244 Matching Results

Search Results

Advanced search parameters have been applied.

String Field Equations from Generalized Sigma Model

Description: We propose a new approach for deriving the string field equations from a general sigma model on the world-sheet. This approach leads to an equation which combines some of the attractive features of both the renormalization group method and the covariant beta function treatment of the massless excitations. It has the advantage of being covariant under a very general set of both local and non-local transformations in the field space. We apply it to the tachyon, massless and first massive level, and show that the resulting field equations reproduce the correct spectrum of a left-right symmetric closed bosonic string.
Date: January 29, 1997
Creator: Bardakci, K. & Bernardo, L.M.
Partner: UNT Libraries Government Documents Department

RG analysis of magnetic catalysis in dynamical symmetry breaking

Description: We perform the renormalization group analysis on the dynamical symmetry breaking under strong external magnetic field, studied recently by Gusynin, Miransky and Shovkovy. We find that any attractive four-Fermi interaction becomes strong in the low energy, thus leading to dynamical symmetry breaking. When the four-Fermi interaction is absent, the {beta}-function for the electromagnetic coupling vanishes in the leading order in 1/N. By solving the Schwinger-Dyson equation for the fermion propagator, we show that in 1/N expansion, for any electromagnetic coupling, dynamical symmetry breaking occurs due to the presence of Landau energy gap by the external magnetic field. 5 refs.
Date: May 1, 1996
Creator: Hong, Deog Ki & Kim, Youngman
Partner: UNT Libraries Government Documents Department

Size reduction of complex networks preserving modularity

Description: The ubiquity of modular structure in real-world complex networks is being the focus of attention in many trials to understand the interplay between network topology and functionality. The best approaches to the identification of modular structure are based on the optimization of a quality function known as modularity. However this optimization is a hard task provided that the computational complexity of the problem is in the NP-hard class. Here we propose an exact method for reducing the size of weighted (directed and undirected) complex networks while maintaining invariant its modularity. This size reduction allows the heuristic algorithms that optimize modularity for a better exploration of the modularity landscape. We compare the modularity obtained in several real complex-networks by using the Extremal Optimization algorithm, before and after the size reduction, showing the improvement obtained. We speculate that the proposed analytical size reduction could be extended to an exact coarse graining of the network in the scope of real-space renormalization.
Date: December 24, 2008
Creator: Arenas, A.; Duch, J.; Fernandez, A. & Gomez, S.
Partner: UNT Libraries Government Documents Department

Traveling waves and the renormalization group improvedBalitsky-Kovchegov equation

Description: I study the incorporation of renormalization group (RG)improved BFKL kernels in the Balitsky-Kovchegov (BK) equation whichdescribes parton saturation. The RG improvement takes into accountimportant parts of the next-to-leading and higher order logarithmiccorrections to the kernel. The traveling wave front method for analyzingthe BK equation is generalized to deal with RG-resummed kernels,restricting to the interesting case of fixed QCD coupling. The resultsshow that the higher order corrections suppress the rapid increase of thesaturation scale with increasing rapidity. I also perform a "diffusive"differential equation approximation, which illustrates that someimportant qualitative properties of the kernel change when including RGcorrections.
Date: December 1, 2006
Creator: Enberg, Rikard
Partner: UNT Libraries Government Documents Department


Description: We present results at {beta} = 6.0 and 6.2 for the O(a) improvement and renormalization constants for bilinear operators using axial and vector Ward identities. We discuss the extraction of the mass dependence of the renormalization constants and the coefficients of the equation of motion operators.
Date: December 1, 2000
Partner: UNT Libraries Government Documents Department

Renormalization of currents for massive fermions

Description: The renormalization of vector and axial-vector currents for massive fermions (in the ''Fermilab formalism'') is discussed. We give results for non-degenerate masses, which are needed for semi-leptonic form factors.
Date: December 1, 1998
Creator: Hashimoto, Andreas S. Kronfeld and Shoji
Partner: UNT Libraries Government Documents Department

