778 research outputs found
Production of Long-Lived Sleptons at LHC
We analyse the MSSM parameter space and discuss the narrow band near the
so-called co-annihilation region where sleptons may be long-lived particles.
This region is consistent with the WMAP restrictions on the Dark matter and
depends on the value of . In this region staus are long-lived and
may go through the detector. Due to a relatively small mass (150 850
GeV) their production cross-section at LHC may reach a few % pb.Comment: LaTex, 8 pages, 6 eps figure
B-meson signatures of a Supersymmetric U(2) flavor model
We discuss B-meson signatures of a Supersymmetric U(2) flavor model, with
relatively light (electroweak scale masses) third generation right-handed
scalars. We impose current B and K meson experimental constraints on such a
theory, and obtain expectations for B->X_s gamma, B->X_s glue, B->X_s l+ l-,
B->phi K_s, B_s-B_sbar mixing, and the dilepton asymmetry in B_s. We show that
such a theory is compatible with all current data, and furthermore, could
reconcile the apparent deviations from Standard Model predictions that have
been found in some experiments.Comment: 37 pages, 21 figures, RevTeX4; v.2 - minor modifications to improve
readability. Published versio
The Indirect Limit on the Standard Model Higgs Boson Mass from the Precision FERMILAB, LEP and SLD Data
Standard Model fits are performed on the most recent leptonic and b quark Z
decay data from LEP and SLD, and FERMILAB data on top quark production, to
obtain and . Poor fits are obtained, with confidence levels
2%. Removing the b quark data improves markedly the quality of the fits and
reduces the 95% CL upper limit on by 50 GeV.Comment: 6 pages 3 tables i figur
QCD Corrections in two-Higgs-doublet extensions of the Standard Model with Minimal Flavor Violation
We present the QCD corrections to R_b and to the Delta B=1 effective
Hamiltonian in models with a second Higgs field that couples to the quarks
respecting the criterion of Minimal Flavor Violation, thus belonging either to
the (1,2)_1/2 or to the (8,2)_1/2 representation of SU(3)xSU(2)xU(1). After the
inclusion of the QCD corrections, the prediction for R_b becomes practically
insensitive to the choice of renormalization scheme for the top mass, which for
the type-I and type-II models translates in a more robust lower bound on
tan(beta). The QCD-corrected determinations of Rb and BR(B->Xs gamma) are used
to discuss the constraints on the couplings of a (colored) charged Higgs boson
to top and bottom quarks.Comment: 19 pages, 7 figures. v2: version published in Phys. Rev. D, with
additional reference and not
On the NLO QCD corrections to the production of the heaviest neutral Higgs scalar in the MSSM
We present a calculation of the two-loop top-stop-gluino contributions to
Higgs production via gluon fusion in the MSSM. By means of an asymptotic
expansion in the heavy particle masses, we obtain explicit and compact analytic
formulae that are valid when the Higgs and the top quark are lighter than stops
and gluino, without assuming a specific hierarchy between the Higgs mass and
the top mass. Being applicable to the heaviest Higgs scalar in a significant
region of the MSSM parameter space, our results complement earlier ones
obtained with a Taylor expansion in the Higgs mass, and can be easily
implemented in computer codes to provide an efficient and accurate
determination of the Higgs production cross section.Comment: 18 pages, 4 figure
Weak Interaction Sum Rules for Polarized top-antitop Production at LHC
We consider two polarization asymmetries in the process of top-antitop
production at LHC. We show that the theoretical predictions for these two
quantities, at the strong and electroweak partonic one-loop level, are free of
QCD and QED effects. At this perturbative level we derive two sum rules, that
relate measurable quantities of top-antitop production to genuinely weak
inputs. This would allow to perform two independent tests of the candidate
theoretical model, with a precision that will be fixed by the future
experimental accuracies of the different polarization measurements. A tentative
quantitative illustration of this statement for a specific MSSM scenario is
enclosed, and a generalization to include two other future realistic
measurements is also proposed.Comment: 13 pages, 3 figures, local report number adde
Very Constrained Minimal Supersymmetric Standard Models
We consider very constrained versions of the minimal supersymmetric extension
of the Standard Model (VCMSSMs) which, in addition to constraining the scalar
masses m_0 and gaugino masses m_{1/2} to be universal at some input scale,
impose relations between the trilinear and bilinear soft supersymmetry breaking
parameters A_0 and B_0. These relations may be linear, as in simple minimal
supergravity models, or nonlinear, as in the Giudice-Masiero mechanism for
generating the Higgs-mixing mu term. We discuss the application of the
