1,513 research outputs found
Gauge bosons in a five-dimensional theory with localized gravity
We consider the possibility of gauge bosons living in the recently proposed
five-dimensional theory with localized gravity. We study the mass spectrum of
the Kaluza-Klein (KK) excitations of the gauge fields and calculate their
couplings to the boundaries of the fifth dimension. We find a different
behaviour from the case of the graviton. In particular, we find that the
massless mode is not localized in the extra dimension and that the KK
excitations have sizeable couplings to the two boundaries. We also discuss
possible phenomenological implications for the case of the standard model gauge
bosons.Comment: 10 pages, Late
Top Quark Compositeness: Feasibility and Implications
In models of electroweak symmetry breaking in which the SM fermions get their
masses by mixing with composite states, it is natural to expect the top quark
to show properties of compositeness. We study the phenomenological viability of
having a mostly composite top. The strongest constraints are shown to mainly
come from one-loop contributions to the T-parameter. Nevertheless, the presence
of light custodial partners weakens these bounds, allowing in certain cases for
a high degree of top compositeness. We find regions in the parameter space in
which the T-parameter receives moderate positive contributions, favoring the
electroweak fit of this type of models. We also study the implications of
having a composite top at the LHC, focusing on the process pp-> t\bar t t\bar t
(b\bar b) whose cross-section is enhanced at high-energies.Comment: 26 pages, 11 figure
Flavor hierarchies from dynamical scales
One main obstacle for any beyond the SM (BSM) scenario solving the hierarchy
problem is its potentially large contributions to electric dipole moments. An
elegant way to avoid this problem is to have the light SM fermions couple to
the BSM sector only through bilinears, . This possibility can be
neatly implemented in composite Higgs models. We study the implications of
dynamically generating the fermion Yukawa couplings at different scales,
relating larger scales to lighter SM fermions. We show that all flavor and
CP-violating constraints can be easily accommodated for a BSM scale of few TeV,
without requiring any extra symmetry. Contributions to B physics are mainly
mediated by the top, giving a predictive pattern of deviations in
and flavor observables that could be seen in future experiments.Comment: 25 pages, 5 figures; v2: corrections in some estimate
Towards the Ultimate SM Fit to Close in on Higgs Physics
With the discovery of the Higgs at the LHC, experiments have finally
addressed all aspects of the Standard Model (SM). At this stage, it is
important to understand which windows for beyond the SM (BSM) physics are still
open, and which are instead tightly closed. We address this question by
parametrizing BSM effects with dimension-six operators and performing a global
fit to the SM. We separate operators into different groups constrained at
different levels, and provide independent bounds on their Wilson coefficients
taking into account only the relevant experiments. Our analysis allows to
assert in a model-independent way where BSM effects can appear in Higgs
physics. In particular, we show that deviations from the SM in the differential
distributions of h->Vff are related to other observables, such as triple
gauge-boson couplings, and are then already constrained by present data. On the
contrary, BR(h-> Z+gamma) can still hide large deviations from the SM.Comment: 20 pages, 5 figures, v2: typos corrected. JHEP versio
The Composite Higgs and Light Resonance Connection
Weinberg sum-rules have been used in the past to successfully predict the
electromagnetic contribution to the charged-pion mass as a function of the
meson masses. Following the same approach we calculate in the minimal composite
Higgs model (MCHM) the Higgs mass as a function of the fermionic resonance
masses. The simplicity of the method allows us to study several versions of the
MCHM and show that a Higgs with a mass around 125 GeV requires, quite
generically, fermionic resonances below the TeV, and therefore accessible at
the LHC. We also examine the couplings of the Higgs to the SM fermions and
calculate their deviation from the SM value.Comment: Version to be published in JHE
Baryon Physics in Holographic QCD
In a simple holographic model for QCD in which the Chern-Simons term is
incorporated to take into account the QCD chiral anomaly, we show that baryons
arise as stable solitons which are the 5D analogs of 4D skyrmions. Contrary to
4D skyrmions and previously considered holographic scenarios, these solitons
have sizes larger than the inverse cut-off of the model, and therefore they are
predictable within our effective field theory approach. We perform a numerical
determination of several static properties of the nucleons and find a
satisfactory agreement with data. We also calculate the amplitudes of
``anomalous'' processes induced by the Chern-Simons term in the meson sector,
such as omega -> pi gamma and omega -> 3pi. A combined fit to baryonic and
mesonic observables leads to an agreement with experiments within 16%.Comment: 18 pages, version to appear in Nucl. Phys.
Baryon physics in a five-dimensional model of hadrons
We review the procedure to calculate baryonic properties using a recently
proposed five-dimensional approach to QCD. We show that this method give
predictions to baryon observables that agree reasonable well with the
experimental data.Comment: Contribution to "The Multi-facet of Skyrmions" edited by G. Brown and
M. Rho for World Scientific Publishing Co, 30
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