172 research outputs found
Quantum evolution of scalar fields in Robertson-Walker space-time
We study the field theory in a flat Robertson-Walker
space-time using the functional Sch\"odinger picture. We introduce a simple
Gaussian approximation to analyze the time evolution of pure states and we
establish the renormalizability of the approximation. We also show that the
energy-momentum tensor in this approximation is finite once we consider the
usual mass and coupling constant renormalizations.Comment: Revtex file, 19 pages, no figures. Compressed ps version available at
http://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-912.ps.Z or at
ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-912.ps.
Signals of Two Universal Extra Dimensions at the LHC
Extensions of the standard model with universal extra dimensions are
interesting both as phenomenological templates as well as model-building
fertile ground. For instance, they are one the prototypes for theories
exhibiting compressed spectra, leading to difficult searches at the LHC since
the decay products of new states are soft and immersed in a large standard
model background. Here we study the phenomenology at the LHC of theories with
two universal extra dimensions. We obtain the current bound by using the
production of second level excitations of electroweak gauge bosons decaying to
a pair of leptons and study the reach of the LHC Run~II in this channel. We
also introduce a new channel originating in higher dimensional operators and
resulting in the single production of a second level quark excitation. Its
subsequent decay into a hard jet and lepton pair resonance would allow the
identification of a more model-specific process, unlike the more generic vector
resonance signal. We show that the sensitivity of this channel to the
compactification scale is very similar to the one obtained using the vector
resonance.Comment: 11 pages and 6 figure
Present Bounds on New Neutral Vector Resonances from Electroweak Gauge Boson Pair Production at the LHC
Several extensions of the Standard Model predict the existence of new neutral
spin-1 resonances associated to the electroweak symmetry breaking sector. Using
the data from ATLAS (with integrated luminosity of L=1.02 fb^{-1}) and CMS
(with integrated luminosity of L=1.55 fb^{-1}) on the production of W+W- pairs
through the process pp -> l^+ l^{\prime -} \sla{E}_T, we place model
independent bounds on these new vector resonances masses, couplings and widths.
Our analyses show that the present data excludes new neutral vector resonances
with masses up to 1-2.3 TeV depending on their couplings and widths. We also
demonstrate how to extend our analysis framework to different models working a
specific example.Comment: 10 pages, 6 figure
Bounds on Scalar Leptoquarks from Z Physics
We analyse the constraints on scalar leptoquarks coming from radiative
corrections to physics. We perform a global fitting to the LEP data
including the contributions of the most general effective Lagrangian for scalar
leptoquarks, which exhibits the gauge invariance. We
show that the bounds on leptoquarks that couple to the top quark are much
stronger than the ones obtained from low energy experiments.Comment: RevTeX 3.0, 26 pages, 4 postscript figures included as uufil
Constraining anomalous Higgs interactions
The recently announced Higgs discovery marks the dawn of the direct probing
of the electroweak symmetry breaking sector. Sorting out the dynamics
responsible for electroweak symmetry breaking now requires probing the Higgs
interactions and searching for additional states connected to this sector. In
this work we analyze the constraints on Higgs couplings to the standard model
gauge bosons using the available data from Tevatron and LHC. We work in a
model--independent framework expressing the departure of the Higgs couplings to
gauge bosons by dimension--six operators. This allows for independent
modifications of its couplings to gluons, photons and weak gauge bosons while
still preserving the Standard Model (SM) gauge invariance. Our results indicate
that best overall agreement with data is obtained if the cross section of Higgs
production via gluon fusion is suppressed with respect to its SM value and the
Higgs branching ratio into two photons is enhanced, while keeping the
production and decays associated to couplings to weak gauge bosons close to
their SM prediction.Comment: v3: Added acknowledgment to FP7 ITN INVISIBLES (Marie Curie Actions
PITN-GA-2011-289442). Nothing else changed with respect to v
Signals for New Spin-1 Resonances in Electroweak Gauge Boson Pair Production at the LHC
The mechanism of electroweak symmetry breaking (EWSB) will be directly
scrutinized soon at the CERN Large Hadron Collider (LHC). We analyze the LHC
potential to look for new vector bosons associated with the EWSB sector. We
present a possible model independent approach to search for these new spin--1
resonances. We show that the analyses of the processes pp --> l^+ l^- Emiss_T,
l^\pm j j Emiss_T, l^\pm l^+ l^- Emiss_T, and l^+ l^- j j (with l=e or \mu and
j=jet) have a large reach at the LHC and can lead to the discovery or exclusion
of many EWSB scenarios such as Higgsless models.Comment: 10 pages, 11 figure
Finding the Higgs Boson through Supersymmetry
The study of displaced vertices containing two b--jets may provide a double
discovery at the Large Hadron Collider (LHC): we show how it may not only
reveal evidence for supersymmetry, but also provide a way to uncover the Higgs
boson necessary in the formulation of the electroweak theory in a large region
of the parameter space. We quantify this explicitly using the simplest minimal
supergravity model with bilinear breaking of R-parity, which accounts for the
observed pattern of neutrino masses and mixings seen in neutrino oscillation
experiments.Comment: 7 pages, 7 figures. Final version to appear at PRD. Discussion and
results were enlarge
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