String Description Research Articles

On type IIA Penrose limit and 𝒩 = 6 Chern-Simons theories

Recently, Aharony, Bergman, Jafferis and Maldacena proposed that the N=6 Chern-Simons gauge theories are holographically dual to the M-theory backgrounds with multiple M2-branes on orbifolds C^4/Z_k. When k is large, they have the type IIA string description. In this paper we analyze the Penrose limit of this IIA background and express the string spectrum as the conformal dimensions of operators in the gauge theories. For BPS operators, we can confirm the agreements between the IIA string on plane waves and the gauge theories. We point out that there exist BMN-like operators in the gauge theories, though their holographic interpretation does not seem to be simple. Also we analyze the weak coupling limit of this theory and show that the Hagedorn/deconfinement transition occurs as expected.

Embedding nonlinear [formula omitted] sigma model into [formula omitted] super-Yang–Mills theory

Anomalous dimensions of high-twist Wilson operators have a nontrivial scaling behavior in the limit when their Lorentz spin grows exponentially with the twist. To describe the corresponding scaling function in planar N = 4 SYM theory, we analyze an integral equation recently proposed by Freyhult, Rej and Staudacher and argue that at strong coupling it can be casted into a form identical to the thermodynamical Bethe Ansatz equations for the nonlinear O ( 6 ) sigma model. This result is in a perfect agreement with the proposal put forward by Alday and Maldacena within the dual string description, that the scaling function should coincide with the energy density of the nonlinear O ( 6 ) sigma model embedded into AdS 5 × S 5 .

Quark-gluon plasma/black hole duality from gauge/gravity correspondence

The Quark-Gluon Plasma (QGP) is the QCD phase of matter expected to be formed at small proper-times in the collision of heavy-ions at high energy. Experimental observations seem to favor a strongly coupled QCD plasma with the hydrodynamic properties of a quasi-perfect fluid, i.e. rapid thermalization (or isotropization) and small viscosity. The theoretical investigation of such properties is not obvious, due to the the strong coupling. The Gauge/Gravity correspondence provides a stimulating framework to explore the strong coupling regime of gauge theories using the dual string description. After a brief introduction to Gauge/Gravity duality, and among various existing studies, we focus on challenging problems of QGP hydrodynamics, such as viscosity and thermalization, in terms of gravitational duals of both the static and relativistically evolving plasma. We show how a Black Hole geometry arises naturally from the dual properties of a nearly perfect fluid and explore the lessons and prospects one may draw for actual heavy ion collisions from the Gauge/Gravity duality approach.

G2 Hitchin functionals at one loop

We consider the quantization of the effective target space description of topological M-theory in terms of the Hitchin functional whose critical points describe seven manifolds with a G2 structure. The one-loop partition function for this theory is calculated and an extended version of it, that is related to the generalized G2 geometry, is compared with the topological G2 string. We relate the reduction of the effective action for the extended G2 theory to the Hitchin functional description of the topological string in six dimensions. The dependence of the partition functions on the choice of background G2 metric is also determined.

Probing the ground state in gauge theories

We consider two very different models of the flux tube linking two heavy quarks: a string linking the matter fields and a Coulombic description of two separately gauge invariant charges. We compare how close they are to the unknown true ground state in compact U(1) and the SU(2) Higgs model. Simulations in compact U(1) show that the string description is better in the confined phase but the Coulombic description is best in the deconfined phase; the last result is shown to agree with analytical calculations. Surprisingly in the nonabelian theory the Coulombic description is better in both the Higgs and confined phases. This indicates a significant difference in the width of the flux tubes in the two theories.

A semiclassical string description of Wilson loop with local operators

We discuss a semiclassical string description to circular Wilson loops without/with local operator insertions. Type IIB string theory on AdS 5 × S 5 is expanded around the corresponding classical solutions with respect to fluctuations and semiclassical quadratic actions are computed. Then the dual corresponding operators describing the fluctuations are discussed from the point of view of a small deformation of the Wilson loops. The result gives new evidence for AdS/CFT correspondence.

