2,805 research outputs found
Two Higgs Bosons at the Tevatron and the LHC?
The best fit to the Tevatron results in the bb channel and the mild excesses
at CMS in the gamma-gamma channel at 136 GeV and in the tau-tau channel above
132 GeV can be explained by a second Higgs state in this mass range, in
addition to the one at 125 GeV recently discovered at the LHC. We show that a
scenario with two Higgs bosons at 125 GeV and 136 GeV can be consistent with
practically all available signal rates, including a reduced rate in the tau-tau
channel around 125 GeV as reported by CMS. An example in the parameter space of
the general NMSSM is given where, moreover, the signal rates of the 125 GeV
Higgs boson in the gamma-gamma channels are enhanced relative to the
expectation for a SM Higgs boson of this mass.Comment: 13 pages, 4 Table
Bosonic Quartic Couplings at LEP2
We list the set of C and P conserving anomalous quartic vector bosons
self-couplings which can be tested at LEP2 through triple vector boson
production. We show how this set can be embedded in manifestly SU(2)xU(1) gauge
invariant operators exhibiting an SU(2)_c global symmetry. We derive bounds on
these various couplings and show the most relevant distributions that can
enhance their contribution. We also find that an e+e- collider running at 500
GeV can improve the LEP2 limits by as much as three orders of magnitude.Comment: 21 pages, 7 figure
GRACE at ONE-LOOP: Automatic calculation of 1-loop diagrams in the electroweak theory with gauge parameter independence checks
We describe the main building blocks of a generic automated package for the
calculation of Feynman diagrams. These blocks include the generation and
creation of a model file, the graph generation, the symbolic calculation at an
intermediate level of the Dirac and tensor algebra, implementation of the loop
integrals, the generation of the matrix elements or helicity amplitudes,
methods for the phase space integrations and eventually the event generation.
The report focuses on the fully automated systems for the calculation of
physical processes based on the experience in developing GRACE-loop. As such, a
detailed description of the renormalisation procedure in the Standard Model is
given emphasizing the central role played by the non-linear gauge fixing
conditions for the construction of such automated codes. The need for such
gauges is better appreciated when it comes to devising efficient and powerful
algorithms for the reduction of the tensorial structures of the loop integrals.
A new technique for these reduction algorithms is described. Explicit formulae
for all two-point functions in a generalised non-linear gauge are given,
together with the complete set of counterterms. We also show how infrared
divergences are dealt with in the system. We give a comprehensive presentation
of some systematic test-runs which have been performed at the one-loop level
for a wide variety of two-to-two processes to show the validity of the gauge
check. These cover fermion-fermion scattering, gauge boson scattering into
fermions, gauge bosons and Higgs bosons scattering processes. Comparisons with
existing results on some one-loop computation in the Standard Model show
excellent agreement. We also briefly recount some recent development concerning
the calculation of mutli-leg one-loop corrections.Comment: 131 pages. Manuscript expanded quite substantially with the inclusion
of an overview of automatic systems for the calculation of Feynman diagrams
both at tree-level and one-loop. Other additions include issues of
regularisation, width effects and renormalisation with unstable particles and
reduction of 5- and 6-point functions. This is a preprint version, final
version to appear as a Phys. Re
Magnetic Properties of the Metamagnet Ising Model in a three-dimensional Lattice in a Random and Uniform Field
By employing the Monte Carlo technique we study the behavior of Metamagnet
Ising Model in a random field. The phase diagram is obtained by using the
algorithm of Glaubr in a cubic lattice of linear size with values ranging
from 16 to 42 and with periodic boundary conditions.Comment: 4 pages, 6 figure
Relic density of neutralino dark matter in the MSSM with CP violation
We calculate the relic density of dark matter in the MSSM with CP violation.