Bandgap renormalization: GaAs/AlGaAs quantum wells

Description: Bandgap energy renormalization by many-body interactions has been studied in a series of n-type 8-nm-wide GaAs/AlGaAs single quantum wells using magnetoluminescence spectroscopy at 1.4K and for magnetic fields up to 30T. The 2D- carrier densities varied between 1 and 12 x 10(11) cm(-2). At the maximum 2D-carrier density, the bandgap energy difference between the doped and undoped samples was about 34 meV.
Date: January 1, 1998
Creator: Jones, E.D.; Blount, M.; Chow, W.; Hou, H.; Simmons, J.A.; Kim, Yongmin et al.
Partner: UNT Libraries Government Documents Department

Reduction of Quark Mass Scheme Dependence in B bar -> Xs gamma at the NNLL Level

Description: The uncertainty of the theoretical prediction of the B {yields} X{sub s}{gamma} branching ratio at NLL level is dominated by the charm mass renormalization scheme ambiguity. In this paper we calculate those NNLL terms which are related to the renormalization of m{sub c}, in order to get an estimate of the corresponding uncertainty at the NNLL level. We find that these terms significantly reduce (by typically a factor of two) the error on BR(B {yields} X{sub s}{gamma}) induced by the definition of m{sub c}. Taking into account the experimental accuracy of around 10% and the future prospects of the B factories, we conclude that a NNLL calculation would increase the sensitivity of the observable B {yields} X{sub s}{gamma} to possible new degrees of freedom beyond the SM significantly.
Date: June 20, 2005
Creator: Asatrian, H.M.; Inst., /Yerevan Phys.; Greub, C.; U., /Bern; Hovhannisyan, A.; Inst., /Yerevan Phys. et al.
Partner: UNT Libraries Government Documents Department

Nucleon matrix elements with Nf=2+1+1 maximally twisted fermions

Description: We present the first lattice calculation of nucleon matrix elements using four dynamical flavors. We use the Nf=2+1+1 maximally twisted mass formulation. The renormalization is performed non-perturbatively in the RI'-MOM scheme and results are given for the vector and axial vector operators with up to one-derivative. Our calculation of the average momentum of the unpolarized non-singlet parton distribution is presented and compared to our previous results obtained from the Nf=2 case.
Date: June 1, 2010
Creator: Simon Dinter, Constantia Alexandrou, Martha Constantinou, Vincent Drach, Karl Jansen, Dru Renner
Partner: UNT Libraries Government Documents Department

Charge independence, charge symmetry breaking in the S-wave nucleon-nucleon interaction, and renormalization

Description: We study the interplay between charge symmetry breaking and renormalization in the NN system for S-waves. We find a set of universality relations which disentangle explicitly the known long distance dynamics from low energy parameters and extend them to the Coulomb case. We analyze within such an approach the One-Boson-Exchange potential and the theoretical conditions which allow to relate the proton-neutron, proton-proton and neutron-neutron scattering observables without the introduction of extra new parameters and providing good phenomenological success.
Date: February 1, 2012
Creator: Alvaro Calle Cordon,Manuel Pavon Valderrama,Enrique Ruiz Arriola
Partner: UNT Libraries Government Documents Department

Supersymmetry, Naturalness, and Signatures at the LHC

Description: Weak scale supersymmetry is often said to be fine-tuned, especially if the matter content is minimal. This is not true if there is a large A term for the top squarks. We present a systematic study on fine-tuning in minimal supersymmetric theories and identify low energy spectra that do not lead to severe fine-tuning. Characteristic features of these spectra are: a large A term for the top squarks, small top squark masses, moderately large tan {beta}, and a small {mu} parameter. There are classes of theories leading to these features, which are discussed. In one class, which allows a complete elimination of fine-tuning, the Higgsinos are the lightest among all the superpartners of the standard model particles, leading to three nearly degenerate neutralino/chargino states. This gives interesting signals at the LHC--the dilepton invariant mass distribution has a very small endpoint and shows a particular shape determined by the Higgsino nature of the two lightest neutralinos. We demonstrate that these signals are indeed useful in realistic analyses by performing Monte Carlo simulations, including detector simulations and background estimations. We also present a method that allows the determination of all the relevant superparticle masses without using input from particular models, despite the limited kinematical information due to short cascades. This allows us to test various possible models, which is demonstrated in the case of a model with mixed moduli-anomaly mediation. We also give a simple derivation of special renormalization group properties associated with moduli mediated supersymmetry breaking, which are relevant in a model without fine-tuning.
Date: February 10, 2006
Creator: Kitano, Ryuichiro & Nomura, Yasunori
Partner: UNT Libraries Government Documents Department

