614 research outputs found
Discovering the composite Higgs through the decay of a heavy fermion
A possible composite nature of the Higgs could be revealed at the early stage
of the LHC, by analyzing the channels where the Higgs is produced from the
decay of a heavy fermion. The Higgs production from a singly-produced heavy
bottom, in particular, proves to be a promising channel. For a value \lambda=3
of the Higgs coupling to a heavy bottom, for example, we find that, considering
a 125 GeV Higgs which decays into a pair of b-quarks, a discovery is possible
at the 8 TeV LHC with 30 fb^{-1} if the heavy bottom is lighter than roughly
530 GeV (while an observation is possible for heavy bottom masses up to 650
GeV). Such a relatively light heavy bottom is realistic in composite Higgs
models of the type considered and, up to now, experimentally allowed. At
\sqrt{s}=14 TeV the LHC sensitivity on the channel increases significantly.
With \lambda=3 a discovery can occur, with 100 fb^{-1}, for heavy bottom masses
up to 1040 GeV. In the case the heavy bottom was as light as 500 GeV, the 14
TeV LHC would be sensitive to the measure of the \lambda\ coupling in basically
the full range \lambda>1 predicted by the theory.Comment: 25 pp. v2: Minor changes. v3: Version accepted for publication in
JHEP. v4: typos fixe
On dimensional regularization of sums
We discuss a systematic way to dimensionally regularize divergent sums
arising in field theories with an arbitrary number of physical compact
dimensions or finite temperature. The method preserves the same symmetries of
the action as the conventional dimensional regularization and allows an easy
separation of the regulated divergence from the finite term that depends on the
compactification radius (temperature).Comment: 22 pages, 1 figur
Warped/Composite Phenomenology Simplified
This is the first of two papers aimed at economically capturing the collider phenomenology of warped extra dimensions with bulk Standard Model fields, where the hierarchy problem is solved non-supersymmetrically. This scenario is related via the AdS/CFT correspondence to that of partial compositeness of the Standard Model. We present a purely four-dimensional, two-sector effective field theory describing the Standard Model fields and just their first Kaluza-Klein/composite excitations. This truncation, while losing some of the explanatory power and precision of the full higher-dimensional warped theory, greatly simplifies phenomenological considerations and computations. We describe the philosophy and explicit construction of our two-sector model, and also derive formulas for residual Higgs fine tuning and electroweak and flavor precision variables to help identify the most motivated parts of the parameter space. We highlight several of the most promising channels for LHC exploration. The present paper focusses on the most minimal scenario, while the companion paper addresses the even richer phenomenology of the minimal scenario of precision gauge coupling unification
Partially Supersymmetric Composite Higgs Models
We study the idea of the Higgs as a pseudo-Goldstone boson within the
framework of partial supersymmetry in Randall-Sundrum scenarios and their CFT
duals. The Higgs and third generation of the MSSM are composites arising from a
strongly coupled supersymmetric CFT with global symmetry SO(5) spontaneously
broken to SO(4), whilst the light generations and gauge fields are elementary
degrees of freedom whose couplings to the strong sector explicitly break the
global symmetry as well as supersymmetry. The presence of supersymmetry in the
strong sector may allow the compositeness scale to be raised to ~10 TeV without
fine tuning, consistent with the bounds from precision electro-weak
measurements and flavour physics. The supersymmetric flavour problem is also
solved. At low energies, this scenario reduces to the "More Minimal
Supersymmetric Standard Model" where only stops, Higgsinos and gauginos are
light and within reach of the LHC.Comment: 28 pages. v2 minor changes and Refs. adde
Cosmological Consequences of Nearly Conformal Dynamics at the TeV scale
Nearly conformal dynamics at the TeV scale as motivated by the hierarchy
problem can be characterized by a stage of significant supercooling at the
electroweak epoch. This has important cosmological consequences. In particular,
a common assumption about the history of the universe is that the reheating
temperature is high, at least high enough to assume that TeV-mass particles
were once in thermal equilibrium. However, as we discuss in this paper, this
assumption is not well justified in some models of strong dynamics at the TeV
scale. We then need to reexamine how to achieve baryogenesis in these theories
as well as reconsider how the dark matter abundance is inherited. We argue that
baryonic and dark matter abundances can be explained naturally in these setups
