198 research outputs found
Possible experimental signatures at the LHC of strongly interacting electro-weak symmetry breaking
If electro-weak symmetry is broken by a new strongly interacting sector, new
physics will probably manifest itself in gauge boson scattering at the LHC. The
relevant dynamics is well described in terms of an effective lagrangian. We
discuss the probable size of the coefficients of the relevant operators under a
combination of model-independent constraints and reasonable assumptions based
on two models of the strongly interacting sector. We compare these values with
LHC sensitivity and argue that they will be too small to be seen. Therefore,
the presence of vector and scalar resonances required by unitarity will be the
only characteristic signature. We analyze the most likely masses and widths of
these resonances.Comment: 14 pages, pdftex, 5 figures, improved discussion of bounds, 1
footnote remove
Telling the spin of the "Higgs boson" at the LHC
We assume that the Higgs boson or a possible resonance---playing its role in
strongly interacting models of electroweak symmetry breaking---has been
discovered at the LHC and propose a search strategy to determine its spin based
on two simple asymmetries in the ZZ, W+W- and t t-bar decays channels. We
consider some benchmark values for its mass (in the interval from 182 GeV/c^2
to 1 TeV/c^2) and discuss the relative advantages of the different decay
processes. A full analysis, including the background, is given. For a
center-of-mass energy of 14 TeV, we find that the lowest integrated luminosity
required to discriminate between the different spins is, depending on the
process and the resonance mass, between 40 fb^{-1} and 250 fb^{-1}.Comment: 17 pages, 3 figure
Constraints on top quark non-standard interactions from Higgs and production cross sections
We identify the differential cross sections for production and the
total cross section for Higgs production through gluon fusion as the processes
in which the two effective operators describing the leading non-standard
interactions of the top quark with the gluon can be disentangled and studied in
an independent fashion. Current data on the Higgs production and the differential cross section provide limits comparable,
but not more stringent, than those from the total cross sections
measurements at the LHC and Tevatron, where however the two operators enter on
the same footing and can only be constrained together. Given the present
uncertainties, we find that the most stringent bounds are provided by a
combination of data on the total cross sections together with those
from the Higgs production. We conclude by stating the (modest) reduction in the
uncertainties necessary to provide more stringent limits by means of the Higgs
production and differential cross section observables at the LHC with
the future luminosity of 300 and 3000 fb.Comment: 12 pages, 9 figures, 3 tables. Discussion with the relation of the
considered operators with the ones of the Warsaw basis extended. Missing
contribution to the gluon fusion amplitude added. Main results unchange
Low-scale neutrino seesaw mechanism and scalar dark matter
We discuss how two birds—the little hierarchy problem of low-scale type-I seesaw models and the search for a viable dark matter candidate—are (proverbially) killed by one stone: a new inert scalar state
The littlest Higgs is a cruiserweight
We study the exact (one-loop) effective potential of the littlest Higgs model
and determine the dependence of physical quantities, such as the vacuum
expectation value v_W and mass m_h of the Higgs boson, on the fundamental
parameters of the Lagrangian--masses, couplings of new states, the fundamental
scale f of the sigma model, and the coefficients of operators quadratically
sensitive to the cutoff of the theory. On the one hand, we show that it is
possible to have the electroweak ground state and a relatively large cutoff
\Lambda = 4\pi f with f in the 2 TeV range without requiring unnaturally small
coefficients for quadratically divergent quantities, and with only moderate
cancellations between the contribution of different sectors to the effective
potential of the Higgs. On the other hand, this cannot be achieved while at the
same time keeping m_h close to its (bantamweight) current lower bound of 114.4
GeV. The natural expectation for m_h is O(f), mainly because of large
logarithmically divergent contributions to the effective potential of the
top-quark sector. Even a fine-tuning at the level of O(10^{-2}) in the
coefficients of the quadratic divergences is not enough to produce small
physical Higgs masses, and the natural expectation is in the 800 GeV range
(cruiserweight) for f \sim 2 TeV. We conclude that the littlest Higgs model is
a solution of the little hierarchy problem, in the sense that it stabilizes the
electroweak symmetry breaking scale to be a factor of 100 less than the cutoff
of the theory, but this requires a quite large physical mass for the Higgs, and
hence precision electroweak studies should be redone accordingly. We also study
finite temperature corrections.Comment: 18 pages, 9 figures, RevTex4. Final version accepted for publication
in Phys. Rev.
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