Review of Upscaling Methods for Describing Unsaturated Flow

Description: Representing samll-scale features can be a challenge when one wants to model unsaturated flow in large domains. In this report, the various upscaling techniques are reviewed. The following upscaling methods have been identified from the literature: stochastic methods, renormalization methods, volume averaging and homogenization methods. In addition, a final technique, full resolution numerical modeling, is also discussed.
Date: September 26, 2000
Creator: Wood, Brian D.
Partner: UNT Libraries Government Documents Department

A new scheme for the running coupling constant in gauge theories using Wilson loops

Description: We propose a new renormalization scheme of the running coupling constant in general gauge theories defined by using the Wilson loops. The renormalized coupling constant is obtained from the Cretz ratio in lattice simulations and the corresponding perturbative coefficient at the leading order. The latter calculation is performed by adopting the zeta-function resummation techniques. We make a benchmark test of our scheme in quenched QCD with the plaquette gauge action. The running of the coupling constant is determined by applying the step scaling procedure. Using several methods to improve the statistical accuracy, we show that the running coupling constant can be determined in a wide range of energy scales with relatively small number of gauge configurations.
Date: January 1, 2009
Creator: Kurachi, Masafumi; Bilgici, Erek; Flachi, Antonion; Itou, Etsuko; David Lin, C J; Matsufuru, Hideo et al.
Partner: UNT Libraries Government Documents Department

Topological excitations and second order transitions in 3D O(N) models

Description: I discuss several examples of critical phenomena in O(N) models where topological excitations play an important role at criticality. I focus particular attention on the O(2) model in 3D, where recent measurements of the vortex string length distribution in equilibrium suggest the existence of a quantitative picture of the critical behavior in terms of defects. The compatibility of this perspective with renormalization group predictions is examined.
Date: January 1, 2001
Creator: Bettencourt, L. (Luis M. A.)
Partner: UNT Libraries Government Documents Department

Scaling behavior of improvement and renormalization constants.

Description: This talk summarizes results for all the scale independent renormalization constants for bilinear currents ( Z A, ZV, and Zs/Zp), the improvement constants (CA, CV, and CT), the quark mass dependence of 20, and the coefficients of the equation of motion operators for O(a) improved lattice QCD. Using data at p = 6.0, 6.2 and 6.4 we study the scaling behavior of these quantities and quantify residual discretization errors.
Date: January 1, 2001
Creator: Bhattacharya, T. (Tanmoy); Gupta, R. (Rajan); Lee, W. (Weonjong) & Sharpe, S. R. (Stephen R.)
Partner: UNT Libraries Government Documents Department

Effective description of brane terms in extra dimensions

Description: We study how theories defined in (extra-dimensional) spaces with localized defects can be described perturbatively by effective field theories in which the width of the defects vanishes. These effective theories must incorporate a ''classical'' renormalization, and we propose a renormalization prescription a la dimensional regularization for codimension 1, which can be easily used in phenomenological applications. As a check of the validity of this setting, we compare some general predictions of the renormalized effective theory with those obtained in a particular ultraviolet completion based on deconstruction.
Date: January 1, 2006
Creator: del Aguila, Francisco; Perez-Victoria, Manuel & Santiago, Jose
Partner: UNT Libraries Government Documents Department

Elements of fractal generalization of dual-porosity model for solute transport in unsaturated fractured rocks

