929 research outputs found
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
Radiative Electroweak Symmetry Breaking in a Little Higgs Model
We present a new Little Higgs model, motivated by the deconstruction of a
five-dimensional gauge-Higgs model. The approximate global symmetry is
, breaking to , with a gauged subgroup of
, breaking to . Radiative corrections produce an additional small vacuum misalignment,
breaking the electroweak symmetry down to . Novel features of this
model are: the only un-eaten pseudo-Goldstone boson in the effective theory is
the Higgs boson; the model contains a custodial symmetry, which ensures that
at tree-level; and the potential for the Higgs boson is generated
entirely through one-loop radiative corrections. A small negative mass-squared
in the Higgs potential is obtained by a cancellation between the contribution
of two heavy partners of the top quark, which is readily achieved over much of
the parameter space. We can then obtain both a vacuum expectation value of
GeV and a light Higgs boson mass, which is strongly correlated with the
masses of the two heavy top quark partners. For a scale of the global symmetry
breaking of TeV and using a single cutoff for the fermion loops, the
Higgs boson mass satisfies 120 GeV GeV over much of
the range of parameter space. For raised to 10 TeV, these values increase
by about 40 GeV. Effects at the ultraviolet cutoff scale may also raise the
predicted values of the Higgs boson mass, but the model still favors
GeV.Comment: 32 pages, 10 figures, JHEP style. Version accepted for publication in
JHEP. Includes additional discussion of sensitivity to UV effects and
fine-tuning, revised Fig. 9, added appendix and additional references
Induction of microRNAs, mir-155, mir-222, mir-424 and mir-503, promotes monocytic differentiation through combinatorial regulation
Acute myeloid leukemia (AML) involves a block in terminal differentiation of
the myeloid lineage and uncontrolled proliferation of a progenitor state. Using
phorbol myristate acetate (PMA), it is possible to overcome this block in THP-1
cells (an M5-AML containing the MLL-MLLT3 fusion), resulting in differentiation
to an adherent monocytic phenotype. As part of FANTOM4, we used microarrays to
identify 23 microRNAs that are regulated by PMA. We identify four PMA-induced
micro- RNAs (mir-155, mir-222, mir-424 and mir-503) that when overexpressed
cause cell-cycle arrest and partial differentiation and when used in
combination induce additional changes not seen by any individual microRNA. We
further characterize these prodifferentiative microRNAs and show that mir-155
and mir-222 induce G2 arrest and apoptosis, respectively. We find mir-424 and
mir-503 are derived from a polycistronic precursor mir-424-503 that is under
repression by the MLL-MLLT3 leukemogenic fusion. Both of these microRNAs
directly target cell-cycle regulators and induce G1 cell-cycle arrest when
overexpressed in THP-1. We also find that the pro-differentiative mir-424 and
mir-503 downregulate the anti-differentiative mir-9 by targeting a site in its
primary transcript. Our study highlights the combinatorial effects of multiple
microRNAs within cellular systems.Comment: 45 pages 5 figure
Simple and Realistic Composite Higgs Models in Flat Extra Dimensions
We construct new composite Higgs/gauge-Higgs unification (GHU) models in flat
space that overcome all the difficulties found in the past in attempting to
construct models of this sort. The key ingredient is the introduction of large
boundary kinetic terms for gauge (and fermion) fields. We focus our analysis on
the electroweak symmetry breaking pattern and the electroweak precision tests
and show how both are compatible with each other. Our models can be seen as
effective TeV descriptions of analogue warped models. We point out that, as far
as electroweak TeV scale physics is concerned, one can rely on simple and more
flexible flat space models rather than considering their unavoidably more
complicated warped space counterparts. The generic collider signatures of our
models are essentially undistinguishable from those expected from composite
Higgs/warped GHU models, namely a light Higgs, colored fermion resonances below
the TeV scale and sizable deviations to the Higgs and top coupling.Comment: 30 figures, 9 figures; v2: minor improvements, one reference added,
version to appear in JHE
The Effective Lagrangian for Bulk Fermions in Models with Extra Dimensions
We compute the dimension 6 effective Lagrangian arising from the tree level
integration of an arbitrary number of bulk fermions in models with warped extra
dimensions. The coefficients of the effective operators are written in terms of
simple integrals of the metric and are valid for arbitrary warp factors, with
or without an infrared brane, and for a general Higgs profile. All relevant
tree level fermion effects in electroweak and flavor observables can be
computed using this effective Lagrangian.Comment: 22 pages. V2: typos corrected, matches published versio
Composite Leptoquarks at the LHC
If electroweak symmetry breaking arises via strongly-coupled physics, the
observed suppression of flavour-changing processes suggests that fermion masses
should arise via mixing of elementary fermions with composite fermions of the
strong sector. The strong sector then carries colour charge, and may contain
composite leptoquark states, arising either as TeV scale resonances, or even as
light, pseudo-Nambu-Goldstone bosons. The latter, since they are coupled to
colour, get a mass of the order of several hundred GeV, beyond the reach of
current searches at the Tevatron. The same generic mechanism that suppresses
flavour-changing processes suppresses leptoquark-mediated rare processes,
making it conceivable that the many stringent constraints may be evaded. The
