String Probes Research Articles

MODELING M-THEORY VACUA VIA GAUGED S-DUALITY

We construct a model of M-theory vacua using gauged S-duality and the Chan–Paton symmetries by introducing an infinite number of open string charges. In the Bechi–Rouet–Stora–Tyutin formalism, the local description of the gauged S-duality on its moduli space of vacua is fully determined by one physical state condition on the vacua. We introduce the string probe of the spatial degrees of freedom and define the increment of the cosmic time. The dimensionality of space–time and the gauge group of the low energy effective theory originate in the symmetries (with or without their breakdown) in our model. This modeling leads to the derived category formulation of the quantum mechanical world including gravity and to the concept of a nonlinear potential of gauged and affinized S-duality which specifies the morphism structure of this derived category.

Radio jets and galaxies as cosmic string probes

The lensing effect of a cosmic string is studied, and some new methods are proposed to detect the cosmic string. The technique for using jets as extended gravitational lensing probes was firstly explored by Kronberg. We use the "alignment-breaking parameter" $ \eta_G $ as a sensitive indicator of gravitational distortion by a wiggly cosmic string. Then, we applied the non-constant deflection angle to jets, and $ \eta_G $ of a specific jet is just related to the projected slope of the jet. At least three jets in the sample of Square Kilometer Array (SKA) would have significant signals ($ \eta_G >10^\circ $) if the wiggly infinite cosmic string existed. The distortion of elliptical object is also studied and used to do a statistical research on directions of axes and ellipticities of galaxies. In the direction of the string, we find that galaxies appear to be more elliptical for an observer and the distribution of apparent ellipticity changes correspondingly. Ellipticity distribution of current SDSS spiral sample has the signal-to-noise ratio up to 8.48 which is large enough for astronomical observations. The future survey, such as Large Synoptic Survey Telescope (LSST) and Dark Energy Survey (DES), would weaken the requirement of special geometry in the data processing. As a result, all kinds of distributions, including ellipticity axis distribution, would serve as probes to detect wiggly strings in the near future. In brief, if a wiggly cosmic string existed, these signals would be convenient to be observed with the future weak lensing survey or other surveys in deep space. If there was no lensing signal in these distributions, it would give the upper limit of the abundance of infinite strings.

String in Hořava-Lifshitz gravity

We generalize recent analysis of the dynamics of point particle in Horava-Lifshitz background to the case of string probe when we replace the Hamiltonian constraint of the Polyakov string with the constraint that breaks Lorentz invariance of target space-time. Then we find corresponding Lagrangian and argue that the world-sheet theory is invariant under foliation preserving diffeomorphism. Finally we discuss the Hamiltonian dynamics and show that this is well defined on condition that the world-sheet lapse function obeys the projectability condition.

Drag force in a hot non-relativistic, non-commutative Yang-Mills plasma

We apply the standard technique of Null Melvin Twist to the non-extremal (D1, D3) bound state configuration of type IIB string theory. Under a particular decoupling limit, such configuration represents the gravity dual of the non-relativistic, non-commutative Yang-Mills theory at a finite temperature. We then use the AdS/CFT and the string probe approach to compute the drag force on an external quark moving through such a hot non-relativistic, non-commutative YM plasma. We discuss various limiting cases to show the interplay between the non-relativistic as well as the non-commutative effect of the general drag force expression.

Wilson loops in string duals of walking and flavored systems

We consider the VEV of Wilson loop operators by studying the behavior of string probes in solutions of Type IIB string theory generated by Nc D5 branes wrapped on an internal manifold. In particular, we focus on solutions to the background equations that are dual to field theories with a walking gauge coupling as well as for flavored systems. We present in detail our walking solution and emphasize various general aspects of the procedure to study Wilson loops using string duals. We discuss the special features that the strings show when probing the region associated with the walking of the field theory coupling.

Holography and drag force in thermal plasma of non-commutative Yang–Mills theories in diverse dimensions

We use holography and a string probe approach to compute the drag force on a quark moving in a thermal plasma of non-commutative Yang–Mills (NCYM) theories in various dimensions. The gravity background in these cases are described by a particular decoupling limit of non-extremal (D(p−2),Dp)-brane bound state system. We show how the drag force on an external quark moving in the dual NCYM theories gets corrected due to non-commutativity and as a result the effective viscosity of the plasma gets reduced. We have obtained the drag force for both small and large non-commutativity. This was known earlier for (3+1)-dimensional NCYM theory, however, we find that the corrections for the general case typically depend on the dimensionality of the NCYM theories, indicating that the structure of the drag force is non-universal.

Semi-classical probe strings on giant gravitons backgrounds

In the first part of this paper we study two $Z_2$ symmetries of the LLM metric, both of which exchange black and white regions. One of them which can be interpreted as the particle-hole symmetry is the symmetry of the whole supergravity solution while the second one is just the symmetry of the metric and changes the sign of the fivefrom flux. In the second part of the paper we use closed string probes and their semi-classical analysis to compare the two 1/2 BPS deformations of $AdS_5\times S^5$, the smooth LLM geometry which contains localized giant gravitons and the superstar case which is a solution with naked singularity corresponding to smeared giants. We discuss the realization of the $Z_2$ symmetry in the semi-classical closed string probes point of view.

