13,803 research outputs found
Quadratic Contributions of Softly Broken Supersymmetry in the Light of Loop Regularization
Loop regularization (LORE) is a novel regularization scheme in modern quantum
field theories. It makes no change to the spacetime structure and respects both
gauge symmetries and supersymmetry. As a result, LORE should be useful in
calculating loop corrections in supersymmetry phenomenology. To demonstrate
further its power, in this article we revisit in the light of LORE the old
issue of the absence of quadratic contributions (quadratic divergences) in
softly broken supersymmetric field theories. It is shown explicitly by Feynman
diagrammatic calculations that up to two loops the Wess-Zumino model with soft
supersymmetry breaking terms (WZ' model), one of the simplest models with the
explicit supersymmetry breaking, is free of quadratic contributions. All the
quadratic contributions cancel with each other perfectly, which is consistent
with results dictated by the supergraph techniques.Comment: 25 pages, 3 figures; accepted versio
Quantum Electroweak Symmetry Breaking Through Loop Quadratic Contributions
Based on two postulations that (i) the Higgs boson has a large bare mass GeV at the characteristic energy scale which defines
the standard model (SM) in the ultraviolet region, and (ii) quadratic
contributions of Feynman loop diagrams in quantum field theories are physically
meaningful, we show that the SM electroweak symmetry breaking is induced by the
quadratic contributions from loop effects. As the quadratic running of Higgs
mass parameter leads to an additive renormalization, which distinguishes from
the logarithmic running with a multiplicative renormalization, the symmetry
breaking occurs once the sliding energy scale moves from down to a
transition scale at which the additive renormalized Higgs
mass parameter gets to change the sign. With the input of
current experimental data, this symmetry breaking energy scale is found to be
GeV, which provides another basic energy scale for the
SM besides . Studying such a symmetry breaking mechanism could play an
important role in understanding both the hierarchy problem and naturalness
problem. It also provides a possible way to explore the experimental
implications of the quadratic contributions as lies within the
probing reach of the LHC and the future Great Collider.Comment: 10 pages, 2 figures, published versio
Palatini formulation of gravity theory, and its cosmological implications
We consider the Palatini formulation of gravity theory, in which a
nonminimal coupling between the Ricci scalar and the trace of the
energy-momentum tensor is introduced, by considering the metric and the affine
connection as independent field variables. The field equations and the
equations of motion for massive test particles are derived, and we show that
the independent connection can be expressed as the Levi-Civita connection of an
auxiliary, energy-momentum trace dependent metric, related to the physical
metric by a conformal transformation. Similarly to the metric case, the field
equations impose the non-conservation of the energy-momentum tensor. We obtain
the explicit form of the equations of motion for massive test particles in the
case of a perfect fluid, and the expression of the extra-force, which is
identical to the one obtained in the metric case. The thermodynamic
interpretation of the theory is also briefly discussed. We investigate in
detail the cosmological implications of the theory, and we obtain the
generalized Friedmann equations of the gravity in the Palatini
formulation. Cosmological models with Lagrangians of the type and are investigated. These models lead to
evolution equations whose solutions describe accelerating Universes at late
times.Comment: 22 pages, no figures, accepted for publication in EPJC; references
adde
Sound speed of a Bose-Einstein condensate in an optical lattice
The speed of sound of a Bose-Einstein condensate in an optical lattice is
studied both analytically and numerically in all three dimensions. Our
investigation shows that the sound speed depends strongly on the strength of
the lattice. In the one-dimensional case, the speed of sound falls
monotonically with increasing lattice strength. The dependence on lattice
strength becomes much richer in two and three dimensions. In the
two-dimensional case, when the interaction is weak, the sound speed first
increases then decreases as the lattice strength increases. For the three
dimensional lattice, the sound speed can even oscillate with the lattice
strength. These rich behaviors can be understood in terms of compressibility
and effective mass. Our analytical results at the limit of weak lattices also
offer an interesting perspective to the understanding: they show the lattice
component perpendicular to the sound propagation increases the sound speed
while the lattice components parallel to the propagation decreases the sound
speed. The various dependence of the sound speed on the lattice strength is the
result of this competition.Comment: 15pages 6 figure
Research on basis of reverse genetics system of a Sindbis-like virus XJ-160
As a Sindbis-like virus (SINLV), XJ-160 virus was isolated from a pooled sample of Anopheles mosquitoes collected in Xinjiang, China, in 1990. Recombinant plasmid pBR-XJ160 is an infectious full-length cDNA clone of XJ-160 virus, from which rescued virus BR-XJ160 can be obtained by transcription in vitro and transfection. The BR-XJ160 virus raised in BHK-21 cells was indistinguishable from the XJ-160 virus in its biological properties, including its plaque morphology, growth kinetics and suckling mouse neurovirulence. On basis of pBR-XJ160, the effects of substitutions within nonstructural protein 1 (nsP1) or nsP2 on the infectivity and pathogenesis of Sindbis virus (SINV) have been investigated. We have also confirmed the essential role of E2 glycoprotein, especially the domain of 145-150 (amino acid) aa, in SINV infection through the interaction with cellular heparan sulfate (HS). In addition, we have developed XJ-160 virus-based vector system, including replicon vector, defective helper (DH) plasmids and the packaging cell lines (PCLs). Here we provide an update of main development in the field concerned with XJ-160 virus
- …