875 research outputs found
Collider phenomenology of Higgs bosons in Left-Right symmetric Randall-Sundrum models
We investigate the collider phenomenology of a left-right symmetric
Randall-Sundrum model with fermions and gauge bosons in the bulk. We find that
the model is allowed by precision electroweak data as long as the ratio of the
(unwarped) Higgs vev to the curvature scale is . In that region
there can be substantial modifications to the Higgs properties. In particular,
the couplings to and are reduced, the coupling to gluons is enhanced,
and the coupling to can receive shifts in either direction. The
Higgs mass bound from LEP II data can potentially be relaxed to GeV.Comment: 21 pages, 11 figures. Minor changes to numerics; replaced with
published versio
5D UED: Flat and Flavorless
5D UED is not automatically minimally flavor violating. This is due to flavor
asymmetric counter-terms required on the branes. Additionally, there are likely
to be higher dimensional operators which directly contribute to flavor
observables. We document a mostly unsuccessful attempt at utilizing
localization in a flat extra dimension to resolve these flavor constraints
while maintaining KK-parity as a good quantum number. It is unsuccessful
insofar as we seem to be forced to add brane operators in such a way as to
precisely mimic the effects of a double throat warped extra dimension. In the
course of our efforts, we encounter and present solutions to a problem common
to many extra dimensional models in which fields are "doubly localized:"
ultra-light modes. Under scrutiny, this issue seems tied to an intrinsic
tension between maintaining Kaluza-Klein parity and resolving mass hierarchies
via localization.Comment: 27 pages, 6 figure
Detecting a Boosted Diboson Resonance
New light scalar particles in the mass range of hundreds of GeV, decaying
into a pair of bosons can appear in several extensions of the SM. The
focus of collider studies for such a scalar is often on its direct production,
where the scalar is typically only mildly boosted. The observed are
therefore well-separated, allowing analyses for the scalar resonance in a
standard fashion as a low-mass diboson resonance. In this work we instead focus
on the scenario where the direct production of the scalar is suppressed, and it
is rather produced via the decay of a significantly heavier (a few TeV mass)
new particle, in conjunction with SM particles. Such a process results in the
scalar being highly boosted, rendering the 's from its decay merged. The
final state in such a decay is a "fat" jet, which can be either four-pronged
(for fully hadronic decays), or may be like a jet, but with leptons
buried inside (if one of the decays leptonically). In addition, this fat
jet has a jet mass that can be quite different from that of the /Higgs/top
quark-induced jet, and may be missed by existing searches. In this work, we
develop dedicated algorithms for tagging such multi-layered "boosted dibosons"
at the LHC. As a concrete application, we discuss an extension of the standard
warped extra-dimensional framework where such a light scalar can arise. We
demonstrate that the use of these algorithms gives sensitivity in mass ranges
that are otherwise poorly constrained.Comment: 33 pages, 13 figure
Dedicated Strategies for Triboson Signals from Cascade Decays of Vector Resonances
New colorless electroweak (EW) charged spin-1 particles with mass of a few
TeV arise in numerous extensions of the Standard Model (SM). Decays of such a
vector into a pair of SM particles, either fermions or EW bosons, are well
studied. Many of these models have an additional scalar, which can lead to (and
even dominate in certain parameter regions) a novel decay channel for the heavy
vector particles instead - into a SM EW boson and the scalar, which
subsequently decays into a SM EW boson pair. In this work, we focus on the
scalar being relatively heavy, roughly factor of two lighter than the vector
particles, rendering its decay products well separated. Such a cascade decay
results in a final state with three isolated bosons. We argue that for this
"triboson" signal the existing diboson searches are not quite optimal due to
combinatorial ambiguity for three identical bosons, and in addition, due to a
relatively small signal cross-section determined by the heaviness of the
decaying vector particle. In order to isolate the signal, we demonstrate that
tagging all three bosons, followed by use of the full triboson invariant mass
distribution as well as that of appropriate subsets of dibosons, is well
motivated. We develop these general strategies in detail within the context of
a specific class of models that are based on extensions of the standard warped
extra-dimensional scenario. We also point out that a similar analysis would
apply to models with an enlarged EW gauge sector in four dimensions, even if
they involve a different Lorentz structure for the relevant couplings
Searching for the Kaluza-Klein Graviton in Bulk RS Models
The best-studied version of the RS1 model has all the Standard Model
particles confined to the TeV brane. However, recent variants have the Standard
Model fermions and gauge bosons located in the bulk five-dimensional spacetime.
