121178348
Anomalous dimensions in background field gauges
Abstract Background field gauges, recently proposed for calculation of anomalous dimensions of operators in Wilson expansions in non-Abelian gauge theories, require the evaluation of extra diagrams. These diagrams are calculated and are found to give a correct gauge-invariant-mixing (unlike in Fermi-type gauges), but nevertheless the anomalous dimensions of the operators, owing to interesting cancellations, remain unchanged from those found in the Fermi gauges.
123114677
Mixing of operators in Wilson expansions
Abstract The tree-loop theorem of 't Hooft and Veltman is used in Fermi type gauges to show that gauge invariant operators in Wilson expansions mix in general with non-gauge invariant operators. Background field gauges are proposed in which this does not occur. Calculations of anomalous dimensions in these gauges are discussed.
8253414
The omega effect for neutral mesons
The possible role of decoherence due to space-time foam is discussed within the context of two models, one based on string/brane theory. and the other based on properties of black hole horizons in general relativity. It is argued that the density matrix satisfies a dissipative master equation, primarily from the study of renormalization group flows in non-critical string theory. This interpretation of the zero mode of the Liouville field as time leads necessarily to the CPT operator being ill defined. One striking consequence is that the quantum mechanical correlations of pair states of neutral mesons produced in meson factories are changed from the usual EPR state. The magnitude of this departure from EPR correlations is characterised by a parameter ω. The predicted value of ω is very small or zero. However it is shown explicitly that the the non-vanishing of ω is only a feature of the model based on string/brane theory.
115620347
The Schwinger mechanisms in non-abelian gauge theories
Abstract An alternative to the Higgs-Kibble mechanism for the formulation of spontaneously broken gauge theories has been recently proposed. It is shown how the new procedures can be generalised to the case when non-Abelian gauge groups are present.
120565281
Frustration and dynamics
Dynamical models incorporating frustration are discussed in general. In particular, it is shown how self-screening of Yang-Mills fields may lead to models of a generalized Ma-Rudnick genre for the spin-glass.
120412772
Renormalization-group approach to the lattice massive Schwinger model
Using Migdal-type recursion relations, the long-distance Coulomb force is found to be screened in the massive Schwinger model on a lattice. (AIP)
15196353
UV/IR MIXING IN NONCOMMUTATIVE FIELD THEORIES AND OPEN–CLOSED STRING DUALITY
In this paper we study the phenomenon of UV/IR mixing in noncommutative field theories from the point of view of worldsheet open–closed duality in string theory. New infrared divergences in noncommutative field theories arise as a result of integrating over high momentum modes in the loops. These are believed to come from integrating out additional bulk closed string modes. We analyze this issue in detail for the bosonic theory and further for the supersymmetric theory on the C2/Z2 orbifold. We elucidate on the exact role played by the constant background B-field in this correspondence.
107947607
RECENT DEVELOPMENTS IN THE TRIUMF CONTROL SYSTEM
The principle ideas and underlying architecture of the TRIUMF Central Control System have not changed since its commissioning in 1974. As described elsewhere 1,2,3 the system consists of a number of Data General minicomputers which communicate using a proprietary Data General parallel direct memory access interprocessor bus, and which share access to a common multiported memory containing a limited descriptive data base of device addresses and pointers to acquisition and conversion routines (Figure 1). The most important idea of the TRIUMF Control System design, and one which has in large measure determined the manner of its evolution, is the use of the executive crate, by means of which all central system computers share direct and immediate access to the entire seven parallel branch CAM.4C system, which in turn interfaces all accelerator devices and most of the main Control Room console devices. Expansion of the Control System to date has been realized on one hand by the addition of CAM.4C crates, and on the other by the addition of minicomputers to the executive crate interface. With the use of active extenders. the executive crate has been extended to three CAMAC crates. and could in principle clcctrically support as many as 1500 sources. In practice, this number is limited to a.bout 30 sources by bandwidth considerations, and to even fewer by the geographical requirement that sources be located physically within about 50 ft. (I/O bus length limitation) of the executive crate. This paper describes three recent developments in the TRIIJMF system whose designs have been influenced by its multisourced architecture. These are:
120714502
The Membrane Paradigm for Gauss-Bonnet gravity
We construct the membrane paradigm for black objects in Einstein-Gauss-Bonnet gravity in spacetime dimensions $ \ge 5$. As in the case of general relativity, for the observers outside the horizon the dynamics of the perturbations of the horizon can be modelled as a membrane endowed with fluid-like properties. We derive the stress-tensor for this membrane fluid and study the perturbation around static backgrounds with constant curvature horizon cross-section to express the stress tensor in the form of a Newtonian viscous fluid with pressure, shear viscosity and bulk viscosity. The ratio of the shear viscosity and the entropy density is shown to generically violate the bound suggested by Policastro, Son and Starinets. We evaluate the transport coefficients for some static geometries. For the black brane geometry our results match with those available in the literature. For the spherically symmetric AdS black hole our results can be interpreted as a holographic prediction for the transport coefficients and viscosity to the entropy density ratio for the dual conformal field theory living on the boundary, $S^3 \times R$.
119340528
Aspects of open-closed duality in a background B-field
We study closed string exchanges in background B-field. By analysing the two point one loop amplitude in bosonic string theory, we show that tree-level exchange of lowest lying, tachyonic and massless closed string modes, have IR singularities similar to those of the nonplanar sector in noncommutative gauge theories. We further isolate the contributions from each of the massless modes. We interpret these results as the manifestation of open/closed string duality, where the IR behaviour of the boundary noncommutative gauge theory is reconstructed from the bulk theory of closed strings.
121582631
Dark energy, cosmic coincidence and future singularity of the universe
Dark energy model with the equation of state $$p_{DE} =-\rho _{DE} -A\rho _{DE}^\alpha $$, is characterised by four finite life time future singularity of the universe for different values of the parameter $$A$$ and $$\alpha $$ [Nojiri et al. in Phys Rev D 71:063004, 2005]. Since from the matter dominated era to the dark energy dominated era the ratio of the dark energy density to the matter energy density increases as the universe expand for these future singularities, the universe passes through a significant time when the dark energy density and the matter energy density are nearly comparable. Considering $$\frac{1}{r_0 }<r=\frac{\rho _{DE} }{\rho _M }<r_0 $$, where $$r_0$$ is any fixed ratio, we calculate the fraction of total life time of the universe when the universe passes through the coincidental stage for these singularities. It has been found that the fractional time varies as $$\alpha $$ varies within the range for which these finite life time future singularities occur and the fraction is smaller for smaller values of $$r_0 $$. Importance of the fractional time and observational limits onto the values of the parameter $$A$$ and $$\alpha $$ has also been discussed.