Consistency conditions in the chiral ring of super-Yang–Mills theories

Starting from the generalized Konishi anomaly equations at the non-perturbative level, we demonstrate that the algebraic consistency of the quantum chiral ring of the N = 1 super-Yang–Mills theory with gauge group U ( N ) , one adjoint chiral superfield X and N f ⩽ 2 N flavours of quarks implies that the periods of the meromorphic one-form Tr d z z − X must be quantized. This shows in particular that identities in the open string description of the theory, that follow from the fact that gauge invariant observables are expressed in terms of gauge variant building blocks, are mapped onto non-trivial dynamical equations in the closed string description.

Deep inelastic scattering at strong coupling from gauge/string duality: the saturation line

For gauge theories which admit a dual string description, we analyze deep inelastic scattering at strong 't Hooft coupling and high energy, in the vicinity of the unitarity limit. We discuss the onset of unitarity corrections and determine the saturation line which separates weak scattering from strong scattering in the parameter space of rapidity and photon virtuality. We discover that the approach towards unitarity proceeds through two different mechanisms, depending upon the photon virtuality Q^2 : single Pomeron exchange at relatively low Q^2 and, respectively, multiple graviton exchanges at higher Q^2. This implies that the total cross-section at high energy and large Q^2 is dominated by diffractive processes. This is furthermore suggestive of a partonic description where all the partons have transverse momenta below the saturation momentum and occupation numbers of order one.

The string/gauge theory correspondence in QCD

Ideas about a duality between gauge fields and strings have been around for many decades. During the last ten years, these ideas have taken a much more concrete mathematical form. String descriptions of the strongly coupled dynamics of semi-realistic gauge theories, exhibiting confinement and chiral symmetry breaking, are now available. These provide remarkably simple ways to compute properties of the strongly coupled quark-gluon fluid phase, and also shed new light on various phenomenological models of hadron fragmentation. We present a review and highlight some exciting recent developments.

Chiral symmetry and the string description of excited hadrons

A large symmetry group is perhaps experimentally observed in excited hadrons which includes the chiral group $U(2{)}_{L}\ifmmode\times\else\texttimes\fi{}U(2{)}_{R}$ as a subgroup. To possess this large symmetry a dynamical model for excited hadrons, presumably a string model, should explain formation of chiral multiplets and, at the same time, predict coinciding slopes of the angular and radial Regge trajectories. This is possible only if both the dynamics of the string and the chirality of the quarks at the ends of the string are considered together. We construct a model-independent unitary transformation from the relativistic chiral basis to the ${^{2S+1}L_{J}}$ basis, commonly used in hadronic phenomenology as well as in the string models, and demonstrate that a hadron belonging to the given chiral representation is a fixed superposition of the basis vectors with different $L$'s. Thus the description of highly excited hadron in terms of a fixed $L$ is not compatible with chiral symmetry and has to be disregarded in favor of the description in terms of the total hadron spin $J$. Therefore, dynamics of the string must deliver the principal quantum number $\ensuremath{\sim}n+J$, in order chiral multiplets with different spins to become degenerate, as required by the large symmetry group.

