538 research outputs found
The Unhiggs
We examine a scenario where the Higgs is part of an approximate conformal
field theory, and has a scaling dimension greater than one. Such an unparticle
Higgs (or Unhiggs) can still break electroweak symmetry and unitarize WW
scattering, but its gauge couplings are suppressed. An Unhiggs model has a
reduced sensitivity of the weak scale to the cutoff, and can thus provide a
solution to the little hierarchy problem.Comment: 21 pages, 9 figures; v2: further discussion, references added,
version published in JHE
Model Independent Framework for Searches of Top Partners
We propose a model-independent and general framework to study the LHC
phenomenology of top partners, i.e. Vector-Like quarks including particles with
different electro-magnetic charge. We consider Vector-Like quarks embedded in
general representations of the weak SU(2)L, coupling to all Standard Model
quarks via Yukawa mixing focusing on the case of a single multiplet. We show
that, with very minimal and quite general assumptions, top partners may be
studied in terms of few parameters in an effective Lagrangian description with
a clear and simple connection with experimental observables. We also
demonstrate that the parametrisation can be applied as well to cases with many
Vector-like multiplets, thus covering most realistic models of New Physics. We
perform a numerical study to understand the conclusions which can be drawn
within such a description and the expected potential for discovery or exclusion
at the LHC. Our main results are a clear connection between branching ratios
and single production channels, and the identification of novel interesting
channels to be studied at the LHC.Comment: 42 pages, 2 figures, 20 tables, added an appendix with a discussion
of coupling chirality in general scenarios; added a comparison of collider
and flavour bounds; added details about the range of validity of the
framework. References adde
Electroweak Precision Observables and the Unhiggs
We compute one-loop corrections to the S and T parameters in the Unhiggs
scenario. In that scenario, the Standard Model Higgs is replaced by a non-local
object, called the Unhiggs, whose spectral function displays a continuum above
the mass gap. The Unhiggs propagator has effectively the same UV properties as
the Standard Model Higgs propagator, which implies that loop corrections to the
electroweak precision observables are finite and calculable. We show that the
Unhiggs is consistent with electroweak precision tests when its mass gap is at
the weak scale; in fact, it then mimics a light SM Higgs boson. We also argue
that the Unhiggs, while being perfectly visible to electroweak precision
observables, is invisible to detection at LEP.Comment: 13 pages; v2: references added, discussion of production
cross-section expande
The Minimal Set of Electroweak Precision Parameters
We present a simple method for analyzing the impact of precision electroweak
data above and below the Z-peak on flavour-conserving heavy new physics. We
find that experiments have probed about ten combinations of new physics
effects, which to a good approximation can be condensed into the effective
oblique parameters Shat, That, Uhat, V, X, W, Y (we prove positivity
constraints W, Y >= 0) and three combinations of quark couplings (including a
distinct parameter for the bottom). We apply our method to generic extra Z'
vectors.Comment: 22 pages, 3 figure
The AdS/CFT/Unparticle Correspondence
We examine the correspondence between the anti-de Sitter (AdS) description of
conformal field theories (CFTs) and the unparticle description of CFTs. We show
how unparticle actions are equivalent to holographic boundary actions for
fields in AdS, and how massive unparticles provide a new type of infrared
cutoff that can be simply implemented in AdS by a soft breaking of conformal
symmetry. We also show that processes involving scalar unparticles with
dimensions d_s<2 or fermion unparticles with dimensions d_f<5/2 are insensitive
to ultraviolet cutoff effects. Finally we show that gauge interactions for
unparticles can be described by bulk gauge interactions in AdS and that they
correspond to minimal gauging of the non-local effective action, and we compute
the fermion unparticle production cross-section.Comment: 26 pages, 1 figur
H â γγ beyond the Standard Model
We consider the H â γγ decay process and the gluon fusion production of a light Higgs, and provide a general framework for testing models of new physics beyond the Standard Model. We apply our parametrisation to typical
models extending the Standard Model in 4 and 5 dimensions, and show how the parametrisation can be used to discriminate between different scenarios of new physics at the Large Hadron Collider and at future Linear Colliders
Sifting composite from elementary models at FCCee and CePC
New Physics models with either an elementary or composite origin are often
associated with a similar imprint in a direct search at colliders, case in
point being the production of a light pseudoscalar in association with a
monochromatic photon from the decay of a Z boson at future colliders. We
exploit the correlation between the discovery of a signal in the Z decays and
electroweak precision measurements as a tool to distinguish a composite model
from an elementary scalar one. Our results offer an appealing and rich physics
case for future colliders and demonstrate how a lepton collider at the Z mass
can be a discovery machine for new physics in the Higgs sector.Comment: 7 Pages, 2 Figure
Bosonic Seesaw in the Unparticle Physics
Recently, conceptually new physics beyond the Standard Model has been
proposed by Georgi, where a new physics sector becomes conformal and provides
"unparticle" which couples to the Standard Model sector through higher
dimensional operators in low energy effective theory. Among several
possibilities, we focus on operators involving the (scalar) unparticle, Higgs
and the gauge bosons. Once the Higgs develops the vacuum expectation value
(VEV), the conformal symmetry is broken and as a result, the mixing between the
unparticle and the Higgs boson emerges. In this paper, we consider a natural
realization of bosonic seesaw in the context of unparticle physics. In this
framework, the negative mass squared or the electroweak symmetry breaking
vacuum is achieved as a result of mass matrix diagonalization. In the
diagonalization process, it is important to have zero value in the
(1,1)-element of the mass matrix. In fact, the conformal invariance in the
hidden sector can actually assure the zero of that element. So, the bosonic
seesaw mechanism for the electroweak symmetry breaking can naturally be
understood in the framework of unparticle physics.Comment: 5 pages, no figure; added one more referenc
Superluminal neutrinos in long baseline experiments and SN1987a
Precise tests of Lorentz invariance in neutrinos can be performed using long
baseline experiments such as MINOS and OPERA or neutrinos from astrophysical
sources. The MINOS collaboration reported a measurement of the muonic neutrino
velocities that hints to super-luminal propagation, very recently confirmed at
6 sigma by OPERA. We consider a general parametrisation which goes beyond the
usual linear or quadratic violation considered in quantum-gravitational models.
We also propose a toy model showing why Lorentz violation can be specific to
the neutrino sector and give rise to a generic energy behaviour E^alpha, where
alpha is not necessarily an integer number. Supernova bounds and the preferred
MINOS and OPERA regions show a tension, due to the absence of shape distortion
in the neutrino bunch in the far detector of MINOS. The energy independence of
the effect has also been pointed out by the OPERA results.Comment: 22 pages, 7 figures; comment on Cherenkov emission added, version
matching JHEP published pape
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