330 research outputs found
Measuring effective electroweak couplings in single top production at the LHC
We study the mechanism of single top production at the LHC in the framework
of an effective electroweak Lagrangian, analyzing the sensitivity of different
observables to the magnitude of the effective couplings that parametrize new
physics beyond the Standard Model. The observables relevant to the distinction
between left and right effective couplings involve in practice the measurement
of the spin of the top and this can be achieved only indirectly by measuring
the angular distribution of its decay products. We show that the presence of
effective right-handed couplings implies that the top is not in a pure spin
state. A unique spin basis is singled out which allows one to connect top decay
products angular distribution with the polarized top differential cross
section. We present a complete analytical expression of the differential
polarized cross section of the relevant perturbative subprocess including
general effective couplings. The mass of the bottom quark, which actually turns
out to be more relevant than naively expected, is retained. Finally we analyze
different aspects the total cross section relevant to the measurement of new
physics through the effective couplings. The above analysis also applies to
anti-top production in a straightforward way.Comment: 38 pages, 17 figure
Assessing the Biohazard Potential of Putative Martian Organisms for Exploration Class Human Space Missions
Exploration Class missions to Mars will require precautions against potential contamination by any native microorganisms that may be incidentally pathogenic to humans. While the results of NASA's Viking biology experiments of 1976 have been generally interpreted as inconclusive for surface organisms, the possibility of native surface life has never been ruled out and more recent studies suggest that the case for biological interpretation of the Viking Labeled Release data may now be stronger than it was when the experiments were originally conducted. It is possible that, prior to the first human landing on Mars, robotic craft and sample return missions will provide enough data to know with certainty whether or not future human landing sites harbor extant life forms. However, if native life is confirmed, it will be problematic to determine whether any of its species may present a medical risk to astronauts. Therefore, it will become necessary to assess empirically the risk that the planet contains pathogens based on terrestrial examples of pathogenicity and to take a reasonably cautious approach to bio-hazard protection. A survey of terrestrial pathogens was conducted with special emphasis on those pathogens whose evolution has not depended on the presence of animal hosts. The history of the development and implementation of Apollo anticontamination protocol and recent recommendations of the NRC Space Studies Board regarding Mars were reviewed. Organisms can emerge in nature in the absence of indigenous animal hosts and both infectious and non-infectious human pathogens are theoretically possible on Mars. The prospect of Martian surface life, together with the existence of a diversity of routes by which pathogenicity has emerged on Earth, suggests that the possibility of human pathogens on Mars, while low, is not zero. Since the discovery and study of Martian life can have long-term benefits for humanity, the risk that Martian life might include pathogens should not be an obstacle to human exploration. As a precaution, however, it is recommended that EVA suits be decontaminated when astronauts enter surface habitats when returning from field activity and that biosafety protocol approximating laboratory BSL 2 be developed for astronauts working in laboratories on the Martian surface. Quarantine of astronauts and Martian materials arriving on Earth should also be part of a human Mars mission and this and the surface biosafety program should be integral to human expeditions from the earliest stages of the mission planning
Hadron Collider Signatures for New Interactions of Top and Bottom Quarks
One of the main goals for hadron colliders is the study of the properties of
the third generation quarks. We study the signatures for new TeV resonances
that couple to top or bottom quarks both at the Tevatron Run II and at the LHC.
We find that in the simplest production processes of Drell-Yan type at the
Tevatron, the signals are overwhelmed by QCD backgrounds. We also find that it
is possible to study these resonances when they are produced in association
with a pair of heavy quarks or in association with a single top at the LHC.In
particular, with an integrated luminosity of 300 fb at the LHC, it is
possible to probe resonance masses up to around 2 TeV.Comment: 24 pages, 15 figures, Minor corrections, version to appear in Phys.
Rev.
Searching for a light Fermiophobic Higgs Boson at the Tevatron
We propose new production mechanisms for light fermiophobic Higgs bosons
() with suppressed couplings to vector bosons () at the Fermilab
Tevatron. These mechanisms (e.g. ) are complementary to the
conventional process , which suffers from a strong suppression of
in realistic models with a . The new mechanisms extend the
coverage at the Tevatron Run II to the larger region, and offer the
possibility of observing new event topologies with up to 4 photons.Comment: 15 pages, including 5 eps-figure
Single top production associated with a neutral scalar at LHC in topcolor-assisted technicolor
The topcolor-assisted technicolor (TC2) model predicts a number of neutral
scalars like the top-pion () and the top-Higgs (). These
scalars have flavor-changing neutral-current (FCNC) top quark couplings, among
which the top-charm transition couplings may be sizable. Such FCNC couplings
induce single top productions associated with a neutral scalar at the CERN
Large Hadron Collider (LHC) through the parton processes and
. In this note we examine these productions and find their
production rates can exceed the sensitivity of the LHC in a large
part of parameter space. Since in the Standard Model and the minimal
supersymmetric model such rare productions have unobservably small production
rates at the LHC, these rare processes will serve as a good probe for the TC2
model.Comment: 7 pages, 3 fig
Single Top Production as a Window to Physics Beyond the Standard Model
Production of single top quarks at a high energy hadron collider is studied
as a means to identify physics beyond the standard model related to the
electroweak symmetry breaking. The sensitivity of the -channel mode,
the -channel -gluon fusion mode, and the \tw mode to various possible
forms of new physics is assessed, and it is found that the three modes are
sensitive to different forms of new physics, indicating that they provide
complimentary information about the properties of the top quark. Polarization
observables are also considered, and found to provide potentially useful
information about the structure of the interactions of top.Comment: References added and minor discussion improvements; results
unchanged; Version to be published in PR
Genes regulated by estrogen in breast tumor cells in vitro are similarly regulated in vivo in tumor xenografts and human breast tumors
BACKGROUND: Estrogen plays a central role in breast cancer pathogenesis. Although many studies have characterized the estrogen regulation of genes using in vitro cell culture models by global mRNA expression profiling, it is not clear whether these genes are similarly regulated in vivo or how they might be coordinately expressed in primary human tumors. RESULTS: We generated DNA microarray-based gene expression profiles from three estrogen receptor α (ERα)-positive breast cancer cell lines stimulated by 17β-estradiol (E2) in vitro over a time course, as well as from MCF-7 cells grown as xenografts in ovariectomized athymic nude mice with E2 supplementation and after its withdrawal. When the patterns of genes regulated by E2 in vitro were compared to those obtained from xenografts, we found a remarkable overlap (over 40%) of genes regulated by E2 in both contexts. These patterns were compared to those obtained from published clinical data sets. We show that, as a group, E2-regulated genes from our preclinical models were co-expressed with ERα in a panel of ERα+ breast tumor mRNA profiles, when corrections were made for patient age, as well as with progesterone receptor. Furthermore, the E2-regulated genes were significantly enriched for transcriptional targets of the myc oncogene and were found to be coordinately expressed with Myc in human tumors. CONCLUSION: Our results provide significant validation of a widely used in vitro model of estrogen signaling as being pathologically relevant to breast cancers in vivo
Two-loop Barr-Zee type Contributions to in the MSSM
We consider the contribution of a two-loop Barr-Zee type diagram to
in the minimal supersymmetric standard model (MSSM). At relatively
large , we show that the contribution of light third generation
scalar fermions and neutral CP-even Higgs, , can easily explain the
very recent BNL experimental data. In our analysis prefers negative
and positive . It is more sensitive to the chirality flipping
h^0(H^0)\wt{f}_R^*\wt{f}_L rather than chirality conserving couplings.Comment: 10 pages, 5 figures, references adde
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