230 research outputs found

### Signatures of Non-Standard Electroweak Symmetry Breaking

This is the write-up of a talk given at the EW session in Moriond (March
2012). I summarize some non-standard electroweak scenarios, and how they
predict the existence of new spin-two resonances. Spin-two resonances, whether
coming from the compactification of extra-dimensions or from a new sector of
strong interactions, exhibit the same interactions with the Standard Model.
This is a consequence of Lorentz and CP invariance, which we assume would be
preserved by the new strong sector. Although this would seem to support the
holographic duality between strongly interacting theories in four-dimensions
and extra-dimensional theories, I show that there is a way to distinguish
between the two sides of the "duality", which constitutes an explicit example
of its breakdown

### (Not) Summing over Kaluza-Kleins

Models in extra-dimensions have unique features. Many of their surprising
properties simply result from the underlying 5D structure. This structure shows
up as ``Sum Rules'' involving the whole tower of Kaluza-Kleins. In this paper,
we present a holographic shortcut and derive these results without solving the
eigenvalue problem: we express 4D physical quantities directly in terms of the
5D metric. In warped space, one can go further and isolate the effect of the
new physics sector. This method can be used for any 5D model, and we apply it
here to the case of holographic QCD and technicolor

### Non standard neutrino interactions at LEP2 and the LHC

We consider Non-Standard neutrino Interactions (NSI) connecting two neutrinos
with two first-generation fermions ($e, u$ or $d$), which we assume to arise at
at dimension eight due to New Physics. The coefficient is normalised as $4
\epsilon G_F/\sqrt{2}$. We explore signatures of NSI-on-electrons at LEP2, and
of NSI-on-quarks at the LHC, treating the NSI as contact interactions at both
energies. In models where the coefficients of dangerous dimension six operators
are suppressed by cancellations, LEP2 provides interesting bounds on NSI
operators (\epsilon \lsim 10^{-2} - 10^{-3}), which arise because $\sqrt{s}
\sim 200$ GeV, and the cancellation applied at zero momentum transfer. At the
LHC, we use the Equivalence Theorem, which relates the longitudinal $W$ to the
Higgs, to estimate the rate for $\bar{q} q W^+W^- e_\alpha^+ e_\beta^-$ induced
by NSI. We find that the cross-section is small, but that the outgoing
particles have very high $p_T > 400$ GeV, which reduces the issue of
backgrounds. In a conservative scenario, we find that the LHC at 14 TeV and
with 100 fb$^{-1}$ of data would have a sensitivity to \epsilon \gsim 3 \times
10^{-3}.Comment: 4 pages, contribution to NUFACT 11, XIIIth International Workshop on
Neutrino Factories, Super beams and Beta beams, 1-6 August 2011, CERN and
University of Geneva (Submitted to IOP conference series

### Prima Facie Evidence against Spin-Two Higgs Impostors

The new particle X recently discovered by the ATLAS and CMS Collaborations is
widely expected to have spin zero, but this remains to be determined. The
leading alternative is that X has spin two, presumably with graviton-like
couplings. We show that measurements of the X particle to pairs of vector
bosons constrain such scenarios. In particular, a graviton-like Higgs impostor
in scenarios with a warped extra dimension of AdS type is prima facie excluded,
principally because they predict too small a ratio between the X couplings to
WW and ZZ, compared with that to photons. The data also disfavour universal
couplings to pairs of photons and gluons, which would be predicted in a large
class of graviton-like models.Comment: 17 pages, 3 figure

### Associated Production Evidence against Higgs Impostors and Anomalous Couplings

There is still no proof that the new particle $X$ recently discovered by the
ATLAS and CMS Collaborations indeed has spin zero and positive parity, as
confidently expected. We show here that the energy dependence of associated
$W/Z + X$ production would be much less for a $J^P = 0^+$ boson with minimal
couplings, such as the Higgs boson of the Standard Model, than for a spin-two
particle with graviton-like couplings or a spin-zero boson with non-minimal
couplings. The $W/Z + (X \to {\bar b}b)$ signal apparently observed by the CDF
and D0 Collaborations can be used to predict the cross section for the same
signal at the LHC that should be measured under the spin-two and different
spin-zero hypotheses. The spin-two prediction exceeds by an order of magnitude
the upper limits established by the ATLAS and CMS Collaborations, which are
consistent with the minimal $0^+$ prediction, thereby providing {\it secunda
facie} evidence against spin-two Higgs impostors. Similar analyses of energy
dependences provide evidence against $0^-$ impostors, non-minimal scalar boson
couplings, including the best LHC limits on dimension-six operators. Comparing
the LHC vector boson fusion cross sections at 7 and 8 TeV in the centre of mass
provides additional but weaker evidence in favour of the identification of the
$X$ particle as a $J^P = 0^+$ boson with minimal couplings.Comment: 15 pages, 7 figure

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