90 research outputs found
Noncommutative N=1 super Yang-Mills, the Seiberg-Witten map and UV divergences
Classically, the dual under the Seiberg-Witten map of noncommutative U(N),
{\cal N}=1 super Yang-Mills theory is a field theory with ordinary gauge
symmetry whose fields carry, however, a \theta-deformed nonlinear realisation
of the {\cal N}=1 supersymmetry algebra in four dimensions. For the latter
theory we work out at one-loop and first order in the noncommutative parameter
matrix \theta^{\mu\nu} the UV divergent part of its effective action in the
background-field gauge, and, for N>=2, we show that for finite values of N the
gauge sector fails to be renormalisable; however, in the large N limit the full
theory is renormalisable, in keeping with the expectations raised by the
quantum behaviour of the theory's noncommutative classical dual. We also obtain
--for N>=3, the case with N=2 being trivial-- the UV divergent part of the
effective action of the SU(N) noncommutative theory in the enveloping-algebra
formalism that is obtained from the previous ordinary U(N) theory by removing
the U(1) degrees of freedom. This noncommutative SU(N) theory is also
renormalisable.Comment: 33 pages, 4 figures. Version 2: Unnecessary files removed. Version 3:
New types of field redefinitions were considered, which make the large N U(N)
and the SU(N) theories renormalisable. The conclusions for U(N) with finite N
remain unchanged. Version 4: Corrected mistyped equations, minor revision
Spherically Symmetric Noncommutative Space: d = 4
In order to find a noncommutative analog of Schwarzschild or
Schhwarzschild-de Sitter blackhole we investigate spherically symmetric spaces
generated by four noncommutative coordinates in the frame formalism. We present
two solutions which however do not posess the prescribed commutative limit. Our
analysis indicates that the appropriate noncommutative space might be found as
a subspace of a higher-dimensional space.Comment: 14 page
Metric approach to quantum constraints
A new framework for deriving equations of motion for constrained quantum
systems is introduced, and a procedure for its implementation is outlined. In
special cases the framework reduces to a quantum analogue of the Dirac theory
of constrains in classical mechanics. Explicit examples involving spin-1/2
particles are worked out in detail: in one example our approach coincides with
a quantum version of the Dirac formalism, while the other example illustrates
how a situation that cannot be treated by Dirac's approach can nevertheless be
dealt with in the present scheme.Comment: 13 pages, 1 figur
Inhibitory effect of coumarin derivatives on apple (cv. Idared) polyphenol oxidase
Inhibitory effect of 32 coumarin derivatives (20 Schiff bases, 5 thiosemicarbazides, 5 thiazolidinones, and their precursors,
7-hydroxy-4-methylcoumarin and 4-methylcoumarin-7-yl hydrazine carboxylate) on partially purified apple polyphenol oxidase was investigated. Thirteen coumarin derivatives inhibited polyphenol oxidase (5 Schiff bases, 5 thiosemicarbazides,
1 thiazolidinone, 4-methyl-7-hydroxycoumarin and 4-methylcoumarin-7-yl hydrazine carboxylate), while 19 derivatives showed no effect on enzyme activity. The most effective inhibitors were thiosemicarbazides, with 4-methyl-1-(2-(4-methyl-2-oxo-2H-chromen-7-yloxy)acetyl) thiosemicarbazide (compound C23) being the most prominent inhibitor (IC50 = 10.45 µM). The importance of thiosemicarbazide moiety as crucial structure element for strong apple PPO inhibition was confirmed by its cyclisation to thiazolidinone bearing the same substituents as corresponding thiosemicarbazide. Capture of the sulphur atom of thiosemicarbazide group within tiazolidinone ring caused significant loss of inhibitory effect against apple PPO
Emergence of classical behavior from the quantum spin
Classical Hamiltonian system of a point moving on a sphere of fixed radius is
shown to emerge from the constrained evolution of quantum spin. The constrained
quantum evolution corresponds to an appropriate coarse-graining of the quantum
states into equivalence classes, and forces the equivalence classes to evolve
as single units representing the classical states. The coarse-grained quantum
spin with the constrained evolution in the limit of the large spin becomes
indistinguishable from the classical system
TeV Scale Implications of Non Commutative Space time in Laboratory Frame with Polarized Beams
We analyze , and processes within the
