymmetry of the e^+e^- -> e^+e^- process. The measurements of
these quantities do not deviate from the Standard Model expectations and
doubly-charged Higgs bosons with masses up to the order of a TeV are excluded
- …