543 research outputs found
Constraints on discrete symmetries from anomaly cancellation in compactified superstring theories
Compactified string theories give rise to discrete symmetries which are
essential if they are to provide a realistic low energy theory. We find that in
a class of four dimensional string theories these symmetries are constrained by
similar conditions to those discrete anomaly cancellation conditions found in
the case the discrete symmetry is a residue of a spontaneously broken gauge
symmetry. Such conditions strongly constrain the allowed form of the low energy
effective theory.Comment: 8 pages, OUTP-93-14
QCD-supression by Black Hole Production at the LHC
Possible consequences of the production of small black holes at the LHC for
different scenarios with large extra dimensions are investigated. The effects
from black hole production on some standard jet observables are examined,
concentrating on the reduction of the QCD cross section. It is found that black
hole production of partons interacting on a short enough distance indeed seem
to generate a drastic drop in the QCD cross section. However from an
experimental point of view this will in most cases be camouflaged by energetic
radiation from the black holes
Large N limit of Extremal Non-supersymmetric Black Holes
The large N limit of extremal non-supersymmetric Type-I five-dimensional
string black holes is studied from the point of view of D-branes.
We find that the agreement between the D-brane and the black-hole picture is
due to an asymptotic restoration of supersymmetry in the large limit in
which both pictures are compared.
In that limit Type-I string perturbation theory is effectively embedded into
a Type-IIB perturbation theory with unbroken supersymmetric charges whose
presence guarantees the non-renormalization of mass and entropy as the
effective couplings are increased. In this vein, we also study the near-horizon
geometry of the Type-I black hole using D5-brane probes to find that the low
energy effective action for the probe is identical to the corresponding one in
the auxiliary Type-IIB theory in the large N limit.Comment: 25 pages, harvmac, typos corrected and references adde
Unparticle Physics in the Moller Scattering
We investigate the virtual effects of vector unparticles in the Moller
scattering. We derive the analytic expression for scattering amplitudes with
unpolarized beams. We obtain 95% confidence level limits on the unparticle
couplings and with integrated luminosity of
and and 500 GeV energies. We show
that limits on are more sensitive than .Comment: 10 pages, 5 figures, 4 table
Mass Deformation of the Multiple M2 Branes Theory
Based on recent developments, in this letter we study the one parameter
deformation of 2+1 dimensional gauge theories with scale invariance and N = 8
supersymmetry, which is expected to be the field theory living on a stack of M2
branes. The deformed gauge theory is defined by a Lagrangian and is based on an
infinite set of novel 3-algebras constructed by relaxing the assumption that
the invariant metric is positive definite. Under the Higgs mechanism, we can
obtain the D-branes world volume theory in the presence of background fluxes.Comment: 13pages, no figures, reference adde
Matrix Compactification On Orientifolds
Generalizing previous results for orbifolds, in this paper we describe the
compactification of Matrix model on an orientifold which is a quotient space as
a Yang-Mills theory living on a quantum space. The information of the
compactification is encoded in the action of the discrete symmetry group G on
Euclidean space and a projective representation U of G. The choice of Hilbert
space on which the algebra of U is realized as an operator algebra corresponds
to the choice of a physical background for the compactification. All these data
are summarized in the spectral triple of the quantum space.Comment: 28 pages, late
Brane World Susy Breaking from String/M Theory
String and M-theory realizations of brane world supersymmetry breaking
scenarios are considered in which visible sector Standard Model fields are
confined on a brane, with hidden sector supersymmetry breaking isolated on a
distant brane. In calculable examples with an internal manifold of any volume
the Kahler potential generically contains brane--brane non-derivative contact
interactions coupling the visible and hidden sectors and is not of the no-scale
sequestered form. This leads to non-universal scalar masses and without
additional assumptions about flavor symmetries may in general induce dangerous
sflavor violation even though the Standard Model and supersymmetry branes are
physically separated. Deviations from the sequestered form are dictated by bulk
supersymmetry and can in most cases be understood as arising from exchange of
bulk supergravity fields between branes or warping of the internal geometry.
