160 research outputs found
A holographic composite Higgs model
If the Higgs boson has a composite nature, it might be the 4-dimensional
hologram of a gauge field living in a warped extra dimension. In this talk I
discuss a minimal, calculable model that passes all electroweak precision
tests, included that from Z->bb, and gives a natural account of the electroweak
symmetry breaking.Comment: 4 pages, talk given at IFAE 2006, Pavia, Italy, April 19-21 200
New Physics at the LHC: Strong vs Weak symmetry breaking
What kind of New Physics, if any, we expect to discover at the LHC? I will
try to address this formidable question by re-formulating it as follows: is the
breaking of the electroweak symmetry strong or weak ?Comment: Talk given at IFAE 2009, Bari, Italy, 15-17 April 200
The Supersymmetric Flavor Problem for Heavy First-Two Generation Scalars at Next-to-Leading Order
We analyze in detail the constraints on SUSY-model parameters obtained from
K-Kbar mixing in the hypothesis of a splitted SUSY spectrum. FCNC contributions
from gluino-squark-quark interactions are studied in the so-called mass
insertion approximation. We present boundaries on mass insertions and on SUSY
mass scales. We improve previous results by including the NLO-QCD corrections
to Delta S=2 effective Hamiltonian and the complete set of B-parameters for the
evaluation of hadronic matrix elements.
A full set of magic-numbers, that can be used for further analyses of these
models, is also given. We find that the inclusion of NLO-QCD corrections and
the B-parameters change the results obtained at LO and in the Vacuum Insertion
Approximation by an amount of about 25-35%.Comment: 22 Latex pages, 5 figures; Figs. 1,2 redrawn for K=0.22, section 4.1
revisited, references corrected. Submitted to European Journal of Physics
Dispersion Relations for Electroweak Observables in Composite Higgs Models
We derive dispersion relations for the electroweak oblique observables
measured at LEP in the context of composite Higgs models. It is
shown how these relations can be used and must be modified when modeling the
spectral functions through a low-energy effective description of the strong
dynamics. The dispersion relation for the parameter is then used
to estimate the contribution from spin-1 resonances at the 1-loop level.
Finally, it is shown that the sign of the contribution to the
parameter from the lowest-lying spin-1 states is not necessarily positive
definite, but depends on the energy scale at which the asymptotic behavior of
current correlators is attained.Comment: 34 pages, 4 figures. v2: a few minor changes, typos corrected, list
of references revise
One-loop effects from spin-1 resonances in Composite Higgs models
We compute the 1-loop correction to the electroweak observables from spin-1
resonances in SO(5)/SO(4) composite Higgs models. The strong dynamics is
modeled with an effective description comprising the Nambu-Goldstone bosons and
the lowest-lying spin-1 resonances. A classification is performed of the
relevant operators including custodially-breaking effects from the gauging of
hypercharge. The 1-loop contribution of the resonances is extracted in a
diagrammatic approach by matching to the low-energy theory of Nambu-Goldstone
bosons. We find that the correction is numerically important in a significant
fraction of the parameter space and tends to weaken the bounds providing a
negative shift to the S parameter.Comment: 45 pages, 13 figures. v2: minor corrections, conclusions unchanged.
v3: two diagrams in Fig.13 correctly redraw
Top Compositeness and Precision Unification
The evolution of Standard Model gauge couplings is studied in a
non-supersymmetric scenario in which the hierarchy problem is resolved by Higgs
compositeness above the weak scale. It is argued that massiveness of the top
quark combined with precision tests of the bottom quark imply that the
right-handed top must also be composite. If, further, the Standard Model gauge
symmetry is embedded into a simple subgroup of the unbroken composite-sector
flavor symmetry, then precision coupling unification is shown to occur
at~10^{15} GeV, to a degree comparable to supersymmetric unification.Comment: v2: few extra comments added; slightly shorter version published in
PR
Higgs pair production in vector-boson fusion at the LHC and beyond
The production of pairs of Higgs bosons at hadron colliders provides unique
information on the Higgs sector and on the mechanism underlying electroweak
symmetry breaking (EWSB). Most studies have concentrated on the gluon fusion
production mode which has the largest cross section. However, despite its small
production rate, the vector-boson fusion channel can also be relevant since
even small modifications of the Higgs couplings to vector bosons induce a
striking increase of the cross section as a function of the invariant mass of
the Higgs boson pair. In this work, we exploit this unique signature to propose
a strategy to extract the quartic coupling and provide model-independent
constraints on theories where EWSB is driven by new strong interactions. We
take advantage of the higher signal yield of the final state
and make extensive use of jet substructure techniques to reconstruct signal
events with a boosted topology, characteristic of large partonic energies,
where each Higgs boson decays to a single collimated jet . Our results
demonstrate that the coupling can be measured with 45% (20%) precision
at the LHC for 300 (3000) fb, while a 1% precision can be
achieved at a 100 TeV collider.Comment: Updated to match published version in EPJC and fixed typo in Tab. 10
(column labels a & b were swapped
Contextualizing the Higgs at the LHC
Recent excesses across different search modes of the collaborations at the
LHC seem to indicate the presence of a Higgs-like scalar particle at 125 GeV.
Using the current data sets, we review and update analyses addressing the
extent to which this state is compatible with the Standard Model, and provide
two contextual answers for how it might instead fit into alternative scenarios
with enlarged electroweak symmetry breaking sectors.Comment: Contribution to the proceedings of PLHC 2012, Vancouver, BC, June
4-9, 201
Z', Z_KK, Z* and all that: current bounds and theoretical prejudices on heavy neutral vector bosons
I review the current experimental bounds and theoretical predictions for
different kinds of heavy neutral vector bosons.Comment: Talk given at: V Workshop Italiano sulla fisica p-p ad LHC, Perugia,
Italy, 30 Jan. - 2 Feb. 200
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