46,983 research outputs found
Novel vortex structures in dipolar condensates
We investigate the properties of single vortices and of vortex lattice in a
rotating dipolar condensate. We show that vortices in this system possess many
novel features induced by the long-range anisotropic dipolar interaction
between particles. For example, when the dipoles are polarized along the
rotation axis, vortices may display a crater-like structure; when dipoles are
polarized orthogonal to the rotation axis, vortex cores takes an elliptical
shape and the vortex lattice no longer possesses hexagonal symmetry.Comment: 4 pages, 5 figure
Exploring Resonant di-Higgs production in the Higgs Singlet Model
We study the enhancement of the di-Higgs production cross section resulting
from the resonant decay of a heavy Higgs boson at hadron colliders in a model
with a Higgs singlet. This enhancement of the double Higgs production rate is
crucial in understanding the structure of the scalar potential and we determine
the maximum allowed enhancement such that the electroweak minimum is a global
minimum. The di-Higgs production enhancement can be as large as a factor of ~
18 (13) for the mass of the heavy Higgs around 270 (420) GeV relative to the
Standard Model rate at 14 TeV for parameters corresponding to a global
electroweak minimum.Comment: 25 pages, 14 figures. Version approved for publication. Discussion of
Z2 symmetric limit improved and references adde
Top Partners and Higgs Boson Production
The Higgs boson is produced at the LHC through gluon fusion at roughly the
Standard Model rate. New colored fermions, which can contribute to
, must have vector-like interactions in order not to be in
conflict with the experimentally measured rate. We examine the size of the
corrections to single and double Higgs production from heavy vector-like
fermions in singlets and doublets and search for regions of parameter
space where double Higgs production is enhanced relative to the Standard Model
prediction. We compare production rates and distributions for double Higgs
production from gluon fusion using an exact calculation, the low energy theorem
(LET), where the top quark and the heavy vector-like fermions are taken to be
infinitely massive, and an effective theory (EFT) where top mass effects are
included exactly and the effects of the heavy fermions are included to . Unlike the LET, the EFT gives an extremely accurate description
of the kinematic distributions for double Higgs production.Comment: 37 pages, 11 figures. Minor changes to Figs. 8-1
Hardcore bosons on checkerboard lattices near half filling: geometric frustration, vanishing charge order and fractional phase
We study a spinless hardcore boson model on checkerboard lattices by Green
function Monte Carlo method. At half filling, the ground state energy is
obtained up to lattice and extrapolated to infinite size, the
staggered pseudospin magnetization is found to vanish in the thermodynamic
limit. Thus the charge order is absent in this system. Away from
half filling, two defects induced by each hole (particle) may carry fractional
charge (). For one hole case, we study how the defect-defect
correlation changes with , which is the ratio between the hopping integral
and cyclic exchange, equals to when . Moreover, we argue that
these fractional defects may propagate independently when the concentration of
holes (or defects) is large enough
Probing dipolar effects with condensate shape oscillation
We discuss the low energy shape oscillations of a magnetic trapped atomic
condensate including the spin dipole interaction. When the nominal isotropic
s-wave interaction strength becomes tunable through a Feshbach resonance (e.g.
as for Rb atoms), anisotropic dipolar effects are shown to be detectable
under current experimental conditions [E. A. Donley {\it et al.}, Nature {\bf
412}, 295 (2001)].Comment: revised version, submitte
Dipolar effect in coherent spin mixing of two atoms in a single optical lattice site
We show that atomic dipolar effects are detectable in the system that
recently demonstrated two-atom coherent spin dynamics within individual lattice
sites of a Mott state. Based on a two-state approximation for the two-atom
internal states and relying on a variational approach, we have estimated the
spin dipolar effect. Despite the absolute weakness of the dipole-dipole
interaction, it is shown that it leads to experimentally observable effects in
the spin mixing dynamics.Comment: 4 pages, 3 color eps figures, to appear in Phys. Rev. Let
Interacting dark energy, holographic principle and coincidence problem
The interacting and holographic dark energy models involve two important
quantities. One is the characteristic size of the holographic bound and the
other is the coupling term of the interaction between dark energy and dark
matter. Rather than fixing either of them, we present a detailed study of
theoretical relationships among these quantities and cosmological parameters as
well as observational constraints in a very general formalism. In particular,
we argue that the ratio of dark matter to dark energy density depends on the
choice of these two quantities, thus providing a mechanism to change the
evolution history of the ratio from that in standard cosmology such that the
coincidence problem may be solved. We investigate this problem in detail and
construct explicit models to demonstrate that it may be alleviated provided
that the interacting term and the characteristic size of holographic bound are
appropriately specified. Furthermore, these models are well fitted with the
current observation at least in the low red-shift region.Comment: 20 pages, 3 figure
Heavy Color-Octet Particles at the LHC
Many new-physics models, especially those with a color-triplet top-quark
partner, contain a heavy color-octet state. The "naturalness" argument for a
light Higgs boson requires that the color-octet state be not much heavier than
a TeV, and thus it can be pair-produced with large cross sections at
high-energy hadron colliders. It may decay preferentially to a top quark plus a
top-partner, which subsequently decays to a top quark plus a color-singlet
state. This singlet can serve as a WIMP dark-matter candidate. Such decay
chains lead to a spectacular signal of four top quarks plus missing energy. We
pursue a general categorization of the color-octet states and their decay
products according to their spin and gauge quantum numbers. We review the
current bounds on the new states at the LHC and study the expected discovery
reach at the 8-TeV and 14-TeV runs. We also present the production rates at a
future 100-TeV hadron collider, where the cross sections will be many orders of
magnitude greater than at the 14-TeV LHC. Furthermore, we explore the extent to
which one can determine the color octet's mass, spin, and chiral couplings.
Finally, we propose a test to determine whether the fermionic color octet is a
Majorana particle.Comment: 20 pages, 9 figures; journal versio
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