PROBING THE 5TH DIMENSION WITH THE QCD STRING

A salient feature of String/Gauge duality is an extra 5th dimension. Here we study the effect of confining deformations of AdS5 and compute the spectrum of a string stretched between infinitely massive quarks and compare it with the quantum states of the QCD flux as determined by Kuti, Juge and Morningstar in lattice simulations. In the long flux tube limit the AdS string probes the metric near the IR cutoff of the 5th dimension with a spectrum approximated by a Nambu-Goto string in 4-d flat space, whereas at short distance the string moves to the UV region with a discrete spectrum for pure AdS5. We also review earlier results on glueballs states and the cross-over between hard and soft diffractive scattering that support this picture.

Dilatonic repulsons and confinement via the AdS/CFT correspondence

We study a class of dilatonic deformations of asymptotically AdS_5 X S^5 geometry analytically and numerically. The spacetime is non-supersymmetric and suffers from a naked singularity. We propose that the causality bound may serve as a criterion for such a geometry with a naked singularity to still make sense in the AdS/CFT correspondence. We show that the static string, the one corresponding to a large Wilson loop in the dual gauge theory, reveals confinement in a certain range of parameters of our solutions, where the singularity exhibits the repulsion that can well cloak the singularity from the static string probe. In particular, we find the exact expression for the tension of the QCD strings. We also discuss a possible interpretation of our solution in terms of unstable branes and their tachyon matter.

String Form Factors

We compute the cross section for scattering of light string probes by randomly excited closed strings. For high energy probes, the cross section factorizes and can be used to define effective form factors for the excited targets. These form factors are well defined without the need for infinite subtractions and contain information about the shape and size of typical strings. For highly excited strings the elastic form factor can be written in terms of the `plasma dispersion function', which describes charge screening in high temperature plasmas.

Closed geodesics on Gödel-type backgrounds

We consider radial oscillations of supertube probes in the Godel-type background which is U-dual to the compactified pp-wave obtained from the Penrose limit of the NS five-brane near horizon geometry. The supertube probe computation can be carried over directly to a string probe calculation on the U-dual background. The classical equations of motion are solved explicitly. In general, the probe is not restricted to travel unidirectionally through any global time coordinate. In particular, we find geodesics that close.

Supersymmetric Brane-Antibrane Systems: Matrix Model Description, Stability and Decoupling Limits

After reviewing the supertubes and super brane-antibrane systems in the context of matrix model, we look for more general higher-dimensional configurations. For D3-bar{D3}, we find a non-trivial configuration with E cdot B not equal to 0 and describe the worldvolume gauge theory. We present the string probe of D3-bar{D3} system and study the decoupling limits leading to either noncommutative Super-Yang-Mills or NCOS theories with eight supercharges.

Fractional strings in (p,q) 5-brane and quiver matrix string theory

We study the (p,q)5-brane dynamics from the viewpoint of Matrix string theory in the T-dualized ALE background. The most remarkable feature in the (p,q)5-brane is the existence of ``fractional string'', which appears as the instanton of 5-brane gauge theory. We approach to the physical aspects of fractional string by means of the two types of Matrix string probes: One of which is that given in hep-th/9710065. As the second probe we present the Matrix string theory describing the fractional string itself. We calculate the moduli space metrics in the respective cases and argue on the specific behaviors of fractional string. Especially, we show that the ``joining'' process of fractional strings can be realized as the transition from the Coulomb branch to the Higgs branch of the fractional string probe. In this argument, we emphasize the importance of some monodromies related with the theta-angle of the 5-brane gauge theory.

Measuring the size and shape of strings

We define size and shape in terms of observables, i.e. scattering amplitudes. Excited strings can be measured by scattering ground-state string probes off them. We pick an example where, classically, the ends of the string trace out a circle. Our calculation shows that the radius of the circle is proportional to the mass of the string, M, in agreement with classical expectations. However, on distance scales less than √In M, quantum fluctuations are important and a classical space-time picture becomes questionable.

Electrical impedance string probes for two-phase void and velocity measurements

An instrumentation system was developed to measure two-phase flow velocity and void fraction. The principle of operation of this system was based on the measurement of the electrical impedance of two-phase mixtures. Two-phase velocity is estimated by time-of-flight analysis of signals from two spatially separated sensors. A technique involving measurement of both the capacitance and the conductance of the mixture was used to determine void fraction and correct for the effect of liquid distribution. The string probe instrumentation proved to be durable in air/water and steam/water flows and demonstrated an ability to measure a wide range of flow velocities (1–17 m/s) and void fractions (0.25−0.99+).