69 research outputs found
Shape versus Volume: Making Large Flat Extra Dimensions Invisible
Much recent attention has focused on theories with large extra compactified
dimensions. However, while the phenomenological implications of the volume
moduli associated with such compactifications are well understood, relatively
little attention has been devoted to the shape moduli. In this paper, we show
that the shape moduli have a dramatic effect on the corresponding Kaluza-Klein
spectra: they change the mass gap, induce level crossings, and can even be used
to interpolate between theories with different numbers of compactified
dimensions. Furthermore, we show that in certain cases it is possible to
maintain the ratio between the higher-dimensional and four-dimensional Planck
scales while simultaneously increasing the Kaluza-Klein graviton mass gap by an
arbitrarily large factor. This mechanism can therefore be used to alleviate (or
perhaps even eliminate) many of the experimental bounds on theories with large
extra spacetime dimensions.Comment: 9 pages, LaTeX, 5 figure
Electroweak constraints on warped models with custodial symmetry
It has been recently argued that realistic models with warped extra
dimensions can have Kaluza-Klein particles accessible at the Large Hadron
Collider if a custodial symmetry, SU(2)_V \times P_{LR}, is used to protect the
T parameter and the coupling of the left-handed bottom quark to the Z gauge
boson. In this article we emphasize that such a symmetry implies that the loop
corrections to both the T parameter and the Z b_L \bar{b}_L coupling are
calculable. In general, these corrections are correlated, can be sizable, and
should be considered to determine the allowed parameter space region in models
with warped extra dimensions and custodial symmetry, including Randall-Sundrum
models with a fundamental Higgs, models of gauge-Higgs unification and
Higgsless models. As an example, we derive the constraints that arise on a
representative model of gauge-Higgs unification from a global fit to the
precision electroweak observables. A scan over the parameter space typically
leads to a lower bound on the Kaluza-Klein excitations of the gauge bosons of
about 2-3 TeV, depending on the configuration. In the fermionic sector one can
have Kaluza-Klein excitations with masses of a few hundred GeV. We present the
constraints on these light fermions from recent Tevatron searches, and explore
interesting discovery channels at the LHC.Comment: 38 pages, 8 figure
Taxonomic review of the coral Porites colonensis (Scleractinia: Poritidae) in the Colombian Caribbean
Porites colonensis is a coral from the Caribbean Sea; colonies are foliaceous, undulated, and plate-like. Polyps are dark brown or red with small bright white or green centers; Pali are present in corallites and the septal plan is bisymmetrical, conformed by three fused ventral septa, a dorsal solitary septum, and two pairs of lateral septa at each side of the dorso-ventral axis. P. colonensis is similar and can be confused with the smooth varieties of Porites astreoides and Porites branneri. There are three specimens collected from Colombia and previously identified as P. colonensis: one from Golfo de Urabá (Darién ecoregion), other from Islas del Rosario (Coralline Archipelagos ecoregion), and another from an unspecified locality, in addition to one published observation from the Golfo de Urabá without collected specimens. A recent finding of other specimens in the Tayrona National Natural Park (TNNP, Tayrona ecoregion) and the absence of a rigorous taxonomic revision for all specimens collected from Colombia showed that it was necessary to review the presence and distribution of P. colonensis in the Colombian Caribbean. A taxonomic review was done for all specimens collected from Colombia and previously identified as P. colonensis. Then, the morphologic variability of specimens that were confirmed as P. colonensis was described. Only the specimens from TNNP agreed with the holotype description of P. colonensis, while others agreed with flat varieties of P. astreoides. Thus, the presence of P. colonensis is confirmed for the first time for Colombia, but its presence in other Colombian localities outside Tayrona ecoregion could not be demonstrated. This is the only confirmed record of this species for the South American continental shelf. Furthermore, the skeletal characteristics of Colombian P. colonensis corallites showed large variability, exceeding the ranges previously described for the species
Proton Stability in Six Dimensions
We show that Lorentz and gauge invariance explain the long proton lifetime
within the standard model in six dimensions. The baryon-number violating
operators have mass dimension 15 or higher. Upon TeV-scale compactification of
the two universal extra dimensions on a square orbifold, a discrete
subgroup of the 6-dimensional Lorentz group continues to forbid dangerous
operators.Comment: PRL accepted versio
Opaque Branes in Warped Backgrounds
We examine localized kinetic terms for gauge fields which can propagate into
compact, warped extra dimensions. We show that these terms can have a relevant
impact on the values of the Kaluza-Klein (KK) gauge field masses, wave
functions, and couplings to brane and bulk matter. The resulting
phenomenological implications are discussed. In particular, we show that the
presence of opaque branes, with non-vanishing brane-localized gauge kinetic
terms, allow much lower values of the lightest KK mode than in the case of
transparent branes. Moreover, we show that if the large discrepancies among the
different determinations of the weak mixing angle would be solved in favor of
the value obtained from the lepton asymmetries, bulk electroweak gauge fields
in warped-extra dimensions may lead to an improvement of the agreement of the
fit to the electroweak precision data for a Higgs mass of the order of the weak
scale and a mass of the first gauge boson KK excitation most likely within
reach of the LHC.Comment: 37 pages, 12 figures, improved analysis of the precision electroweak
constraint
Warped Radion Dark Matter
Warped scenarios offer an appealing solution to the hierarchy problem. We
consider a non-trivial deformation of the basic Randall-Sundrum framework that
has a KK-parity symmetry. This leads to a stable particle beyond the Standard
Model, that is generically expected to be the first KK-parity odd excitation of
the radion field. We consider the viability of the KK-radion as a DM candidate
in the context of thermal and non-thermal production in the early universe. In
the thermal case, the KK-radion can account for the observed DM density when
the radion decay constant is in the natural multi-TeV range. We also explore
the effects of coannihilations with the first KK excitation of the RH top, as
well as the effects of radion-Higgs mixing, which imply mixing between the
KK-radion and a KK-Higgs (both being KK-parity odd). The non-thermal scenario,
with a high radion decay constant, can also lead to a viable scenario provided
the reheat temperature and the radion decay constant take appropriate values,
although the reheat temperature should not be much higher than the TeV scale.