Seiberg-Witten expanded noncommutative scenario using polarized beams. With
unpolarized beams the leading order effects of non commutativity starts from
second order in non commutative(NC) parameter i.e. , while with
polarized beams these corrections appear at first order () in cross
section. The corrections in Compton case can probe the magnetic
component() while in Pair production and Pair annihilation
probe the electric component() of NC parameter. We include the
effects of earth rotation in our analysis. This study is done by investigating
the effects of non commutativity on different time averaged cross section
observables. The results which also depends on the position of the collider,
can provide clear and distinct signatures of the model testable at the
International Linear Collider(ILC).Comment: 22 pages, 19 figures, new comments and references added, few typos
corrected, Published in JHE
Mean field approximation of two coupled populations of excitable units
The analysis on stability and bifurcations in the macroscopic dynamics
exhibited by the system of two coupled large populations comprised of
stochastic excitable units each is performed by studying an approximate system,
obtained by replacing each population with the corresponding mean-field model.
In the exact system, one has the units within an ensemble communicating via the
time-delayed linear couplings, whereas the inter-ensemble terms involve the
nonlinear time-delayed interaction mediated by the appropriate global
variables. The aim is to demonstrate that the bifurcations affecting the
stability of the stationary state of the original system, governed by a set of
4N stochastic delay-differential equations for the microscopic dynamics, can
accurately be reproduced by a flow containing just four deterministic
delay-differential equations which describe the evolution of the mean-field
based variables. In particular, the considered issues include determining the
parameter domains where the stationary state is stable, the scenarios for the
onset and the time-delay induced suppression of the collective mode, as well as
the parameter domains admitting bistability between the equilibrium and the
oscillatory state. We show how analytically tractable bifurcations occurring in
the approximate model can be used to identify the characteristic mechanisms by
which the stationary state is destabilized under different system
configurations, like those with symmetrical or asymmetrical inter-population
couplings.Comment: 5 figure
On divergent 3-vertices in noncommutative SU(2)gauge theory
We analyze divergencies in 2-point and 3-point functions for noncommutative
-expanded SU(2)-gauge theory with massless fermions. We show that,
after field redefinition and renormalization of couplings, one divergent term
remains.Comment: 7 page
On UV/IR mixing in noncommutative gauge field theories
In formulating gauge field theories on noncommutative (NC) spaces it is
suggested that particles carrying gauge invariant quantities should not be
viewed as pointlike, but rather as extended objects whose sizes grow linearly
with their momenta. This and other generic properties deriving from the
nonlocal character of interactions (showing thus unambiguously their
quantum-gravity origin) lead to a specific form of UV/IR mixing as well as to a
pathological behavior at the quantum level when the noncommutativity parameter
theta is set to be arbitrarily small. In spite of previous suggestions that in
a NC gauge theory based on the theta-expanded Seiberg-Witten (SW) maps UV/IR
mixing effects may be under control, a fairly recent study of photon
self-energy within a SW theta-exact approach has shown that UV/IR mixing is
still present. We study the self-energy contribution for neutral fermions in
the theta-exact approach of NC QED, and show by explicit calculation that all
but one divergence can be eliminated for a generic choice of the
noncommutativity parameter theta. The remaining divergence is linked to the
pointlike limit of an extended object.Comment: 10 pages, a figure added, version to appear in JHE
The absence of the 4 divergence in noncommutative chiral models
In this paper we show that in the noncommutative chiral gauge theories the
4-fermion vertices are finite. The -vertices appear in linear order in
quantization of the -expanded noncommutative gauge theories; in all
previously considered models, based on Dirac fermions, the -vertices
were divergent and nonrenormalizable.Comment: 7 page
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