Description: In this study, new elements were developed to generalize the dual-porosity model for moisture infiltration on and solute transport in unsaturated rocks, taking into account fractal aspects of the percolation process. Random advection was considered as a basic mechanism of solute transport in self-similar fracture systems. In addition to spatial variations in the infiltration velocity field, temporal fluctuations were also taken into account. The rock matrix, a low-permeability component of the heterogeneous geologic medium, acts as a trap for solute particles and moisture. Scaling relations were derived for the moisture infiltration flux, the velocity correlation length, the average velocity of infiltration, and the velocity correlation function. The effect of temporal variations in precipitation intensity on the infiltration processes was analyzed. It showed that the mode of solute transport is determined by the power exponent in the advection velocity correlation function and the dimensionality of the trapping system, both of which may change with time. Therefore, depending on time, various transport regimes may be realized: superdiffusion, subdiffusion, or classical diffusion. The complex structure of breakthrough curves from changes in the transport regimes was also examined. A renormalization of the solute source strength due to characteristic fluctuations of highly disordered media was established.
Date: September 1, 2008
Creator: Bolshov, L.; Kondratenko, P.; Matveev, L. & Pruess, K.
Partner: UNT Libraries Government Documents Department

Behavior of the finite-sized, three-dimensional, Ising model near the critical point

Description: Recent work showing the validity of hyperscaling involved results for finite size systems very near the critical point. The authors study this problem in more detail, and give estimators related to the Binder cumulant ratio which seem to approach the critical temperature from above and below. Based on these results, they estimate that the renormalized coupling constant, computed for the temperature fixed at the critical temperature and then taking the large system-size limit, is about 4.9 {+-} 0.1, and give a likely lower bound for it of 4.5. These estimates are argued to suffice to show the validity of hyperscaling.
Date: May 1, 1996
Creator: Baker, G.A. Jr. & Gupta, R.
Partner: UNT Libraries Government Documents Department

Physics of the 1 Teraflop RIKEN-BNL-Columbia QCD project. Proceedings of RIKEN BNL Research Center workshop: Volume 13

Description: A workshop was held at the RIKEN-BNL Research Center on October 16, 1998, as part of the first anniversary celebration for the center. This meeting brought together the physicists from RIKEN-BNL, BNL and Columbia who are using the QCDSP (Quantum Chromodynamics on Digital Signal Processors) computer at the RIKEN-BNL Research Center for studies of QCD. Many of the talks in the workshop were devoted to domain wall fermions, a discretization of the continuum description of fermions which preserves the global symmetries of the continuum, even at finite lattice spacing. This formulation has been the subject of analytic investigation for some time and has reached the stage where large-scale simulations in QCD seem very promising. With the computational power available from the QCDSP computers, scientists are looking forward to an exciting time for numerical simulations of QCD.
Date: October 16, 1998
Partner: UNT Libraries Government Documents Department

Nonperturbative renormalization of QED in light-cone quantization

Description: As a precursor to work on QCD, we study the dressed electron in QED non-perturbatively. The calculational scheme uses an invariant mass cutoff, discretized light cone quantization, a Tamm-Dancoff truncation of the Fock space, and a small photon mass. Nonperturbative renormalization of the coupling and electron mass is developed.
Date: August 1, 1996
Creator: Hiller, J.R. & Brodsky, S.J.
Partner: UNT Libraries Government Documents Department

Maximal neutrino mixing from a minimal flavor symmetry

Description: The authors study a number of models, based on a non-Abelian discrete group, that successfully reproduce the simple and predictive Yukawa textures usually associated with U(2) theories of flavor. These models allow for solutions to the solar and atmospheric neutrino problems that do not require altering successful predictions for the charged fermions or introducing sterile neutrinos. Although Yukawa matrices are hierarchical in the models they consider, the mixing between second- and third-generation neutrinos is naturally large. They first present a quantitative analysis of a minimal model proposed in earlier work, consisting of a global fit to fermion masses and mixing angles, including the most important renormalization group effects. They then propose two new variant models: The first reproduces all important features of the SU(5) x U(2) unified theory with neither SU(5) nor U(2). The second demonstrates that discrete subgroups of SU(2) can be used in constructing viable supersymmetric theories of flavor without scalar universality even though SU(2) by itself cannot.
Date: February 1, 2000
Creator: Aranda, A.; Carone, C.D. & Lebed, R.F.
Partner: UNT Libraries Government Documents Department