arXiv subjects
Publications and source records attributed to Alok Kumar.
We consider Gribov's equation for inverse quark Green function with and without pion correction. With polar parametrization of inverse quark Green function, we relate the dynamical mass function without pion correction, $M_{0}(q^2)$ and with pion correction, $M(q^2)$ at low momentum. A graph is plotted for $M(q^2)$ and $M_{0}(q^2)$ with q for low momentum. It is found that at low momenta pion corrections are small.
We construct a minimal example of a supersymmetric grand unified model in a toroidal compactification of type I string theory with magnetized D9-branes. All geometric moduli are stabilized in terms of the background internal magnetic fluxes which are of "oblique" type (mutually non-commuting). The gauge symmetry is just SU(5) and the gauge non-singlet chiral spectrum contains only three families of quarks and leptons transforming in the $10+{\bar 5}$ representations.
The one-loop effective energy density of a pure SU(2) Yang-Mills theory in the Savvidy background, at finite temperature and chemical potential is examined with emphasis on the unstable modes. After identifying the stable and unstable modes, the stable modes are treated in the quadratic approximation. For the unstable modes, the full expansion including the cubic and the quartic terms in the fluctuations is used. The functional integrals for the unstable modes are evaluated and added to the results for the stable modes. The resulting energy density is found to be {\it{real}}, coinciding with the real part of the energy density in the quadratic approximation of earlier study. There is now {\it{no imaginary part.}} Numerical results are presented for the variation of the energy density with temperature for various choices of the chemical potential.
We study stabilization of moduli in the type--IIB superstring theory on the six-dimensional toroidal orientifold $\T^6/Ω\cdot(-1)^{F_L}\cdot\Z_2$. We consider background space-filling D9-branes wrapped on the orientifold along with non-Abelian fluxes on its world-volume and demonstrate with two examples that this can stabilize all the complex structure moduli and some of the Kähler moduli.
In this paper, we present several gravitational wave solutions in AdS_5 X S^5 string backgrounds, as well as in AdS_7 X S^4 and AdS_4 X S^7 backgrounds in M-theory, generalizing the results of hep-th/0403253 by one of the authors. In each case, we present the general form of such solutions and give explicit examples, preserving certain amount of supersymmetry, by taking limits on known BPS D3 and M2, M5-brane solutions in pp-wave backgrounds. A key feature of our examples is the possibility of a wider variety of wave profiles, than in pure gravity and string/M-theory examples known earlier, coming from the presence of various p-form field strengths appearing in the gravitational wave structure.
The Dual Meissner Effect description of QCD in the confining region provides $\frac{1}{q^4}$ behaviour for the gluon propagator and involves the dual gluon mass $m$ as a parameter. This is used in the Schwinger-Dyson equation for the quarks in the infrared region to exhibit chiral symmetry breaking for light quarks. Using the light quark condensate as input, the dual gluon mass is determined and its importance in showing the asymptotic free behaviour of the extrinsic curvature coupling in the rigid QCD string is discussed.
Inspired by the studies of gravitational waves in anti-de Sitter universe, in general relativity, in this paper we investigate the possibility of similar solutions in IIB string theory on $AdS_3 x S^3 x R^4$. We give a general form for such solutions in this background and present several explicit examples, by directly solving the field equations, as well as the ones obtained by taking a scaling limit on D1-D5 brane systems in a pp-wave background. The form of the metric in our solutions corresponds to a gravitational wave in $AdS_3$. We show the supersymmetric nature of these solutions and discuss the possibility of their generalizations to other anti-de Sitter backgrounds, including the ones in four dimensions.
The classical action of a two dimensional N=2 supersymmetric theory, characterized by a general Kähler potential, is written down on a non(anti)commutative superspace. The action has a power series expansion in terms of the determinant of the non(anti)commutativity parameter $C^{αβ}$. The theory is explicitly shown to preserve half of the N=2 supersymmetry, to all orders in (det C)^n. The results are further generalized to include arbitrary superpotentials as well.
The cubic interaction vertex and the dynamical supercharges are constructed for open strings ending on D7-branes, in light-cone superstring field theory in PP-wave background. In this context, we write down the symmetry generators in terms of the relevant group structure: SU(2) x SU(2) x SO(2) x SO(2), originating from the eight transverse directions in the PP-wave background and use the expressions to explicitly construct the vertex at the level of stringy zero modes. The results are further generalized to include all the stringy excitations as well.
