44 research outputs found
Z-peaked excess from heavy gluon decays to vector-like quarks
A 3 sigma excess has been recently announced by ATLAS in events with Z-peaked
dilepton pairs, jets, and large transverse missing energy. We interpret this
finding in the context of composite Higgs / RS theories. We find that composite
Higgs theories with custodial symmetry protection to the coupling
predict a significant contribution to (and to ) final states
coming from heavy gluon decays to pairs of bottom-partner vector-like quarks.
The heavy gluon to vector-like quarks signal is largely accepted by the ATLAS
selection if one of the boson in the final state decays leptonically
and the other to neutrinos. For a bottom partner of 900 GeV, we find that
the ATLAS excess can be reproduced by composite Higgs models, in an
experimentally allowed parameter space, for heavy gluon masses roughly in a
range 1.87 - 2.15 TeV and for heavy gluon couplings to light quarks within
. We briefly discuss the implication of this result for
future experimental tests.Comment: 23 pp. v2: minor changes, references adde
Early discovery of top partners and test of the Higgs nature
Top partners from a new strong sector can be discovered soon, at the 8 TeV
LHC, by analyzing their single production, which exhibits a large enhancement
in the cross section compared to the analogous productions of bottom partners
and exotic quarks. We analyze the subsequent decay of the top partners into a
125 GeV Higgs. This channel proves to be very promising for both the discovery
of top partners and a test of the Higgs sector. For a reference value
of the Higgs coupling to the top partner, we could have
a discovery (observation) at the 8 TeV LHC, with 30 fb, for top partner
masses up to 760 (890) GeV. If the LHC and Tevatron excesses near 125 GeV are
really due to a composite Higgs, naturalness arguments demand top partners
below TeV. Our results highlight thus that the 8 TeV LHC already has a
large sensitivity on probing the composite Higgs hypothesis. The LHC reach is
even wider at TeV. With the LHC with 100
fb can observe (at 5) a Higgs from a top partner decay for
masses of this latter up to GeV. In the case the top partner was
as light as GeV, the 14 TeV LHC would be sensitive to the measure
of the coupling in basically the full range
predicted by the theory.Comment: 9 pp. Minor changes. Version to appear in PRD. arXiv admin note:
substantial text overlap with arXiv:1204.046
A New Strategy to Discover Heavy Colored Vectors at the Early LHC
We perform a study of the LHC discovery reach on a heavy gluon (G*) and heavy
fermions (top and bottom excitations), coming from a new composite sector. We
find that heavy fermion resonances have a great impact on the composite gluon
phenomenology. If the composite gluon is heavier than composite fermions, as
flavor observables seem to suggest, the search in the channel where G* decays
into a heavy fermion plus its Standard Model partner is very promising, with
the possibility for both the G* and heavy fermions to be discovered at the
early stage of the LHC. The channel offers also the possibility to extract
important information on model parameters, such as the top degree of
compositeness.Comment: Presented at IFAE 2011, Incontri di Fisica delle Alte Energie,
Perugia, Italy, 27-29 April. 4 pages, 3 figures. References adde
New W-prime signals at the LHC
We study the phenomenology in composite Higgs/ warped extra
dimensional models focusing on the effect of fermionic resonances at 1
TeV. After deriving the existing bounds from the current LHC-8 analyses, we
highlight the most promising signatures for discovery at the 14 TeV
LHC. We find in particular very promising the study of decay modes into
vector-like top partners, specifically the decay into a doublet of custodian
heavy fermions, , and the decay into a heavy fermion plus a
Standard Model quark. We perform a detailed parton level analysis of the
channel in the same-sign dilepton final state,
finding that it is a very promising signature to test the region at high
mass, TeV, and of the mode, that is
one of the best channels to test the intermediate mass region and that,
already with the LHC-8 data, could extend the present exclusion bounds.Comment: 25 pp. v2: minor changes, references added, version to appear in
Phys. Rev.
Diphoton Resonances at the LHC
We review the current status of searches for new physics beyond the Standard
Model in the diphoton channel at the LHC and estimate the reach with future
collected data. We perform a model independent analysis based on an effective
field theory approach and different production mechanisms. As an illustrative
example, we apply our results to a scenario of minimal composite dynamics.Comment: 13 pages, 3 figures; invited review for MPLA; journal versio
Charged resonances and MDM bound states at a multi-TeV muon collider
A multi-TeV muon collider proves to be very efficient not only for the search
for new heavy neutral particles, but also for the discovery of charged bosons
of the type. We find that, by analyzing the associated production
with a Standard Model W, charged resonances can be probed directly up to
multi-TeV mass values close to the collision energy, and for very small
couplings with the SM fermions, of the order of times the SM
weak coupling. Additionally, charged bound states of WIMP Minimal Dark Matter,
specifically a Majorana fermionic 5-plet, can be discovered with low statistics
by running above the kinematic threshold, at a center-of-mass energy just
slightly above the mass of the MDM bound state. This opens up a very
interesting possibility for the discovery of WIMPs, complementary to the search
for the resonant production of the neutral MDM bound state component, which
relies on an on-peak search. For 5-plet MDM, indeed, the proposed search
strategy is more efficient than the WIMP searches based on mono-X, missing-mass
and disappearing tracks signatures.Comment: v2: several improvements and additions, ref.s added. 10 pages, 6
figures, 1 tabl
constraints on composite Higgs models with LR parity
We analyze the bounds on the spectrum of composite Higgs models (CHM) that
come from flavor observables, by means of simple two-site effective
Lagrangians, which incorporate a custodial symmetry and a Left-Right parity and
which could also be adopted in further phenomenological studies on CHM. We
derive, in particular, an important constraint on the masses of the partners, which does not depend on the flavor structure of the sector
beyond the SM. This bound is obtained from the "infrared" contribution to induced by the flavor-conserving effective vertex . We
find that the presence of a custodial symmetry can play a role in protecting
this effective coupling and, as a consequence, in attenuating the constraint,
which, however, remains of the order of 1 TeV. In addition to this bound, we
calculate the constraints from the "ultraviolet" contribution to , induced by loops of heavy fermions, and to .Comment: 35 pp. Version to appear in PR
Phenomenology of heavy fermion and vector resonances in composite Higgs models
In this project we study the phenomenology of models where the Higgs is a
bound state of a strongly interacting dynamics at the TeV scale and we assess
the LHC potential to discover new heavy colored states. In the first part of
the thesis we analyze the bounds on the spectrum of Composite Higgs Models
(CHM) that come from flavor observables. In the second part we propose a novel
strategy to discover a heavy gluon () and heavy fermions at the LHC. We do
so by means of simple two-site effective Lagrangians, which could also be used
in further phenomenological studies on CHM. From the analysis of the bounds on
the CHM spectrum, we derive an important constraint on the masses of the heavy
fermions which does not depend on the flavor structure of the sector beyond the
SM. This bound is obtained from the infrared contribution to
induced by the flavor-conserving effective vertex . We find that the
presence of a custodial symmetry can play a role in protecting this effective
coupling. Studying the heavy colored vectors phenomenology, we find that heavy
composite fermions have a great impact on the phenomenology of heavy composite
gluon at the LHC. If the composite gluon is heavier than the composite
fermions, as flavor observables seem to suggest, the search in the channels
where decays into one heavy fermion plus its Standard Model partner is
very promising, with the possibility for both the and heavy fermions to
be discovered at the early stage of the LHC. These channels offer also the
possibility to extract important information on model's parameters, such as the
top degree of compositeness.Comment: Ph.D. Thesis (Advisor: Roberto Contino). Dec 2011. 110 pp. Graduation
date added. References adde