1,593 research outputs found
Impact of semi-annihilations on dark matter phenomenology - an example of Z_N symmetric scalar dark matter
We study the impact of semi-annihilations x_i x_j x_k X, where x_i is any
dark matter and X is any standard model particle, on dark matter phenomenology.
We formulate minimal scalar dark matter models with an extra doublet and a
complex singlet that predict non-trivial dark matter phenomenology with
semi-annihilation processes for different discrete Abelian symmetries Z_N, N>2.
We implement two such example models with Z_3 and Z_4 symmetry in micrOMEGAs
and work out their phenomenology. We show that both semi-annihilations and
annihilations involving only particles from two different dark matter sectors
significantly modify the dark matter relic abundance in this type of models. We
also study the possibility of dark matter direct detection in XENON100 in those
models.Comment: 17 pages, 4 figure
Electroweak corrections to Higgs production through ZZ fusion at the linear collider
We present the full order alpha electroweak radiative corrections to e+e- ->
e+e-H. The computation is performed with the help of GRACE-loop. The extraction
of the full QED corrections is performed, these are quite large at threshold.
The genuine weak corrections, for the linear collider energies, when expressed
in the G_mu scheme are of order -2 to -4 for Higgs masses preferred by the
latest precision data. We also extract the m_t^2 type corrections and make a
comparison with the weak corrections for the process e+e- ->nu nu H.Comment: 16 pages and 6 figure
SUSY Higgs at the LHC: large stop mixing effects and associated production
We revisit the effect of the large stop mixing on the decay and production of the lightest SUSY Higgs at the LHC. We stress that whenever the inclusive 2-photon signature is substantially reduced, associated production, and , with the subsequent decay of the Higgs into photons is enhanced and becomes an even more important discovery channel. We also point out that these reductions in the inclusive channel do not occur for the smallest Higgs mass where the significance is known to be lowest. We show that in such scenarios the Higgs can be produced in the decay of the heaviest stop. For not too heavy masses of the pseudo-scalar Higgs where the inclusive channel is even further reduced, we show that large stop mixing also allows the production of the pseudo-scalar Higgs through stop decays. These large mixing scenarios therefore offer much better prospects than previously thought. As a by-product we have recalculated stop1-stop1-h production at the LHC and give a first evaluation of stop1-stop1-Z
Full order alpha electroweak corrections to double Higgs-strahlung at the linear collider
We present the full order alpha electroweak radiative corrections to the
double Higgs-strahlung process e+e- --> ZHH. The computation is performed with
the help of GRACE-loop. After subtraction of the initial state QED radiative
corrections, we find that the genuine weak corrections in the -scheme
are small for Higgs masses and energies where this cross section is largest and
is most likely to be studied. These corrections decrease with increasing
energies attaining about at TeV. The full order alpha
correction on the other hand is quite large at threshold but small at energies
around the peak. We also study changes in the shape of the invariant mass of
the Higgs pair which has been shown to be a good discriminating variable for
the measurement of the triple Higgs vertex in this reaction.Comment: 18 pages, 5 figures and 3 table
GRACE/SUSY Automatic Generation of Tree Amplitudes in the Minimal Supersymmetric Standard Model
GRACE/SUSY is a program package for generating the tree-level amplitude and
evaluating the corresponding cross section of processes of the minimal
supersymmetric extension of the standard model (MSSM). The Higgs potential
adopted in the system, however, is assumed to have a more general form
indicated by the two-Higgs-doublet model. This system is an extension of GRACE
for the standard model(SM) of the electroweak and strong interactions. For a
given MSSM process the Feynman graphs and amplitudes at tree-level are
automatically created. The Monte-Carlo phase space integration by means of
BASES gives the total and differential cross sections. When combined with
SPRING, an event generator, the program package provides us with the simulation
of the SUSY particle productions.Comment: 39 page, 1 figur
Full one-loop electroweak radiative corrections to single photon production in e+e-
Large scale calculation for the radiative corrections required for the
current and future collider experiments can be done automatically using the
GRACE-LOOP system. Here several results for e+e- --> 3-body processes are
presented including e+e- --> e+e-H and e+e- --> nu nubar gamma.Comment: 5 pages, contribution to ACAT03(Dec. 2003
Multi-leg calculations with the GRACE/1-LOOP system. --Toward Radiative Corrections to e+e- -> mu nu-bar u d-bar --
We performed the calculation of the full O(alpha) corrections to e+e- -> mu-
nu-bar u d-bar with the help of the GRACE/1-LOOP system. We discuss how a
finite decay width introduces a serious gauge invariance breaking, particularly
for infrared 5-point functions. This is related to the way the reduction of
those functions is performed and to the treatment of the width in the
reduction.Comment: 5 pages,invited talk at "Loops & Legs in Quantum Field Theory 2004",
Zinnowitz, Germany, April 200
QCD Corrections to Electroweak Vector Boson Scattering at Small Scattering Angles
We investigate the role of a certain class of QCD corrections to electroweak
vector boson scattering at small scattering angles and large energies. These
are present since, from the perturbative analysis, the vector bosons may
dissociate into quark-antiquark pairs giving rise to colour dipoles interacting
through gluon exchanges. After the computation of the vector boson impact
factors, we present expressions for the lowest order QCD scattering amplitude
and for the leading logarithmic BFKL amplitude. Particularly we discuss
numerical results for the process . The QCD corrections to
the cross section resulting from the interference with the electroweak ones are
estimated and compared with the leading pure electroweak part. Corrections
resulting from the leading log BFKL amplitude are of the order of few percent
already at the TeV energy range.Comment: 21 pages,9 figures, discussion on the helicity-flip impact factors
added, typos correcte
Jean-Baptiste Bélanger, hydraulic engineer, researcher and academic
Jean-Baptiste BÉLANGER (1790-1874) worked as a hydraulic engineer at the beginning of his career. He developed the backwater equation to calculate gradually-varied open channel flow properties for steady flow conditions. Later, as an academic at the leading French engineering schools (Ecole Centrale des Arts et Manufactures, Ecole des Ponts et Chaussées, and Ecole Polytechnique), he developed a new university curriculum in mechanics and several textbooks including a seminal text in hydraulic engineering. His influence on his contemporaries was considerable, and his name is written on the border of one of the four facades of the Eiffel Tower. BÉLANGER's leading role demonstrated the dynamism of practicing engineers at the time, and his contributions paved the way to many significant works in hydraulics
On SUSY GUTs with a degenerate Higgs mass matrix
Certain supersymmetric grand unified models predict that the coefficients of
the quadratic terms in the MSSM Higgs potential should be degenerate at the GUT
scale. We discuss some examples for such models, and we analyse the
implications of this peculiar condition of a GUT-scale degenerate Higgs mass
matrix for low-scale MSSM phenomenology. To this end we explore the parameter
space which is consistent with existing experimental constraints by means of a
Markov Chain Monte Carlo analysis.Comment: 31 pages, 27 figures; v2: typos correcte
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