Loop scattering in two-dimensional QCD

Using the integrability conditions that we recently obtained in QCD$_2$ with massless fermions, we arrive at a sufficient number of conservation laws to be able to fix the scattering amplitudes involving a local version of the Wilson loop operator.Comment: 6 pages, plain tex

Re-Operations: A Two Year Experience at Gezira National Centre for Pediatric Surgery-Sudan

Background: The development of pediatric surgical care in Africa has suffered from the neglecance of health policy makers, yet surgery remains an essential component of basic healthcare and an important means of providing preventive and curative treatment. Although the Sudan started with very few specialists who were trained in pediatric surgery to overcome the need of this specialty which started in the late of 70th and early of 1980th with only 5 surgeons.Re-operative surgery in pediatric patients is a challenge that is confronted by every surgeon, a particular operation may be initially done and followed by appropriate post-operative care, functional or anatomical problem may need further surgical intervention. Objective:  To evaluate the magnitude of re-operation in pediatric patients seen at GNCPS. Methods: This is a retrospective and prospective descriptive hospital based study that was conducted over two years as from March 2014 to Feb2016 at GNCPS. The study includes all pediatric surgical patients who needed a redo surgery.  Result: The number of patients studied were111.The age distribution of studied group, the most common age group was less than 5year( n= 78) patients representing 70.3 %, followed by age group 6-10 year (n=19) 17.1% and the last age group 11-15(n=14) 12.6%. The ratio of male to female is 5.16:1. 61.3 %( n=68) of patients from the rural areas while 38.7% (n=32) from urban areas. The person who did the first operation: 47.7% (n=53) were done by pediatric surgeons, 28.8% (n=32) operated by registrars 18% (n=20) done by medical officers, 5.4% (n=6) operated by general surgeons. The final outcome of the patients: 49.5% (n=55) of them were alive without complications 35.1% (n=39) alive with complications, Number of patients who died were 15.3% (n=17). Conclusion: The majority of redo-operations are done under the age of 5year. Less than 50% of the initial operations were done by specialized pediatric surgeons reflecting the gross shortage of surgeons in this discipline. More than 80% of initial operations were done at specialized centers reflecting the poor set-up at the center. The gastrointestinal (GIT) system was associated with the most surgical redo. The mortality following redo-operations was high

Thermodynamics and collapse of self-gravitating Brownian particles in D dimensions

We address the thermodynamics (equilibrium density profiles, phase diagram, instability analysis...) and the collapse of a self-gravitating gas of Brownian particles in D dimensions, in both canonical and microcanonical ensembles. In the canonical ensemble, we derive the analytic form of the density scaling profile which decays as f(x)=x^{-\alpha}, with alpha=2. In the microcanonical ensemble, we show that f decays as f(x)=x^{-\alpha_{max}}, where \alpha_{max} is a non-trivial exponent. We derive exact expansions for alpha_{max} and f in the limit of large D. Finally, we solve the problem in D=2, which displays rather rich and peculiar features

Spectrum of confining strings in SU(N) gauge theories

We study the spectrum of the confining strings in four-dimensional SU(N) gauge theories. We compute, for the SU(4) and SU(6) gauge theories formulated on a lattice, the string tensions sigma_k related to sources with Z_N charge k, using Monte Carlo simulations. Our results are consistent with the sine formula sigma_k/sigma = sin k pi/N / sin pi/N for the ratio between sigma_k and the standard string tension sigma. For the SU(4) and SU(6) cases the accuracy is approximately 1% and 2%, respectively. The sine formula is known to emerge in various realizations of supersymmetric SU(N) gauge theories. On the other hand, our results show deviations from Casimir scaling. We also discuss an analogous behavior exhibited by two-dimensional SU(N) x SU(N) chiral models.Comment: Latex, 34 pages, 10 figures. Results of new SU(4) simulations added. The new data are included in the analysis, leading to improved final estimates for SU(4). Conclusions unchange

Quantum phase properties of two-mode Jaynes-Cummings model for Schr\"odinger-cat states: interference and entanglement

In this paper we investigate the quantum phase properties for the coherent superposition states (Schr\"odinger-cat states) for two-mode multiphoton Jaynes-Cummings model in the framework of the Pegg-Barnett formalism. We also demonstrate the behavior of the Wigner ($W$) function at the phase space origin. We obtain many interesting results such as there is a clear relationship between the revival-collapse phenomenon occurring in the atomic inversion (as well as in the evolution of the $W$ function) and the behavior of the phase distribution of both the single-mode and two-mode cases. Furthermore, we find that the phase variances of the single-mode case can exhibit revival-collapse phenomenon about the long-time behavior. We show that such behavior occurs for interaction time several times smaller than that of the single-mode Jaynes-Cummings model.Comment: 23, 8 figure

Self-gravitating Brownian particles in two dimensions: the case of N=2 particles

We study the motion of N=2 overdamped Brownian particles in gravitational interaction in a space of dimension d=2. This is equivalent to the simplified motion of two biological entities interacting via chemotaxis when time delay and degradation of the chemical are ignored. This problem also bears some similarities with the stochastic motion of two point vortices in viscous hydrodynamics [Agullo & Verga, Phys. Rev. E, 63, 056304 (2001)]. We analytically obtain the density probability of finding the particles at a distance r from each other at time t. We also determine the probability that the particles have coalesced and formed a Dirac peak at time t (i.e. the probability that the reduced particle has reached r=0 at time t). Finally, we investigate the variance of the distribution and discuss the proper form of the virial theorem for this system. The reduced particle has a normal diffusion behaviour for small times with a gravity-modified diffusion coefficient =r_0^2+(4k_B/\xi\mu)(T-T_*)t, where k_BT_{*}=Gm_1m_2/2 is a critical temperature, and an anomalous diffusion for large times ~t^(1-T_*/T). As a by-product, our solution also describes the growth of the Dirac peak (condensate) that forms in the post-collapse regime of the Smoluchowski-Poisson system (or Keller-Segel model) for T<T_c=GMm/(4k_B). We find that the saturation of the mass of the condensate to the total mass is algebraic in an infinite domain and exponential in a bounded domain.Comment: Revised version (20/5/2010) accepted for publication in EPJ

Counting Domain Walls in N=1 Super Yang-Mills Theory

We study the multiplicity of BPS domain walls in N=1 super Yang-Mills theory, by passing to a weakly coupled Higgs phase through the addition of fundamental matter. The number of domain walls connecting two specified vacuum states is then determined via the Witten index of the induced worldvolume theory, which is invariant under the deformation to the Higgs phase. The worldvolume theory is a sigma model with a Grassmanian target space which arises as the coset associated with the global symmetries broken by the wall solution. Imposing a suitable infrared regulator, the result is found to agree with recent work of Acharya and Vafa in which the walls were realized as wrapped D4-branes in IIA string theory.Comment: 28 pages, RevTeX, 3 figures; v2: discussion of the index slightly expanded, using an alternative regulator, and references added; v3: typos corrected, to appear in Phys. Rev.

Black hole solutions in F(R) gravity with conformal anomaly

In this paper, we consider $F(R)=R+f(R)$ theory instead of Einstein gravity with conformal anomaly and look for its analytical solutions. Depending on the free parameters, one may obtain both uncharged and charged solutions for some classes of $F(R)$ models. Calculation of Kretschmann scalar shows that there is a singularity located at $r=0$, which the geometry of uncharged (charged) solution is corresponding to the Schwarzschild (Reissner-Nordstr\"om) singularity. Further, we discuss the viability of our models in details. We show that these models can be stable depending on their parameters and in different epoches of the universe.Comment: 12 pages, one figur