1,026 research outputs found
Contact interaction probes at the Linear Collider with polarized electron and positron beams
For contact-interaction searches at the Linear Collider, we discuss the
advantages of polarizing both the electron and the positron beams as compared
with polarizing only the electron beam. In particular, for the processes
e^+e^-\to \mu^+\mu^-, \tau^+\tau^-, b\bar{b} and c\bar{c} at a future e^+e^-
collider with \sqrt{s}=0.5 TeV we derive model-independent bounds on the
four-fermion contact interaction parameters from studies of the helicity cross
sections.Comment: 1+15 pages, LaTeX2e, including 7 figure
Contact interactions and polarized beams at a Linear Collider
We discuss contact-interaction searches in the processes e^+e^-\to
\mu^+\mu^-, b\bar{b} and c\bar{c} at an e^+e^- Linear Collider with c.m. energy
\sqrt{s}=0.5 TeV and with longitudinally polarized beams. The measurement of
polarized cross sections allows to study the individual helicity cross
sections, and consequently to derive separate, model-independent, constraints
on the four-fermion contact interaction couplings. We evaluate the reach on
those parameters foreseeable in the case of both electron and positron
polarization fixed at some reference values, and compare it with the situation
where only electron polarization is available. The analysis is based on
polarized integrated cross sections with optimal kinematical cuts that can
improve the sensitivity to the relevant couplings. While electron polarization
would by itself allow such an analysis, the additional positron polarization
(with no loss of beam intensity) and optimization can have a crucial role in
improving the sensitivity to the new interactions.Comment: 13 pages, LaTeX, including figure
An extended hybrid magnetohydrodynamics gyrokinetic model for numerical simulation of shear Alfv\'en waves in burning plasmas
Adopting the theoretical framework for the generalized fishbonelike
dispersion relation, an extended hybrid magnetohydrodynamics gyrokinetic
simulation model has been derived analytically by taking into account both
thermal ion compressibility and diamagnetic effects in addition to energetic
particle kinetic behaviors. The extended model has been used for implementing
an eXtended version of Hybrid Magnetohydrodynamics Gyrokinetic Code (XHMGC) to
study thermal ion kinetic effects on Alfv\'enic modes driven by energetic
particles, such as kinetic beta induced Alfv\'en eigenmodes in tokamak fusion
plasmas
Structure formation in modified gravity models alternative to dark energy
We study structure formation in phenomenological models in which the
Friedmann equation receives a correction of the form
, which realize an accelerated expansion without
dark energy. In order to address structure formation in these model, we
construct simple covariant gravitational equations which give the modified
Friedmann equation with where is an integer. For , the
underlying theory is known as a 5D braneworld model (the DGP model). Thus the
models interpolate between the DGP model () and the LCDM model
in general relativity (). Using the covariant
equations, cosmological perturbations are analyzed. It is shown that in order
to satisfy the Bianchi identity at a perturbative level, we need to introduce a
correction term in the effective equations. In the DGP model,
comes from 5D gravitational fields and correct conditions on
can be derived by solving the 5D perturbations. In the general
case , we have to assume the structure of a modified theory of gravity to
determine . We show that structure formation is different from a
dark energy model in general relativity with identical expansion history and
that quantitative features of the difference crucially depend on the conditions
on , that is, the structure of the underlying theory of modified
gravity. This implies that it is essential to identify underlying theories in
order to test these phenomenological models against observational data and,
once we identify a consistent theory, structure formation tests become
essential to distinguish modified gravity models from dark energy models in
general relativity.Comment: 12 pages, 3 figure
Adiabatic and non-adiabatic perturbations for loop quantum cosmology
We generalize the perturbations theory of loop quantum cosmology to a
hydrodynamical form and define an effective curvature perturbation on an
uniform density hypersurfaces . As in the classical cosmology,
should be gauge-invariant and conservation on the large scales. The
evolutions of both the adiabatic and the non-adiabatic perturbations for a
multi-fluids model are investigated in the framework of the effective
hydrodynamical theory of loop quantum cosmology with the inverse triad
correction. We find that, different from the classical cosmology, the evolution
of the large-scales non-adiabatic entropy perturbation can be driven by an
adiabatic curvature perturbation and this adiabatic source for the
non-adiabatic perturbation is a quantum effect. As an application of the
related formalism, we study a decay model and give out the numerical results.Comment: 10 pages, 3 figure
Excitation of superconducting qubits from hot non-equilibrium quasiparticles
Superconducting qubits probe environmental defects such as non-equilibrium
quasiparticles, an important source of decoherence. We show that "hot"
non-equilibrium quasiparticles, with energies above the superconducting gap,
affect qubits differently from quasiparticles at the gap, implying qubits can
probe the dynamic quasiparticle energy distribution. For hot quasiparticles, we
predict a non-neligable increase in the qubit excited state probability P_e. By
injecting hot quasiparticles into a qubit, we experimentally measure an
increase of P_e in semi-quantitative agreement with the model and rule out the
typically assumed thermal distribution.Comment: Main paper: 5 pages, 5 figures. Supplement: 1 page, 1 figure, 1
table. Updated to user-prepared accepted version. Key changes: Supplement
added, Introduction rewritten, Figs.2,3,5 revised, Fig.4 adde
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