19,235 research outputs found
Multilepton production via top flavour-changing neutral couplings at the CERN LHC
Zt and gamma t production with Z -> l+ l- and t -> Wb -> l nu b provides the
best determination of top flavour-changing neutral couplings at the LHC. The
bounds on tc couplings eventually derived from these processes are similar to
those expected from top decays, while the limits on tu couplings are better by
a factor of two. The other significant Z and W decay modes are also
investigated.Comment: 30 pages, 23 PS figures. Uses epsfig.sty and elsart.sty. Added some
references and corrected some typos. Added more comments about statistics.
Using elsart.sty reduces the size to 30 pages. Published in Nucl. Phys.
Multiphoton signals of a (96 GeV?) stealth boson
Cascade decays of new scalars into final states with multiple photons and
possibly quarks may lead to distinctive experimental signatures at high-energy
colliders. Such signals are even more striking if the scalars are highly
boosted, as when produced from the decay of a much heavier resonance. We study
this type of events within the framework of the minimal stealth boson model, an
anomaly-free extension of the Standard Model with two
complex scalar singlets. It is shown that, while those signals may have cross
sections that might render them observable with LHC Run 2 data, they have
little experimental coverage. We also establish a connection with a CMS excess
observed in searches for new scalars decaying into diphoton final states near
96 GeV. In particular, we conclude that the predicted multiphoton signatures
are compatible with such excess.Comment: LaTeX 32 pages. Comments added and discussions extended. Final
version in EPJ
A closer look at the possible CMS signal of a new gauge boson
The CMS collaboration has recently reported a 2.8 excess of
events with an invariant mass around 2 TeV. This observation can be explained
in the context of standard model extensions with new gauge bosons ,
and heavy neutrinos coupling (mainly) to the electron. We discuss additional
signals that allow to confirm or discard the and hypotheses.Comment: ReVTeX 5 page
Constraints on the Wtb vertex from early LHC data
We use the recent measurements of top quark decay asymmetries in ATLAS and
the t-channel single top cross section in CMS to set the first combined LHC
limits on the Wtb vertex. This combination allows to obtain much better limits
than the separate measurements. The resulting constraints are comparable,
although still weaker, than the ones obtained using Tevatron data with much
more statistics.Comment: RevTeX 4 page
A new method to find the potential center of N-body systems
We present a new and fast method to nd the potential center of an N-body
distribution. The method uses an iterative algorithm which exploits the fact that
the gradient of the potential is null at its center: it uses a smoothing radius to
avoid getting trapped in secondary minima. We have tested this method on several
random realizations of King models (in which the numerical computation of this
center is rather dicult, due to the constant density within their cores), and com-
pared its performance and accuracy against a more straightforward, but computer
intensive method, based on cartesian meshes of increasing spatial resolution. In all
cases, both methods converged to the same center, within the mesh resolution, but
the new method is two orders of magnitude faster.
We have also tested the method with one astronomical problem: the evolu-
tion of a 105 particle King model orbiting around a xed potential that represents
our Galaxy. We used a spherical harmonics expansion N-body code, in which the
potential center determination is crucial for the correct force computation. We
compared this simulation with another one in which a method previously used to
determine the expansion center is employed (White 1983). Our routine gives better
results in energy conservation and mass loss.Fil: Aguilar, L. A.. Universidad Nacional Autonoma de Mexico. Instituto de Astronomia; MéxicoFil: Cruz, F.. Universidad Nacional Autonoma de Mexico. Instituto de Astronomia; MéxicoFil: Carpintero, Daniel Diego. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentin
Shedding light on the asymmetry: the photon handle
We investigate a charge asymmetry in production at the LHC
that provides complementary information to the measured asymmetries in production. We estimate the experimental uncertainty in its measurement at
the LHC with 8 and 14 TeV. For new physics models that simultaneously reproduce
the asymmetry excess in at the Tevatron and the SM-like asymmetry at
the LHC, the measurement in at the LHC could exhibit
significant deviations with respect to the SM prediction.Comment: LaTeX 15 page
Charging Interacting Rotating Black Holes in Heterotic String Theory
We present a formulation of the stationary bosonic string sector of the whole
toroidally compactified effective field theory of the heterotic string as a
double Ernst system which, in the framework of General Relativity describes, in
particular, a pair of interacting spinning black holes; however, in the
framework of low--energy string theory the double Ernst system can be
particularly interpreted as the rotating field configuration of two interacting
sources of black hole type coupled to dilaton and Kalb--Ramond fields. We
clarify the rotating character of the --component of the
antisymmetric tensor field of Kalb--Ramond and discuss on its possible torsion
nature. We also recall the fact that the double Ernst system possesses a
discrete symmetry which is used to relate physically different string vacua.
Therefore we apply the normalized Harrison transformation (a charging symmetry
which acts on the target space of the low--energy heterotic string theory
preserving the asymptotics of the transformed fields and endowing them with
multiple electromagnetic charges) on a generic solution of the double Ernst
system and compute the generated field configurations for the 4D effective
field theory of the heterotic string. This transformation generates the
vector field content of the whole low--energy heterotic string
spectrum and gives rise to a pair of interacting rotating black holes endowed
with dilaton, Kalb--Ramond and multiple electromagnetic fields where the charge
vectors are orthogonal to each other.Comment: 15 pages in latex, revised versio
Top effective operators at the ILC
We investigate the effect of top trilinear operators in t tbar production at
the ILC. We find that the sensitivity to these operators largely surpasses the
one achievable by the LHC either in neutral or charged current processes,
allowing to probe new physics scales up to 4.5 TeV for a centre of mass energy
of 500 GeV. We show how the use of beam polarisation and an eventual energy
upgrade to 1 TeV allow to disentangle all effective operator contributions to
the Ztt and gamma tt vertices.Comment: LaTeX 13 pages. Typos corrected. Final version in JHE
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