Dirac Formulation of Free Open String

Dirac formulation of open relativistic strings as systems with constraints is made explicitly. Classical theory is given in the standard light-cone and covariant center-of-mass gauges. It is mentioned that the well-known result D = 26 is affected by using the standard quantization of the mutually independent nonphysical boson creation and annihilation operators. It is shown that in the Dirac formulation these operators are not independent in both the gauges. Concepts of Physics, Vol. IV, No. 4 (2007) DOI: 10.2478/v10005-007-0023-x 487 We give some new conditions on these operators and show that the theory is consistent with Poincare algebra in any dimension D. 488 Concepts of Physics, Vol. IV, No. 4 (2007) Dirac Formulation of Free Open String 1 Hamilton description of classical open string We will study the Nambu–Goto [1] free open string in dimension D. We assume the sign convention gμν = diag(−1, 1, . . . , 1), where μ, ν = 0, 1, . . . , D − 1. The string is described by the functions X(τ, σ), where τ ∈ R and σ ∈ 〈0, π〉. The classical string is described by Lagrangian L(X) = −ω ∫ π 0 Ldσ, where ω > 0 is a constant and the Lagrangian density L(τ, σ) is L = √( ẊX ′ )2 − (Ẋ)2(X ′)2 . A dot means partial derivation with respect to τ , a dash with respect to σ, and XY = gμνXY ν = XμY ν . The boundary conditions are X ′ μ(τ, 0) = X ′ μ(τ, π) = 0. In the Hamiltonian formulation we define momenta Pμ(τ, σ) = δL δẊμ(σ) = ω Ẋμ(X ′X ′)−X ′ μ(ẊX ′) √( ẊX ′ )2 − (Ẋ)2(X ′)2 . (1) From (1) we obtain the relations Φ1 = 1 2 ( P 2 + ω ( X ′ )2) = 0 , Φ2 = PX ′ = 0 (2) called constraints. For the Poisson brackets of two functionals F (X,P ) and G(X,P ) we have { F,G } = ∫ π 0 ( δF δXμ(σ) δG δPμ(σ) − δF δPμ(σ) δG δXμ(σ) ) dσ . (3) In particular, the relation { X(σ), P ν(σ′) } = gδ(σ − σ′) is valid. The Hamiltonian of the system with constraints (2) is

Models with quartic potential of dynamical SUSY breaking in meta-stable vacua

We search for models of dynamical SUSY breaking in meta-stable vacua which might have dual string descriptions with a few brane probes. Two models with quartic superpotential are proposed: One of them might be closely related to the dual gauge theory to the flavored Maldacena-Nunez geometry by Casero, Nunez, and Paredes with a few additional brane probes corresponding to massive flavors. The other model might be dual to the Klebanov-Strassler geometry with one fractional D3-brane and a few D7-branes as probes.

Black string entropy and Fourier-Mukai transform

We propose a microscopic description of black strings in F-theory based on string duality and Fourier-Mukai transform. These strings admit several different microscopic descriptions involving D-brane as well as M2 or M5-brane configurations on elliptically fibered Calabi-Yau threefolds. In particular our results can also be interpreted as an asymptotic microstate count for D6-D2-D0 configurations in the limit of large D2-charge on the elliptic fiber. The leading behavior of the microstate degeneracy in this limit is shown to agree with the macroscopic entropy formula derived from the black string supergravity solution.

Dual string description of Wilson loop in non-commutative gauge theory

The Wilson loop in some non-commutative gauge theories is studied by using the dual string description in which the corresponding string is on the curved background with B field. For the theory in which a constant B field is turned on along the brane worldvolume the Wilson loop always shows a Coulomb phase, as studied in the previous literature. We extend the examination to the theory with a non-constant B field, which duals to the gauge theory with non-constant non-commutativity, and re-examine the theory in the presence of a nonzero B field with one leg along the brane worldvolume and other transverse to it, which duals to a non-commutative dipole theory. The expectation value of the Wilson loop is calculated to the lowest order by evaluating the area of the string worldsheet. The results show that, while the non-commutativity could modify the Coulomb type potential in IR it may produce a strong repulsive force between the quark and anti-quark if they are close enough. In particular, we find that there presents a minimum distance between the quarks and that the distance is proportional to the value of the non-commutativity, exhibiting the nature of the non-commutative theory.

Giant magnons

Studies of ${\cal N}=4$ super Yang Mills operators with large R-charge have shown that, in the planar limit, the problem of computing their dimensions can be viewed as a certain spin chain. These spin chains have fundamental ``magnon'' excitations which obey a dispersion relation that is periodic in the momentum of the magnons. This result for the dispersion relation was also shown to hold at arbitrary 't Hooft coupling. Here we identify these magnons on the string theory side and we show how to reconcile a periodic dispersion relation with the continuum worldsheet description. The crucial idea is that the momentum is interpreted in the string theory side as a certain geometrical angle. We use these results to compute the energy of a spinning string. We also show that the symmetries that determine the dispersion relation and that constrain the S-matrix are the same in the gauge theory and the string theory. We compute the overall S-matrix at large 't Hooft coupling using the string description and we find that it agrees with an earlier conjecture. We also find an infinite number of two magnon bound states at strong coupling, while at weak coupling this number is finite.

