1,153 research outputs found
A Twisted Custodial Symmetry in the Two-Higgs-Doublet Model
In the Standard Model for electroweak interactions, the Higgs sector is known
to display a "custodial" symmetry protecting the mass relation
m_{W^\pm}^2=m_{W_3}^2 from large corrections. When considering extensions of
the scalar sector, this symmetry has to be introduced by hand in order to pass
current electroweak precision tests in a natural way. In this Letter we
implement a generalized custodial symmetry in the two-Higgs-doublet model.
Assuming the invariance of the potential under CP transformations, we prove the
existence of a new custodial scenario characterized by m_{H^\pm}^2=m_{H^0}^2
instead of m_{H^\pm}^2=m_{A^0}^2. Consequently the pseudoscalar A^0 may be much
lighter than the charged H^\pm, giving rise to interesting phenomenology.Comment: 4 pages, RevTeX
Global geometry of the 2+1 rotating black hole
The generic rotating BTZ black hole, obtained by identifications in AdS3
space through a discrete subgroup of its isometry group, is investigated within
a Lie theoretical context. This space is found to admit a foliation by
two-dimensional leaves, orbits of a two-parameter subgroup of SL(2,R) and
invariant under the BTZ identification subgroup. A global expression for the
metric is derived, allowing a better understanding of the causal structure of
the black hole.Comment: 9 pages, 1 figur
Sphaleron-Bisphaleron bifurcations in a custodial-symmetric two-doublets model
The standard electroweak model is extended by means of a second
Brout-Englert-Higgs-doublet. The symmetry breaking potential is chosen is such
a way that (i) the Lagrangian possesses a custodial symmetry, (ii) a static,
spherically symmetric ansatz of the bosonic fields consistently reduces the
Euler-Lagrange equations to a set of differential equations. The potential
involves, in particular, products of fields of the two doublets, with a
coupling constant .Static, finite energy solutions of the classical
equations are constructed. The regular, non-trivial solutions having the lowest
classical energy can be of two types: sphaleron or bisphaleron, according to
the coupling constants. A special emphasis is put to the bifurcation between
these two types of solutions which is analyzed in function of the different
constants of the model,namely of .Comment: 10 pages, 3 figure
New Developments in MadGraph/MadEvent
We here present some recent developments of MadGraph/MadEvent since the
latest published version, 4.0. These developments include: Jet matching with
Pythia parton showers for both Standard Model and Beyond the Standard Model
processes, decay chain functionality, decay width calculation and decay
simulation, process generation for the Grid, a package for calculation of
quarkonium amplitudes, calculation of Matrix Element weights for experimental
events, automatic dipole subtraction for next-to-leading order calculations,
and an interface to FeynRules, a package for automatic calculation of Feynman
rules and model files from the Lagrangian of any New Physics model.Comment: 6 pages, 3 figures. Plenary talk given at SUSY08, Seoul, South Korea,
June 2008. To appear in the proceeding
Single top production in a non-minimal supersymmetric model
We study single top production at the LHC in a SUSY-QCD model with a heavy
Dirac gluino. The presence of a heavy Dirac gluino allows for notable top-up
flavour changing neutral currents. In this scenario, we find that the process
ug->tg gives the largest contribution to single top production via FCNCs at the
LHC. The key features of this signal are that the top quark is produced very
forward and that it is asymmetric to its anti-top counterpart, as the latter
lacks a valence quark.Comment: 9 pages, 4 figures, a background added, references added, minor
revisions, to be published in Phys. Lett.
A New Look at an Old Mass Relation
New data from neutrino oscillation experiments motivate us to extend a
successful mass relation for the charged leptons to the other fundamental
fermions. This new universal relation requires a Dirac mass around 3 10^-2 eV
for the lightest neutrino and rules out a maximal atmospheric mixing. It also
suggests a specific decomposition of the CKM mixing matrix.Comment: 8 pages, 2 figure
Maverick dark matter at colliders
Assuming that dark matter is a weakly interacting massive particle (WIMP)
species X produced in the early Universe as a cold thermal relic, we study the
collider signal of pp or ppbar -> XXbar + jets and its distinguishability from
standard-model background processes associated with jets and missing energy. We
assume that the WIMP is the sole particle related to dark matter within reach
of the LHC--a "maverick" particle--and that it couples to quarks through a
higher dimensional contact interaction. We simulate the WIMP final-state signal
XXbar + jet and dominant standard-model (SM) background processes and find that
the dark-matter production process results in higher energies for the colored
final state partons than do the standard-model background processes, resulting
in more QCD radiation and a higher jet multiplicity. As a consequence, the
detectable signature of maverick dark matter is an excess over standard-model
expectations of events consisting of large missing transverse energy, together
with large leading jet transverse momentum and scalar sum of the transverse
momenta of the jets. Existing Tevatron data and forthcoming LHC data can
constrain (or discover!) maverick dark matter.Comment: 11 pages, 7 figure
Is Vtb=1 ?
The strongest constraint on Vtb presently comes from the 3 x 3 unitarity of
the CKM matrix, which fixes Vtb to be very close to one. If the unitarity is
relaxed, current information from top production at Tevatron still leaves open
the possibility that Vtb is sizably smaller than one. In minimal extensions of
the standard model with extra heavy quarks, the unitarity constraints are much
weaker and the EW precision parameters entail the strongest bounds on Vtb. We
discuss the experimental perspectives of discovering and identifying such new
physics models at the Tevatron and the LHC, through a precise measurement of
Vtb from the single top cross sections and by the study of processes where the
extra heavy quarks are produced.Comment: 19 pages, 8 figure
Detecting a stochastic gravitational wave background with the Laser Interferometer Space Antenna
The random superposition of many weak sources will produce a stochastic
background of gravitational waves that may dominate the response of the LISA
(Laser Interferometer Space Antenna) gravitational wave observatory. Unless
something can be done to distinguish between a stochastic background and
detector noise, the two will combine to form an effective noise floor for the
detector. Two methods have been proposed to solve this problem. The first is to
cross-correlate the output of two independent interferometers. The second is an
ingenious scheme for monitoring the instrument noise by operating LISA as a
Sagnac interferometer. Here we derive the optimal orbital alignment for
cross-correlating a pair of LISA detectors, and provide the first analytic
derivation of the Sagnac sensitivity curve.Comment: 9 pages, 11 figures. Significant changes to the noise estimate
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