electroweak vacuum conditions in VCMSSMs, which may be used to make a
prediction for tan beta as a function of m_0 and m_{1/2} that is usually
unique. We baseline the discussion of the parameter spaces allowed in VCMSSMs
by updating the parameter space allowed in the CMSSM for fixed values of tan
beta with no relation between A_0 and B_0 assumed {\it a priori}, displaying
contours of B_0 for a fixed input value of A_0, incorporating the latest CDF/D0
measurement of m_t and the latest BNL measurement of g_mu - 2. We emphasize
that phenomenological studies of the CMSSM are frequently not applicable to
specific VCMSSMs, notably those based on minimal supergravity, which require
m_0 = m_{3/2} as well as A_0 = B_0 + m_0. We then display (m_{1/2}, m_0) planes
for selected VCMSSMs, treating in a unified way the parameter regions where
either a neutralino or the gravitino is the LSP. In particular, we examine in
detail the allowed parameter space for the Giudice-Masiero model.Comment: 26 pages, 32 eps figure
Electroweak Precision Data and Gravitino Dark Matter
Electroweak precision measurements can provide indirect information about the
possible scale of supersymmetry already at the present level of accuracy. We
review present day sensitivities of precision data in mSUGRA-type models with
the gravitino as the lightest supersymmetric particle (LSP). The chi^2 fit is
based on M_W, sin^2 theta_eff, (g-2)_mu, BR(b -> s gamma) and the lightest MSSM
Higgs boson mass, M_h. We find indications for relatively light soft
supersymmetry-breaking masses, offering good prospects for the LHC and the ILC,
and in some cases also for the Tevatron.Comment: 4 pages, 1 figure. Talk given at the LCWS06 March 2006, Bangalore,
India. References adde
Effect of cytochalasin B on the induction of chromosome missegregation by colchicine at low concentrations in human lymphocytes
The aim of the present work was to investigate the possible interference of cytochalasin B (cyt B) with low concentration treatment with colchicine in the induction of chromosome/chromatid loss and micronuclei in human lymphocytes mitotically activated in vitro. Thus, cells from a single female donor were treated with colchicine (10 or 25 nM, from 24 h after PHA addition to fixation at 66 h) either in the presence or absence of cyt B. Single lagging chromosomes/chromatids were scored in bipolar ana-telophases and greater damage (disrupted and c-anaphases) was scored in cells at anaphase. Micronuclei were scored in the first 4000 nuclei observed in both cyt B-treated (in mononucleate and binucleate cells) and untreated cultures. With the same criterion, FISH analysis was performed on 2000 nuclei where chromosome 7 and 11 centromeric DNA probes were used in pairs. Our results showed that: (i) the frequency of laggards and of micronuclei increased with colchicine concentration but in the presence of cyt B there was a lower frequency of both (with a mean reduction of ~ 49%); (ii) FISH analysis showed a colchicine concentration-dependent increase in nuclei with three spots for chromosome 7; (iii) a colchicine concentration-dependent increase in tetraploid cells was observed. This increase was particularly remarkable (5-fold) in cells grown in the presence of cyt B compared with cyt B-untreated cells. The observed 'cyt B effects' can be explained if it is assumed that in cytokinesis-blocked cells there is a shorter distance between the poles. As a consequence: (i) laggards would be engulfed in the nearest daughter nucleus with a consequent lower induction of micronuclei; (ii) segregating sister chromatids in heavily impaired anaphases would not travel a sufficient distance to give rise to two daughter nuclei, leading to an increased frequency of polyploid nuclei
Indirect mitotic nondisjunction in Vicia faba and Chinese hamster cells
The hypothesis of indirect mitotic nondisjunction was tested in plant and mammalian cells. This hypothesis states that micronuclei derived from lagging chromosomes or chromatids are able to perform DNA synthesis and undergo mitotic condensation synchronously with main nuclei. Hence, as chromosomes, they can be moved to spindle poles together with the chromosomes of the main nuclei during mitosis. In that way chromosomes "lost" as micronuclei can be reincorporated in the main nuclei. In order to test this, both Vicia faba meristematic cells and cells of a Chinese hamster line (Cl-1) were treated with low doses of colchicine. Mitotic anomalies, micronuclei and cells with a polyploid or aneuploid karyotype were scored at different fixation times. A detailed analysis was performed on single chromosome misdistributions, as well as on micronuclei and cells with aneuploid karyotypes derived from single chromosome misdistributions. Indirect mitotic nondisjunction was shown to play a primary role in the origin of aneuploid karyotypes in Vicia faba, but not in Cl-1 cells
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