Direct detection is found to be feasible if the DM has a small (KK-parity odd)
Higgs admixture. Indirect detection via a photon signal from the galactic
center is an interesting possibility, while the positron and neutrino fluxes
from KK-radion annihilations are expected to be rather small. Colliders can
probe characteristic aspects of the DM sector of warped scenarios with
KK-parity, such as the degeneracy between the radion and the KK-radion (DM)
modes.Comment: 43 pages, 16 figures; added reference
Dirac gauginos, R symmetry and the 125 GeV Higgs
We study a supersymmetric scenario with a quasi exact R-symmetry in light of the discovery of a Higgs resonance with a mass of 125 GeV. In such a framework, the additional adjoint superfields, needed to give Dirac masses to the gauginos, contribute both to the Higgs mass and to electroweak precision observables. We analyze the interplay between the two aspects, finding regions in parameter space in which the contributions to the precision observables are under control and a 125 GeV Higgs boson can be accommodated. We estimate the fine-tuning of the model finding regions of the parameter space still unexplored by the LHC with a fine-tuning considerably improved with respect to the minimal supersymmetric scenario. In particular, sizable non-holomorphic (non-supersoft) adjoints masses are required to reduce the fine-tuning
The GUT Scale and Superpartner Masses from Anomaly Mediated Supersymmetry Breaking
We consider models of anomaly-mediated supersymmetry breaking (AMSB) in which
the grand unification (GUT) scale is determined by the vacuum expectation value
of a chiral superfield. If the anomaly-mediated contributions to the potential
are balanced by gravitational-strength interactions, we find a
model-independent prediction for the GUT scale of order . The GUT threshold also affects superpartner masses, and can easily
give rise to realistic predictions if the GUT gauge group is asymptotically
free. We give an explicit example of a model with these features, in which the
doublet-triplet splitting problem is solved. The resulting superpartner
spectrum is very different from that of previously considered AMSB models, with
gaugino masses typically unifying at the GUT scale.Comment: 17 page
"L = R" - U(1) R as the origin of leptonic 'RPV'
A classification of phenomenologically interesting supersymmetric extensions of the Standard-Model with a U(1) R symmetry is presented. Some of these are consistent with subsets of leptonic or baryonic "R-parity violating" (RPV) operators, thereby providing a natural motivation for them. We then focus on a particular class of models in which the U(1) R symmetry coincides with lepton number when restricted to the SM sector. In this case, the extension of lepton number to the superpartners is "non-standard", implying, in particular, the existence of the leptonic RPV operators LLE c and LQD c, and a vacuum structure where one of the left-handed sneutrinos acquires a significant vacuum-expectation-value, while not being constrained by neutrino mass bounds. The model can be naturally consistent with bounds from electroweak precision measurements and flavor-changing processes. It can also easily accommodate the recently measured Higgs mass due to the existence of a scalar triplet that couples to the Higgs with an order one coupling, with only moderate fine-tuning. The phenomenology is rather rich and distinctive, with features such as heavy-but-natural Dirac gauginos, relaxed bounds on squarks, resonant slepton/sneutrino production, lepto-quark signals, as well as an interesting connection to neutrino physics arising from R-breaking. The broad qualitative features are discussed in this paper, with a more detailed phenomenological study carried out in a companion paper [1]
Effective Lagrangians and Light Gravitino Phenomenology
We construct the low-energy effective lagrangian for a light gravitino
coupled to the minimal supersymmetric standard model under the assumption that
supersymmetry breaking is communicated to the observable sector dominantly
through soft terms. Our effective lagrangian is written in terms of the
spin-1/2 Goldstino (the longitudinal component of the gravitino) transforming
under a non-linear realization of supersymmetry. In this lagrangian, the
Goldstino is derivatively coupled and all couplings of the Goldstino to light
fields are determined uniquely by the supersymmetry-breaking scale \sqrt{F}.
This lagrangian is therefore a useful starting point for further investigation
of the light gravitino in gauge-mediated supersymmetry breaking models. We show
that the invisible width of the Z into Goldstinos gives the constraint \sqrt{F}
> 140 GeV.Comment: 15 pages, LaTeX2e, 1 eps figure. Removed erroneous claim of coupling
of photon to gravitino to photons at order M^2 E^2 / F^2. Strongest bound is
from invisible Z width, giving F > (140 GeV)^
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