leptoquarks couple predominantly to third-generation quarks and leptons, and
the prospects for discovery at LHC appear to be good. As an illustration, a
model based on the Pati-Salam symmetry is described, and its embedding in
models with a larger symmetry incorporating unification of gauge couplings,
which provide additional motivation for leptoquark states at or below the TeV
scale, is discussed.Comment: 10 pp, version to appear in JHE
Flavour Physics in the Soft Wall Model
We extend the description of flavour that exists in the Randall-Sundrum (RS)
model to the soft wall (SW) model in which the IR brane is removed and the
Higgs is free to propagate in the bulk. It is demonstrated that, like the RS
model, one can generate the hierarchy of fermion masses by localising the
fermions at different locations throughout the space. However, there are two
significant differences. Firstly the possible fermion masses scale down, from
the electroweak scale, less steeply than in the RS model and secondly there now
exists a minimum fermion mass for fermions sitting towards the UV brane. With a
quadratic Higgs VEV, this minimum mass is about fifteen orders of magnitude
lower than the electroweak scale. We derive the gauge propagator and despite
the KK masses scaling as , it is demonstrated that the
coefficients of four fermion operators are not divergent at tree level. FCNC's
amongst kaons and leptons are considered and compared to calculations in the RS
model, with a brane localised Higgs and equivalent levels of tuning. It is
found that since the gauge fermion couplings are slightly more universal and
the SM fermions typically sit slightly further towards the UV brane, the
contributions to observables such as and , from the
exchange of KK gauge fields, are significantly reduced.Comment: 33 pages, 15 figures, 5 tables; v2: references added; v3:
modifications to figures 4,5 and 6. version to appear in JHE
Mid-infrared plasmonic inductors: Enhancing inductance with meandering lines
UPNa. Departamento de IngenierÃa Eléctrica y Electrónica. Laboratorio de fotónica TERALABWe present a mid-infrared inductor that when applied to an extraordinary transmission hole array produces a strong redshift of the resonant peak accompanied by an unprecedented enlargement of the operation bandwidth. The importance of the result is twofold: from a fundamental viewpoint, the direct applicability of equivalent circuit concepts borrowed from microwaves is demonstrated, in frequencies as high as 17â€...THz upholding unification of plasmonics and microwave concepts and allowing for a simplification of structure design and analysis; in practical terms, a broadband funnelling ofinfrared radiation with fractional bandwidth and efficiency as high as 97% and 48%, respectively, is achieved through an area less than one hundredth the squared wavelength, which leads to an impressive accessible strong field localization that may be of great interest in sensing applications.Effort sponsored by Spanish Government under contracts Consolider EngineeringMetamaterials CSD2008-00066, TEC2011-28664-C01 and TEC2011-28664-C02. V.T. acknowledges funding from Universidad Pública de Navarra. P.R.-U. is sponsored by the Government of Navarra under funding program Formación de tecnólogos 055/01/11. M.N.-C. is supported by the Imperial College Junior Research Fellowship. M.B. acknowledges funding by the Spanish Government under the research contract program Ramón y Cajal RYC-2011-08221
Flavoured soft leptogenesis and natural values of the B term
We revisit flavour effects in soft leptogenesis relaxing the assumption of
universality for the soft supersymmetry breaking terms. We find that with
respect to the case in which the heavy sneutrinos decay with equal rates and
equal CP asymmetries for all lepton flavours, hierarchical flavour
configurations can enhance the efficiency by more than two orders of magnitude.
This translates in more than three order of magnitude with respect to the
one-flavour approximation. We verify that lepton flavour equilibration effects
related to off-diagonal soft slepton masses are ineffective for damping these
large enhancements. We show that soft leptogenesis can be successful for
unusual values of the relevant parameters, allowing for and for values of the washout parameter up to .Comment: 23 pages, 5 figures postscript, Minor changes to match the published
version in JHE
Heavy-light decay topologies as a new strategy to discover a heavy gluon
We study the collider phenomenology of the lightest Kaluza-Klein excitation
of the gluon, G*, in theories with a warped extra dimension. We do so by means
of a two-site effective lagrangian which includes only the lowest-lying spin-1
and spin-1/2 resonances. We point out the importance of the decays of G* to one
SM plus one heavy fermion, that were overlooked in the previous literature. It
turns out that, when kinematically allowed, such heavy-light decays are
powerful channels for discovering the G*. In particular, we present a
parton-level Montecarlo analysis of the final state Wtb that follows from the
decay of G* to one SM top or bottom quark plus its heavy partner. We find that
at \sqrt{s} = 7 TeV and with 10 fb^{-1} of integrated luminosity, the LHC can
discover a KK gluon with mass in the range M_{G*} = (1.8 - 2.2) TeV if its
coupling to a pair of light quarks is g_{G*qqbar} = (0.2-0.5) g_3. The same
process is also competitive for the discovery of the top and bottom partners as
well. We find, for example, that the LHC at \sqrt{s} = 7 TeV can discover a 1
TeV KK bottom quark with an integrated luminosity of (5.3 - 0.61) fb^{-1} for
g_{G*qqbar} = (0.2-0.5) g_3.Comment: 36 pages, 13 figures. v2: a few typos corrected, comments added,
version published in JHE
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