2,153 research outputs found
Debajyoti Choudhury
Gluon fusion into a very heavy neutrino pair by Higgs exchange is shown to
lead to substantial production cross sections at supercolliders even
without any extra generation of quarks. Rates are calculated for scalar as well
as pseudoscalar Higgs. The angular correlation between dileptons emerging from
the decays of the neutrinos shows distinctive features for Dirac and Majorana
neutrinos as well as for scalar and pseudoscalar Higgs
Periodic solutions of second order Hamiltonian systems bifurcating from infinity
The goal of this article is to study closed connected sets of periodic
solutions, of autonomous second order Hamiltonian systems, emanating from
infinity. The main idea is to apply the degree for SO(2)-equivariant gradient
operators defined by the second author. Using the results due to Rabier we show
that we cannot apply the Leray-Schauder degree to prove the main results of
this article. It is worth pointing out that since we study connected sets of
solutions, we also cannot use the Conley index technique and the Morse theory.Comment: 24 page
Pregnant women become insensitive to cold stress
BACKGROUND: The function of the hypothalamic-pituitary-adrenal (HPA) axis is known to be altered during pregnancy, but it has not been tested with a natural stressor. METHODS: A group of pregnant women (n = 10) were tested towards the end of pregnancy (mean 36.8 ± 2.5 weeks gestation) and about 8 weeks postpartum (mean 7.8 ± 1.5 weeks), together with a matched control group, with a one minute cold hand stressor test. Saliva samples were collected before and 10 and 20 minutes after the test, and stored for later radioimmunoassay of cortisol. RESULTS: The control group showed a highly significant response to the test. The pregnant group showed no response, and the postpartum group a variable but non significant one CONCLUSIONS: This shows that the HPA axis becomes hypofunctional to a natural stressor at the end of pregnancy. It is suggested that one possible evolutionary function for this is to protect the fetus from the stress responses of the mother
Quarkonium Production at High-Energy Colliders
The theoretical description of heavy quarkonium production at high-energy
p-pbar and e-p colliders is reviewed. Predictions based on non-relativistic QCD
factorisation are confronted with recent charmonium and bottomonium data from
the Tevatron and HERA. Potential shortcomings of the present theoretical
analyses are discussed, and the prospects for quarkonium physics at the
upgraded Tevatron and HERA colliders and at the LHC are summarised.Comment: 61 pages, 20 figures. To be published in Progress in Particle and
Nuclear Physics, Vol. 47, issue
QCD corrections to the production of at the ILC
A precise calculation of the top quark pair production associated with a hard
photon is essential for testing the electroweak property of the top quark in
the Standard Model (SM). We investigate the one-loop QCD corrections to the
process at the International Linear Collider
(ILC), and find that the -factor can be as large as 1.238 (1.105, 1.060) for
a center-of-mass energy GeV. The transverse momentum
distributions of the top quark and photon are respectively shown at leading
order (LO) and next-to-leading order(NLO). Due to the asymmetric rapidity
distribution of the top (anti-top) quark, we also study the top quark
forward-backward asymmetry () in production at
NLO, which is found to be 45.82 (55.25, 55.89)% for
GeV.Comment: 12 pages, 5 figures, version acceptd by Phys. Lett.
Quantum control of proximal spins using nanoscale magnetic resonance imaging
Quantum control of individual spins in condensed matter systems is an
emerging field with wide-ranging applications in spintronics, quantum
computation, and sensitive magnetometry. Recent experiments have demonstrated
the ability to address and manipulate single electron spins through either
optical or electrical techniques. However, it is a challenge to extend
individual spin control to nanoscale multi-electron systems, as individual
spins are often irresolvable with existing methods. Here we demonstrate that
coherent individual spin control can be achieved with few-nm resolution for
proximal electron spins by performing single-spin magnetic resonance imaging
(MRI), which is realized via a scanning magnetic field gradient that is both
strong enough to achieve nanometric spatial resolution and sufficiently stable
for coherent spin manipulations. We apply this scanning field-gradient MRI
technique to electronic spins in nitrogen-vacancy (NV) centers in diamond and
achieve nanometric resolution in imaging, characterization, and manipulation of
individual spins. For NV centers, our results in individual spin control
demonstrate an improvement of nearly two orders of magnitude in spatial
resolution compared to conventional optical diffraction-limited techniques.
This scanning-field-gradient microscope enables a wide range of applications
including materials characterization, spin entanglement, and nanoscale
magnetometry.Comment: 7 pages, 4 figure
Higgs-pair Production and Decay in Simplest Little Higgs Model
In the framework of the simplest little Higgs model (SLHM), we study the
production of a pair of neutral CP-even Higgs bosons at the LHC. First, we
examine the production rate and find that it can be significantly larger than
the SM prediction. Then we investigate the decays of the Higgs-pair and find
that for a low Higgs mass their dominant decay mode is hh->\eta\eta\eta\eta
(\eta is a CP-odd scalar) while hh->b\bar{b}\eta\eta and hh->\eta\eta WW may
also have sizable ratios. Finally, we comparatively study the rates of pp-> hh
-> b\bar{b}\tau^+ \tau^-, pp->hh->b\bar{b}\gamma\gamma, and pp->hh->WWWW in the
SLHM and the littlest Higgs models (LHT). We find that for a light Higgs,
compared with the SM predictions, all the three rates can be sizably enhanced
in the LHT but severely suppressed in the SLHM; while for an intermediately
heavy Higgs, both the LHT and SLHM can enhance sizably the SM predictions.Comment: Version in Nucl. Phys.
- …