Unacceptable visible sector tree-level tachyons arise in many models but may be
avoided in certain classes of compactifications. Anomaly mediated and gaugino
mediated contributions to scalar masses are sub-dominant except in special
circumstances such as a flat or AdS pure five--dimensional bulk geometry
without bulk vector multiplets.Comment: Latex, 83 pages, references adde
Modular Cosmology, Thermal Inflation, Baryogenesis and Predictions for Particle Accelerators
Modular cosmology is plagued by overproduction of unwanted relics, gravitinos
and especially moduli, at relatively low energy scales. Thermal inflation
provides a compelling solution to this moduli problem, but invalidates most
baryogenesis scenarios. We propose a simple model in which the MSSM plus
neutrino mass term is supplemented by a minimal flaton sector to
drive the thermal inflation, and make two crucial assumptions: the flaton
vacuum expectation value generates the -term of the MSSM and . The second assumption is particularly interesting in that it
violates a well known constraint, implying that there exists a nearby deep
non-MSSM vacuum, and provides a clear signature of our model which can be
tested at future particle accelerators. We show that our model leads to thermal
inflation followed by Affleck-Dine leptogenensis along the flat
direction. A key feature of our leptogenesis scenario is that the flat
direction is also induced to temporarily acquire a large value, playing a
crucial role in the leptogenesis, as well as dynamically shielding the field
configuration from the deep non-MSSM minimum, ensuring that the fields relax
into our MSSM vacuum.Comment: v3; 19 pages, 3 figures; added a reference for section
A Simple n-Dimensional Intrinsically Universal Quantum Cellular Automaton
We describe a simple n-dimensional quantum cellular automaton (QCA) capable
of simulating all others, in that the initial configuration and the forward
evolution of any n-dimensional QCA can be encoded within the initial
configuration of the intrinsically universal QCA. Several steps of the
intrinsically universal QCA then correspond to one step of the simulated QCA.
The simulation preserves the topology in the sense that each cell of the
simulated QCA is encoded as a group of adjacent cells in the universal QCA.Comment: 13 pages, 7 figures. In Proceedings of the 4th International
Conference on Language and Automata Theory and Applications (LATA 2010),
Lecture Notes in Computer Science (LNCS). Journal version: arXiv:0907.382
Supersymmetric Unification Without Low Energy Supersymmetry And Signatures for Fine-Tuning at the LHC
The cosmological constant problem is a failure of naturalness and suggests
that a fine-tuning mechanism is at work, which may also address the hierarchy
problem. An example -- supported by Weinberg's successful prediction of the
cosmological constant -- is the potentially vast landscape of vacua in string
theory, where the existence of galaxies and atoms is promoted to a vacuum
selection criterion. Then, low energy SUSY becomes unnecessary, and
supersymmetry -- if present in the fundamental theory -- can be broken near the
unification scale. All the scalars of the supersymmetric standard model become
ultraheavy, except for a single finely tuned Higgs. Yet, the fermions of the
supersymmetric standard model can remain light, protected by chiral symmetry,
and account for the successful unification of gauge couplings. This framework
removes all the difficulties of the SSM: the absence of a light Higgs and
sparticles, dimension five proton decay, SUSY flavor and CP problems, and the
cosmological gravitino and moduli problems. High-scale SUSY breaking raises the
mass of the light Higgs to about 120-150 GeV. The gluino is strikingly long
lived, and a measurement of its lifetime can determine the ultraheavy scalar
mass scale. Measuring the four Yukawa couplings of the Higgs to the gauginos
and higgsinos precisely tests for high-scale SUSY. These ideas, if confirmed,
will demonstrate that supersymmetry is present but irrelevant for the hierarchy
problem -- just as it has been irrelevant for the cosmological constant problem
-- strongly suggesting the existence of a fine-tuning mechanism in nature.Comment: Typos and equations fixed, references adde
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