1,070 research outputs found
An Improved Model of Direct Gauge Mediation
We present a new, improved model of gauge mediation of dynamical SUSY Breaking: the model does not have gauge messengers or TeV scalars charged under the Standard Model (SM), thus avoiding the problem of negative (mass) for supersymmetric SM (SSM) scalars faced by some earlier models. The gauge mediation is direct, i.e., the messengers which communicate SUSY breaking to the SSM fields carry quantum numbers of the gauge group which breaks SUSY. These messenger fields couple to a modulus field. The model has a very simple particle content: the modulus and the messengers are the only chiral superfields (other than the SSM fields) in the model. The inverted hierarchy mechanism is used to generate a local SUSY breaking minimum for the modulus field in a perturbative regime thus making the model calculable
LHC Signals from Cascade Decays of Warped Vector Resonances
Recently (arXiv:1608.00526), a new framework for warped higher-dimensional
compactifications with "bulk" standard model (SM) was proposed: in addition to
the UV (Planck scale) and IR (a couple of TeV) branes, there is an intermediate
brane, taken to be around 10 TeV. The SM matter and Higgs fields propagate from
the UV brane down to this intermediate brane only, while gauge and gravity
fields propagate in the entire bulk. Such a configuration renders the lightest
gauge Kaluza-Klein (KK) states within LHC reach, simultaneously satisfying
flavor and CP constraints. In addition, the usual leading decay modes of the
lightest KK gauge bosons into top and Higgs bosons are suppressed. This effect
permits erstwhile subdominant channels to become significant. These include
flavor-universal decays to SM fermions and Higgs bosons, and a novel channel -
decay to a radion and a SM gauge boson, followed by radion decay to a pair of
SM gauge bosons. In this work, we first delineate the parameter space where the
above mentioned cascade decay of gauge KK particles dominates, and thereby can
be the discovery mode at the LHC. We then perform a detailed analysis of the
LHC signals from this model, finding that 300/fb suffices for evidence of
KK-gluon in tri-jet, jet + di-photon and jet + di-boson channels. However, KK
photon in photon + di-jet, and KK-W in leptonic W + di-jet require 3000/fb. The
crucial feature of this decay chain is a "double" resonance, i.e. 3-particle
and 2-particle invariant mass peaks, corresponding to the KK gauge boson and
the radion respectively.Comment: 50 page
Can multi-TeV (top and other) squarks be natural in gauge mediation?
We investigate whether multi-TeV (1-3 TeV) squarks can be natural in models
of gauge mediated SUSY breaking. The idea is that for some boundary condition
of the scalar (Higgs and stop) masses, the Higgs (mass), evaluated at the
renormalization scale GeV, is not very sensitive to (boundary
values of) the scalar masses (this has been called ``focussing'' in recent
literature). Then, the stop masses can be multi-TeV without leading to
fine-tuning in electroweak symmetry breaking. {\em Minimal} gauge mediation
does {\em not} lead to this focussing (for all values of and the
messenger scale): the (boundary value of) the Higgs mass is too small compared
to the stop masses. Also, in minimal gauge mediation, the gaugino masses are of
the same order as the scalar masses so that multi-TeV scalars implies multi-TeV
gauginos (especially gluino) leading to fine-tuning. We discuss ideas to {\em
increase} the Higgs mass relative to the stop masses (so that focussing can be
achieved) and also to {\em suppress} gaugino masses relative to scalar masses
(or to modify the gaugino mass relations) in {\em non-minimal} models of gauge
mediation -- then multi-TeV (top and other) squarks can be natural. Specific
models of gauge mediation which incorporate these ideas and thus have squarks
(and in some cases, the gluino) heavier than a TeV without resulting in
fine-tuning are also studied and their collider signals are contrasted with
those of other models which have multi-TeV squarks.Comment: LaTeX, 29 pages, 9 eps figures. Replacing an earlier version. In
version 3, some references and a minor comment have been added and typos have
been correcte
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
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
Matter-gravity interaction in a multiply warped braneworld,
The role of a bulk graviton in predicting the signature of extra dimensions
through collider-based experiments is explored in the context of a multiply
warped spacetime. In particular it is shown that in a doubly warped braneworld
model, the presence of the sixth dimension, results in enhanced concentration
of graviton Kaluza Klein (KK) modes compared to that obtained in the usual
5-dimensional Randall-Sundrum model. Also, the couplings of these massive
graviton KK modes with the matter fields on the visible brane turn out to be
appreciably larger than that in the corresponding 5- dimensional model. The
significance of these results are discussed in the context of KK graviton
search at the Large Hadron Collider (LHC).Comment: 13 pages, 2 table
Conformal Technicolor
We point out that the flavor problem in theories with dynamical electroweak
symmetry breaking can be effectively decoupled if the physics above the TeV
scale is strongly conformal, and the electroweak order parameter has a scaling
dimension d = 1 + epsilon with epsilon \simeq 1/few. There are many
restrictions on small values of epsilon: for epsilon << 1, electroweak symmetry
breaking requires a fine-tuning similar to that of the standard model; large-N
conformal field theories (including those obtained from the AdS/CFT
correspondence) require fine-tuning for d < 2; `walking technicolor' theories
cannot have d < 2, according to gap equation analyses. However, strong small-N
conformal field theories with epsilon \simeq 1/few avoid all these constraints,
and can give rise to natural dynamical electroweak symmetry breaking with a top
quark flavor scale of order 10^{1/epsilon} TeV, large enough to decouple
flavor. Small-N theories also have an acceptably small Peskin-Takeuchi S
parameter. This class of theories provides a new direction for dynamical
electroweak symmetry breaking without problems from flavor or electroweak
precision tests. A possible signal for these theories is a prominent scalar
resonance below the TeV scale with couplings similar to a heavy standard model
Higgs.Comment: 26 pages + References. Slight wording changes. Version appearing in
JHE
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