We study the Penrose limit of ODp theory. There are two different PP-wave limits of the theory. One of them is a ten dimensional PP-wave and the other a four dimensional one. We observe the later one leads to an exactly solvable background for type II string theories where we have both NS and RR fields. The Penrose limit of different branes of string (M-theory) in a nonzero B/E field (C field) is also studied. These backgrounds are conjectured to provide dual description of NCSYM, NCOS and OM theory. We see that under S-duality the subsector of NCSYM$_4$ and NCOS$_4$ which are dual to the corresponding string theory on PP-wave coming from NCYM$_4$ and NCOS$_4$ map to each other for given null geodesic.
We present several supergravity solutions corresponding to both Dp, as well as Dp-Dp' systems, in NS-NS and R-R PP-wave background originating from AdS_3 times S^3 times R^4. The Dp brane solutions, p=1,..,5 are fully localized, whereas Dp-Dp' are localized along common transverse directions. We also discuss the supersymmetry properties of these solutions and the worldsheet construction for the p-p' system.
We present a class of static membrane solutions, with non-flat worldvolume geometry, in the eleven dimensional supergravity with source terms. This class of solutions contains supersymmetric as well as a large class of non-supersymmetric configurations. We comment about near horizon limit and stability of these solutions and point out an interesting relation with certain two dimensional dilaton gravity system.
We use recently proposed translations isometries of pp-waves to construct D4 and D3 brane solutions, using T-duality transformations, in exactly solvable pp-wave background originating from $AdS_3\times S^3$ geometry. A unique property of the new brane solutions is the breaking of SO(10-p-1) symmetry in the transverse direction of the branes due to the presence of constant NS-NS and R-R background fluxes. We verify that the our `localized' solutions satisfy the field equations and explicitly present the corresponding Killing spinors. We also show the connection of our results to certain M5-branes in pp-wave geometry.
We present classical solutions for a D5 and NS5-branes in a pp-wave background. The worldvolume coordinates for these branes lie along a six dimensional pp-wave configuration obtained from $AdS_3 \times S_3$ in a Penrose limit. One in addition has nontrivial R-R 3-form field strength as well as a dilaton background. Classical solutions for Dp-branes (p> 5), as well as their bound states, are then generated in both IIA and IIB string theories by using T-duality symmetries. We also briefly discuss the construction of Dp-branes in pp-wave backgrounds, obtained from string theories on $AdS_m\times S^m$. Finally, the construction of the above D5-brane solution is presented from the point of view of the Green-Schwarz worldsheet string theory and its low lying spectrum is discussed.
We construct new D-brane bound states using charged macroscopic type IIB string solutions.A generic bound state solution, when dimensionally reduced, carries multiple gauge charges. Starting with D=9 charged macroscopic strings, we obtain solutions in D=10, which are interpreted as carrying (F, D0, D2) charges as well as nonzero momenta. The masses and charges are also explicitly shown to satisfy the non-threshold bound of 1/2 BPS objects. Our solutions reduce to the known D-brane bound state solutions with appropriate restrictions in the parameter space. We further generalize the results to (Dp- D(p+2)) bound state in IIA/B theories, giving an explicit example with p=1.
We show the existence of non-threshold bound states of (p, q) string networks and D3-branes, preserving 1/4 of the full type IIB supersymmetry, interpreted as string networks dissolved in D3-branes. We also write down the expression for the mass density of the system and discuss the extension of the construction to other Dp-branes. Differences in our construction of string networks with the ones interpreted as dyons in N=4 gauge theories are also pointed out.
We consider quantization of open string theories in linear dilaton and constant antisymmetric tensor backgrounds and discuss the noncommutativity of space-time coordinates arising in such theories, including their relationship with light-like noncommutativity as well as backgrounds with null isometries. It is argued that the results can also be understood using space-time equations of motion of the string modes. We then present N= 2 supersymmetric generalization of these theories and the associated noncommutativity structure.
We analyze open and mixed sector tree-level amplitudes of N=2 strings in a space-time with (2,2) signature, in the presence of constant B field. The expected topological nature of string amplitudes in the open sector is shown to impose nontrivial constraints on the corresponding noncommutative field theory. In the mixed sector, we first compute a 3-point function and show that the corresponding field theory is written in terms of a generalized *-product. We also analyze a 4-point function (A_{oooc}) of the mixed sector in Theta ---> infinity limit.