Light meson spectrum and classical symmetries of QCD

Modern spectroscopic data on the light non-strange meson spectrum is analyzed. It is argued that the observed regularities of the experimental spectrum for highly excited states favour a partial restoration of all approximate classical symmetries of a QCD Lagrangian (conformal, chiral and axial) broken by quantum corrections. The rate of restoration of classical symmetries is estimated. The dependence of the resonance widths on the corresponding masses is systematically checked. On average, it turns out to be universal for high excitations as predicted by the effective string description.

Anti-hemostatic Effects of a Serpin from the Saliva of the Tick Ixodes ricinus

Serpins (serine protease inhibitors) are a large family of structurally related proteins found in a wide variety of organisms, including hematophagous arthropods. Protein analyses revealed that Iris, previously described as an immunomodulator secreted in the tick saliva, is related to the leukocyte elastase inhibitor and possesses serpin motifs, including the reactive center loop (RCL), which is involved in the interaction between serpins and serine proteases. Only serine proteases were inhibited by purified recombinant Iris (rIris), whereas mutants L339A and A332P were found devoid of any protease inhibitory activity. The highest Ka was observed with human leukocyte-elastase, suggesting that elastase-like proteases are the natural targets of Iris. In addition, mutation M340R completely changed both Iris substrate specificity and affinity. This likely identified Met-340 as amino acid P1 in the RCL. The effects of rIris and its mutants were also tested on primary hemostasis, blood clotting, and fibrinolysis. rIris increased platelet adhesion, the contact phase-activated pathway of coagulation, and fibrinolysis times in a dose-dependent manner, whereas rIris mutant L339A affected only platelet adhesion. Taken together, these results indicate that Iris disrupts coagulation and fibrinolysis via the anti-proteolytic RCL domain. One or more other domains could be responsible for primary hemostasis inhibition. To our knowledge, this is the first ectoparasite serpin that interferes with both hemostasis and the immune response.

LargeNreductions and holography

The large $N$ reductions in gauge theories are identified with dimensional reductions with homogeneous distribution of the eigenvalues of the gauge fields, and it is used to identify the corresponding closed string descriptions in the Maldacena duality. When one does not take the zero-radii limit, the large $N$ reductions are naturally extended to the equivalences between the gauge theories and the ``generalized'' reduced models, which naturally contain the notion of $T$-dual equivalence. In the dual gravitational description, $T$-duality relates two type IIB supergravity solutions, the near horizon geometry of $D3$-branes, and the near horizon geometry of $D$-instantons distributed densely and homogeneously on the dual torus. This is the holographic description of the generalized large $N$ reductions.

Computing Wilson lines with dielectric branes

Wilson lines in N = 4 SYM can be computed in terms of branes carrying electric flux, i.e. F-strings dissolved in their worldvolumes. It is then natural to think that those configurations are the effective description of strings expanding due to dielectric effect to D-branes. In this note we explicitly show this for a class of such configurations, namely those dual to Wilson lines either in the symmetric or in the antisymmetric tensor product of fundamentals.

CHIRAL DYNAMICS FROM THE HADRONIC STRING: GENERAL FORMALISM

Quantum Chromodynamics (QCD) at long distances can be described by the chiral Lagrangian. On the other hand there is overwhelming evidence that QCD and all non-Abelian theories admit an effective string description. Here we review a derivation of the (intrinsic) parity-even chiral Lagrangian by requiring that the propagation of the QCD string takes place on a background where chiral symmetry is spontaneously broken. Requiring conformal invariance leads to the equation of motion of the chiral Lagrangian. We then proceed to coupling the string degrees of freedom to external gauge fields and we recover in this way the covariant equations of motion of the gauge-invariant chiral Lagrangian at [Formula: see text]. We consider next the parity-odd part (Wess–Zumino–Witten) action and argue that this requires the introduction of the spin degrees of freedom (absent in the usual effective action treatment). We manage to reproduce the Wess–Zumino–Witten term in two dimensions (2D) in an unambiguous way. In 4D the situation is considerably more involved. We outline the modification of boundary interaction that is necessary to induce the parity-odd part of the chiral Lagrangian.