3,213 research outputs found
Neutral scalar Higgs bosons in the USSM at the LHC
We study the possibility of discovering neutral scalar Higgs bosons in the
-extended supersymmetric standard model (USSM) at the CERN Large Hadron
Collider (LHC), by examining their productions via the exotic quark loop in the
gluon fusion process at leading order. It is possible in some parameter region
that the neutral scalar Higgs bosons may have stronger couplings with the
exotic quarks than with top quark. In this case, the exotic quarks may
contribute more significantly than top quark in productions of the neutral
scalar Higgs bosons in the gluon fusion process. We find that there is indeed
some parameter region in the USSM that supports our speculations.Comment: 18 pages; changed content; JPhys
Quasi-particle scattering and protected nature of topological states in a parent topological insulator BiSe
We report on angle resolved photoemission spectroscopic studies on a parent
topological insulator (TI), BiSe. The line width of the spectral
function (inverse of the quasi-particle lifetime) of the topological metallic
(TM) states shows an anomalous behavior. This behavior can be reasonably
accounted for by assuming decay of the quasi-particles predominantly into bulk
electronic states through electron-electron interaction and defect scattering.
Studies on aged surfaces reveal that topological metallic states are very much
unaffected by the potentials created by adsorbed atoms or molecules on the
surface, indicating that topological states could be indeed protected against
weak perturbations.Comment: accepted for publication in Phys. Rev. B(R
Numerical study of 1.1 GeV electron acceleration over a-few-millimeter-long plasma with a tapered density
We present two-dimensional particle-in-cell simulations of laser wakefield electron acceleration up to 1.1 GeV over a-few-millimeter-long plasma with the help of density tapering. We observed that, in a uniform plasma, the electron beam reaches the dephasing state not only by the slow phase velocity of the wakefield but also by the relativistic prolonging of the plasma wavelength. Such a dephasing between the wakefield and beam can be mitigated by an upward density taper. By employing a parabolically increasing plasma density, we obtained a significant enhancement of the beam energy from 850 MeV (uniform) to 1.1 GeV (tapered). However, the similar relativistically promoted dephasing was observed again in the environment of tapered density. Over a few millimeters the driving laser pulse was well self-guided without any externally prepared channel. Thus, this parameter regime is suitable for the gas-jet laser wakefield electron acceleration experiments.open6
Time-reversal symmetry breaking in circuit-QED based photon lattices
Breaking time-reversal symmetry is a prerequisite for accessing certain
interesting many-body states such as fractional quantum Hall states. For
polaritons, charge neutrality prevents magnetic fields from providing a direct
symmetry breaking mechanism and similar to the situation in ultracold atomic
gases, an effective magnetic field has to be synthesized. We show that in the
circuit QED architecture, this can be achieved by inserting simple
superconducting circuits into the resonator junctions. In the presence of such
coupling elements, constant parallel magnetic and electric fields suffice to
break time-reversal symmetry. We support these theoretical predictions with
numerical simulations for realistic sample parameters, specify general
conditions under which time-reversal is broken, and discuss the application to
chiral Fock state transfer, an on-chip circulator, and tunable band structure
for the Kagome lattice.Comment: minor revisions, version published in PRA; 19 pages, 13 figures, 2
table
Effective thermodynamics of strongly coupled qubits
Interactions between a quantum system and its environment at low temperatures
can lead to violations of thermal laws for the system. The source of these
violations is the entanglement between system and environment, which prevents
the system from entering into a thermal state. On the other hand, for two-state
systems, we show that one can define an effective temperature, placing the
system into a `pseudo-thermal' state where effective thermal laws are upheld.
We then numerically explore these assertions for an n-state system inspired by
the spin-boson environment.Comment: 9 pages, 3 figure
Giant Magnetoelectric Effect in a Multiferroic Material with a High Ferroelectric Transition Temperature
We present a unique example of giant magnetoelectric effect in a conventional
multiferroic HoMnO3, where polarization is very large (~56 mC/m2) and the
ferroelectric transition temperature is higher than the magnetic ordering
temperature by an order. We attribute the uniqueness of the giant
magnetoelectric effect to the ferroelectricity induced entirely by the
off-center displacement of rare earth ions with large magnetic moments. This
finding suggests a new avenue to design multiferroics with large polarization
and higher ferroelectric transition temperature as well as large
magnetoelectric effects
Reconstruction of plasma density profiles by measuring spectra of radiation emitted from oscillating plasma dipoles
We suggest a new method for characterising non-uniform density distributions of plasma by measuring the spectra of radiation emitted from a localised plasma dipole oscillator excited by colliding electromagnetic pulses. The density distribution can be determined by scanning the collision point in space. Two-dimensional particle-in-cell simulations demonstrate the reconstruction of linear and nonlinear density profiles corresponding to laser-produced plasma. The method can be applied to a wide range of plasma, including fusion and low temperature plasmas. It overcomes many of the disadvantages of existing methods that only yield average densities along the path of probe pulses, such as interferometry and spectroscopy
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