where reheating takes place by bubble collisions at the end of the strongly
first-order phase transition characterizing conformal symmetry breaking, even
if the reheating temperature is below the electroweak scale GeV. We
also discuss inflation as well as gravity wave smoking gun signatures of this
class of models.Comment: 22 pages, 7 figure
The fate of the zero mode of the five-dimensional kink in the presence of gravity
We investigate what becomes of the translational zero-mode of a
five-dimensional domain wall in the presence of gravity, studying the scalar
perturbations of a thick gravitating domain wall with AdS asymptotics and a
well-defined zero-gravity limit. Our analysis reveals the presence of a wide
resonance which can be seen as a remnant of the translational zero-mode present
in the domain wall in the absence of gravity and which ensures a continuous
change of the physical quantities (such as e.g. static potential between
sources) when the Planck mass is sent to infinity. Provided that the thickness
of the wall is much smaller than the AdS radius of the space-time, the
parameters of this resonance do not depend on details of the domain wall's
structure, but solely on the geometry of the space-time.Comment: 29 pages, 4 figures; v2: 2 machine-generated typos in the
introduction correcte
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
Gaugephobic Higgs Signals at the LHC
The Gaugephobic Higgs model provides an interpolation between three different
models of electroweak symmetry breaking: Higgsless models, Randall-Sundrum
models, and the Standard Model. At parameter points between the extremes,
Standard Model Higgs signals are present at reduced rates, and Higgsless
Kaluza-Klein excitations are present with shifted masses and couplings, as well
as signals from exotic quarks necessary to protect the Zbb coupling. Using a
new implementation of the model in SHERPA, we show the LHC signals which
differentiate the generic Gaugephobic Higgs model from its limiting cases.
These are all signals involving a Higgs coupling to a Kaluza-Klein gauge boson
or quark. We identify the clean signal mediated by a
Kaluza-Klein W, which can be present at large rates and is enhanced for even
Kaluza-Klein numbers. Due to the very hard lepton coming from the W decay, this
signature has little background, and provides a better discovery channel for
the Higgs than any of the Standard Model modes, over its entire mass range. A
Higgs radiated from new heavy quarks also has large rates, but is much less
promising due to very high multiplicity final states.Comment: 16 pages, 8 figure
Higgs as a Holographic Pseudo-Goldstone Boson
The AdS/CFT correspondence allows to relate 4D strongly coupled theories to
weakly coupled theories in 5D AdS. We use this correspondence to study a
scenario in which the Higgs appears as a composite pseudo-Goldstone boson (PGB)
of a strongly coupled theory. We show how a non-linearly realized global
symmetry protects the Higgs mass and guarantees the absence of quadratic
divergences at any loop order. The gauge and Yukawa interactions for the PGB
Higgs are introduced in a simply way in the 5D AdS theory, and their one-loop
contributions to the Higgs potential are calculated using perturbation theory.
These contributions are finite, giving a squared-mass to the Higgs which is
one-loop smaller than the mass of the first Kaluza-Klein state. We also show
that if the symmetry breaking is caused by boundary conditions in the extra
dimension, the PGB Higgs corresponds to the fifth component of the bulk gauge
boson. To make the model fully realistic, a tree-level Higgs quartic coupling
must be induced. We present a possible mechanism to generate it and discuss the
conditions under which an unwanted large Higgs mass term is avoided.Comment: 31 pages, 6 figure
Discovery potential of top-partners in a realistic composite Higgs model with early LHC data
Composite Higgs models provide a natural, non-supersymmetric solution to the
hierarchy problem. In these models, one or more sets of heavy top-partners are
typically introduced. Some of these new quarks can be relatively light, with a
mass of a few hundred GeV, and could be observed with the early LHC collision
data expected to be collected during 2010. We analyse in detail the collider
signatures that these new quarks can produce. We show that final states with
two (same-sign) or three leptons are the most promising discovery channels.
They can yield a 5 sigma excess over the Standard Model expectation already
with the 2010 LHC collision data. Exotic quarks of charge 5/3 are a distinctive
feature of this model. We present a new method to reconstruct their masses from
their leptonic decay without relying on jets in the final state.Comment: 28 pages 11 Figures 7 Tables, minor changes, added references,
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