We study the potential reach of the LHC in searching for the lightest KK
partner of the graviton in the most promising such models in which the
right-handed top is localized very near the TeV brane and the light fermions
are localized near the Planck brane. We consider both detection and the
establishment of the spin-2 nature of the resonance should it be found.Comment: 17 pages, 6 figures - JHEP published version, figures added,
branching ratio correcte
Novel candidate genes underlying extreme trophic specialization in Caribbean pupfishes
The genetic changes responsible for evolutionary transitions from generalist to specialist phenotypes are poorly understood. Here we examine the genetic basis of craniofacial traits enabling novel trophic specialization in a sympatric radiation of Cyprinodon pupfishes endemic to San Salvador Island, Bahamas. This recent radiation consists of a generalist species and two novel specialists: a small-jawed "snail-eater" and a large-jawed "scale-eater." We genotyped 12 million single nucleotide polymorphisms (SNPs) by whole-genome resequencing of 37 individuals of all three species from nine populations and integrated genome-wide divergence scans with association mapping to identify divergent regions containing putatively causal SNPs affecting jaw size-the most rapidly diversifying trait in this radiation. A mere 22 fixed variants accompanied extreme ecological divergence between generalist and scale-eater species. We identified 31 regions (20 kb) containing variants fixed between specialists that were significantly associated with variation in jaw size which contained 11 genes annotated for skeletal system effects and 18 novel candidate genes never previously associated with craniofacial phenotypes. Six of these 31 regions showed robust signs of hard selective sweeps after accounting for demographic history. Our data are consistent with predictions based on quantitative genetic models of adaptation, suggesting that the effect sizes of regions influencing jaw phenotypes are positively correlated with distance between fitness peaks on a complex adaptive landscape
Low-scale warped extra dimension and its predilection for multiple top quarks
Within warped extra dimension models that explain flavor through geometry,
flavor changing neutral current constraints generally force the Kaluza-Klein
scale to be above many TeV. This creates tension with a natural electroweak
scale. On the other hand, a much lower scale compatible with precision
electroweak and flavor changing neutral current constraints is allowed if we
decouple the Kaluza-Klein states of Standard Model gauge bosons from light
fermions bulk mass parameters). The main
signature for this approach is four top quark production via the Kaluza-Klein
excitations' strong coupling to top quarks. We study single lepton, like-sign
dilepton, and trilepton observables of four-top events at the Large Hadron
Collider. The like-sign dilepton signature typically has the largest discovery
potential for a strongly coupled right-handed top case (M_{KK} \sim 2-2.5
\TeV), while single lepton is the better when the left-handed top couples most
strongly (M_{KK} \sim 2 \TeV). We also describe challenging lepton-jet
collimation issues in the like-sign dilepton and trilepton channels. An
alternative single lepton observable is considered which takes advantage of the
many bottom quarks in the final state. Although searches of other particles may
compete, we find that four top production via Kaluza-Klein gluons is most
promising in a large region of this parameter space.Comment: 35 pages, 8 figures. discussions improved, references adde
An A4 flavor model for quarks and leptons in warped geometry
We propose a spontaneous A4 flavor symmetry breaking scheme implemented in a
warped extra dimensional setup to explain the observed pattern of quark and
lepton masses and mixings. The main advantages of this choice are the
explanation of fermion mass hierarchies by wave function overlaps, the
emergence of tribimaximal neutrino mixing and zero quark mixing at the leading
order and the absence of tree-level gauge mediated flavor violations. Quark
mixing is induced by the presence of bulk flavons, which allow for cross-brane
interactions and a cross-talk between the quark and neutrino sectors, realizing
the spontaneous symmetry breaking pattern A4 --> nothing first proposed in
[X.G.\,He, Y.Y.\,Keum, R.R.\,Volkas, JHEP{0604}, 039 (2006)]. We show that the
observed quark mixing pattern can be explained in a rather economical way,
including the CP violating phase, with leading order cross-interactions, while
the observed difference between the smallest CKM entries V_{ub} and V_{td} must
arise from higher order corrections. We briefly discuss bounds on the
Kaluza-Klein scale implied by flavor changing neutral current processes in our
model and show that the residual little CP problem is milder than in flavor
anarchic models.Comment: 34 pages, 2 figures; version published in JHE
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
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