925 research outputs found
Dynamical Symmetry Breaking With a Fourth Generation
Adding a fourth generation to the Standard Model and assuming it to be valid
up to some cutoff \Lambda, we show that electroweak symmetry is broken by
radiative corrections due to the fourth generation. The effects of the fourth
generation are isolated using a Lagrangian with a genuine scalar without
self-interactions at the classical level. For masses of the fourth generation
consistent with electroweak precision data (including the B \rightarrow K \pi\
CP asymmetries) we obtain a Higgs mass of the order of a few hundreds GeV and a
cutoff \Lambda\ around 1-2 TeV. We study the reliability of the perturbative
treatment used to obtain these results taking into account the running of the
Yukawa couplings of the fourth quark generation with the aid of the
Renormalization Group (RG) equations, finding similar allowed values for the
Higgs mass but a slightly lower cut-off due to the breaking of the perturbative
regime. Such low cut-off means that the effects of new physics needed to
describe electroweak interactions at energy above \Lambda\ should be measurable
at the LHC. We use the minimal supersymmetric extension of the standard model
with four generations as an explicit example of models realizing the dynamical
electroweak symmetry breaking by radiative corrections and containing new
physics. Here, the cutoff is replaced by the masses of the squarks and
electroweak symmetry breaking by radiative corrections requires the squark
masses to be of the order of 1 TeV.Comment: 20 pages, 7 figures. New section adde
Effect of Wavefunction Renormalisation in N-Flavour Qed3 at Finite Temperature
A recent study of dynamical chiral symmetry breaking in N-flavour QED at
finite temperature is extended to include the effect of fermion wavefunction
renormalisation in the Schwinger-Dyson equations. The simple ``zero-frequency''
truncation previously used is found to lead to unphysical results, especially
as . A modified set of equations is proposed, whose solutions behave
in a way which is qualitatively similar to the solutions of Pennington et
al. [5-8] who have made extensive studies of the effect of wavefunction
renormalisation in this context, and who concluded that there was no critical
(at T=0) above which chiral symmetry was restored. In contrast, we find
that our modified equations predict a critical at , and an
phase diagram very similar to the earlier study neglecting wavefunction
renormalisation. The reason for the difference is traced to the different
infrared behaviour of the vacuum polarisation at and at .Comment: 17 pages + 13 figures (available upon request), Oxford preprint
OUTP-93-30P, IFUNAM preprint FT94-39, LaTe
Dynamical Mass Generation in a Finite-Temperature Abelian Gauge Theory
We write down the gap equation for the fermion self-energy in a
finite-temperature abelian gauge theory in three dimensions. The instantaneous
approximation is relaxed, momentum-dependent fermion and photon self-energies
are considered, and the corresponding Schwinger-Dyson equation is solved
numerically. The relation between the zero-momentum and zero-temperature
fermion self-energy and the critical temperature T_c, above which there is no
dynamical mass generation, is then studied. We also investigate the effect
which the number of fermion flavours N_f has on the results, and we give the
phase diagram of the theory with respect to T and N_f.Comment: 20 LaTeX pages, 4 postscript figures in a single file, version to
appear in Physical Review
Rotating light, OAM paradox and relativistic complex scalar field
Recent studies show that the angular momentum, both spin and orbital, of
rotating light beams possesses counter-intuitive characteristics. We present a
new approach to the question of orbital angular momentum of light based on the
complex massless scalar field representation of light. The covariant equation
for the scalar field is treated in rotating system using the general
relativistic framework. First we show the equivalence of the U(1) gauge current
for the scalar field with the Poynting vector continuity equation for paraxial
light, and then apply the formalism to the calculation of the orbital angular
momentum of rotating light beams. If the difference between the co-, contra-,
and physical quantities is properly accounted for there does not result any
paradox in the orbital angular momentum of rotating light. An artificial
analogue of the paradoxical situation could be constructed but it is wrong
within the present formalism. It is shown that the orbital angular momentum of
rotating beam comprising of modes with opposite azimuthal indices corresponds
to that of rigid rotation. A short review on the electromagnetism in
noninertial systems is presented to motivate a fully covariant Maxwell field
approach in rotating system to address the rotating light phenomenon.Comment: No figure
Effective action for QED in 2+1 dimensions at finite temperature
We calculate the effective action for a constant magnetic field and a
time-dependent time-component of the gauge field in 2+1 dimensions at finite
temperature. We also discuss the behaviour of the charge density and the
fermion condensate as order parameters of symmetry breaking.Comment: Latex, 10 pages, no figure
Effect of gauge boson mass on the phase structure of QED
Dynamical chiral symmetry breaking (DCSB) in QED with finite gauge
boson mass is
studied in the framework of the rainbow approximation of Dyson-Schwinger
equations.
By adopting a simple gauge boson propagator ansatz at finite temperature, we
first numerically solve the
Dyson-Schwinger equation for the fermion self-energy to
determine the chiral phase diagram of QED with finite gauge boson mass
at finite chemical potential and finite temperature, then we study the
effect of the finite gauge mass on the phase diagram of QED. It is found
that the gauge boson mass suppresses the occurrence of
DCSB. The area of the region in the chiral phase diagram corresponding to
DCSB phase decreases as
the gauge boson mass increases. In
particular, chiral symmetry gets restored when is above a
certain critical value. In this paper, we use DCSB to describe the
antiferromagnetic order and use the gauge boson mass to describe the
superconducting order. Our results give qualitatively a physical
picture on the competition and coexistence between antiferromagnetic
order and superconducting orders in high temperature cuprate superconductors.Comment: 10 pages, 2 figure
The role of karyopherins in the regulated sumoylation of septins
In the yeast Saccharomyces cerevisiae, several components of the septin ring are sumoylated during anaphase and then abruptly desumoylated at cytokinesis. We show that septin sumoylation is controlled by the interactions of two enzymes of the sumoylation pathway, Siz1p and Ulp1p, with the nuclear transport machinery. The E3 ligase Siz1p is imported into the nucleus by the karyopherin Kap95p during interphase. In M phase, Siz1p is exported from the nucleus by the karyopherin Kap142p/Msn5p and subsequently targeted to the septin ring, where it participates in septin sumoylation. We also show that the accumulation of sumoylated septins during mitosis is dependent on the interactions of the SUMO isopeptidase Ulp1p with Kap121p and Kap95p–Kap60p and the nuclear pore complex (NPC). In addition to sequestering Ulp1 at the NPC, Kap121p is required for targeting Ulp1p to the septin ring during mitosis. We present a model in which Ulp1p is maintained at the NPC during interphase and transiently interacts with the septin ring during mitosis
- …