We analyse various scenarios of neutralino annihilation: the cases of a bino,
bino-wino and bino-Higgsino LSP, annihilation through Higgs, as well as
sfermion coannihilation scenarios. Large phase effects are found, on the one
hand due to shifts in the masses, on the other hand due to modifications of the
couplings. Taking special care to disentangle the effects in masses and
couplings, we demonstrate that the presence of CP phases can have a significant
influence on the neutralino relic abundance. Typical variations in \Omega h^2
solely from modifications in the couplings are O(10%-100%), but can reach an
order of magnitude in some cases.Comment: 36 pages, 21 figures (low resolution). A version with high-resolution
figures can be downloaded from http://cern.ch/kraml/papers/omc
Summary of the 13th IACHEC Meeting
We summarize the outcome of the 13th meeting of the International
Astronomical Consortium for High Energy Calibration (IACHEC), held at Tenuta
dei Ciclamini (Avigliano Umbro, Italy) in April 2018. Fifty-one scientists
directly involved in the calibration of operational and future high-energy
missions gathered during 3.5 days to discuss the current status of the X-ray
payload inter-calibration and possible approaches to improve it. This summary
consists of reports from the various working groups with topics ranging from
the identification and characterization of standard calibration sources,
multi-observatory cross-calibration campaigns, appropriate and new statistical
techniques, calibration of instruments and characterization of background, and
communication and preservation of knowledge and results for the benefit of the
astronomical community.Comment: 12 page
A new look at the cosmic ray positron fraction
The positron fraction in cosmic rays was found to be a steadily increasing in
function of energy, above 10 GeV. This behaviour contradicts standard
astrophysical mechanisms, in which positrons are secondary particles, produced
in the interactions of primary cosmic rays during the propagation in the
interstellar medium. The observed anomaly in the positron fraction triggered a
lot of excitement, as it could be interpreted as an indirect signature of the
presence of dark matter species in the Galaxy. Alternatively, it could be
produced by nearby astrophysical sources, such as pulsars. Both hypotheses are
probed in this work in light of the latest AMS-02 positron fraction
measurements. The transport of the primary and secondary positrons in the
Galaxy is described using a semi-analytic two-zone model. MicrOMEGAs is used to
model the positron flux generated by dark matter species. The description of
the positron fraction from astrophysical sources is based on the pulsar
observations included in the ATNF catalogue. We find that the mass of the
favoured dark matter candidates is always larger than 500 GeV. The only dark
matter species that fulfils the numerous gamma ray and cosmic microwave
background bounds is a particle annihilating into four leptons through a light
scalar or vector mediator, with a mixture of tau (75%) and electron (25%)
channels, and a mass between 0.5 and 1 TeV. The positron anomaly can also be
explained by a single astrophysical source and a list of five pulsars from the
ATNF catalogue is given. Those results are obtained with the cosmic ray
transport parameters that best fit the B/C ratio. Uncertainties in the
propagation parameters turn out to be very significant. In the WIMP
annihilation cross section to mass plane for instance, they overshadow the
error contours derived from the positron data.Comment: 20 pages, 16 figures, accepted for publication in A&A, corresponds to
published versio
Glassy transition in the three-dimensional random field Ising model
The high temperature phase of the three dimensional random field Ising model
is studied using replica symmetry breaking framework. It is found that, above
the ferromagnetic transition temperature T_f, there appears a glassy phase at
intermediate temperatures T_f<T<T_b while the usual paramagnetic phase exists
for T>T_b only. Correlation length at T_b is computed and found to be
compatible with previous numerical results.Comment: 7 pages, LaTeX file, preprint 1014 - Rome
Local Structure of La1-xSrxCoO3 determined from EXAFS and neutron PDF studies
The combined local structure techniques, extended x-ray absorption fine
structure (EXAFS) and neutron pair distribution function analysis, have been
used for temperatures 4 <= T <= 330 K to rule out a large Jahn-Teller (JT)
distortion of the Co-O bond in La1-xSrxCoO3 for a significant fraction of Co
sites (x <= 0.35), indicating few, if any, JT-active, singly occupied e_g Co
sites exist.Comment: 5 page
Letting the Right Ones In: Whitelists, Jurisdictional Reputation, and the Racial Dynamics of Online Gambling Regulation.
Using a case study of a recent UK whitelist intended to regulate online gambling, I examine the affective politics of listing. I pay particular attention to the racial dynamics of black and white listing. By charting how the gambling whitelist worked and failed to work as a tool in the designation of jurisdictional reputation, I argue that the use and subsequent abandonment of the whitelist shows the centrality of racial dynamics to listing practices, particularly in relation to how the list was deployed in debates about the trustworthiness of the Kahnawá:ke territory and Antigua and Barbuda. In section 5 I examine what happened after the demise of the online gambling whitelist. Although non-listing techniques of governance look to be expanding, in the form of increased surveillance of individual gamblers, lists continue to play a key role in the UK government’s new model of gambling regulation. I suggest that this confirms the co-constitutive and mutually reinforcing nature of black and white lists as techniques of governance, and the value of exploring them and their racialized implications together
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