Dirac-Born-Infeld Research Articles

Comparing brane inflation to WMAP

We compare the simplest realistic brane inflationary model to recent cosmological data,including Wilkinson Microwave Anisotropy Probe (WMAP) three-year cosmic microwavebackground (CMB) results, Sloan Digital Sky Survey Luminous Red Galaxies(SDSS LRG) power spectrum data and Supernovae Legacy Survey (SNLS) type1a supernovae distance measures. Here, the inflaton is simply the position of aD3-brane which is moving towards a -brane sitting at the bottom of a throat (a warped, deformed conifold) in theflux compactified bulk in type IIB string theory. The analysis includes both theusual slow-roll scenario and the Dirac–Born–Infeld scenario of slow but relativisticrolling. Requiring that the throat is inside the bulk greatly restricts the allowedparameter space. We discuss possible scenarios in which a large tensor modeand/or non-Gaussianity may emerge. Here, the properties of a large tensor modedeviate from that in the usual slow-roll scenario, providing a possible stringysignature. Overall, within the brane inflationary scenario, the cosmological data areproviding information about the properties of the compactification of the extradimensions.

Baryons in holographic QCD

We study baryons in holographic QCD with $\mathrm{D}4/\mathrm{D}8/\overline{\mathrm{D}8}$ multi-D-brane system. In holographic QCD, the baryon appears as a topologically nontrivial chiral soliton in a four-dimensional effective theory of mesons. We call this topological soliton brane-induced Skyrmion. Some review of $\mathrm{D}4/\mathrm{D}8/\overline{\mathrm{D}8}$ holographic QCD is presented from the viewpoints of recent hadron physics and QCD phenomenologies. A four-dimensional effective theory with pions and $\ensuremath{\rho}$ mesons is uniquely derived from the non-Abelian Dirac-Born-Infeld (DBI) action of D8 brane with D4 supergravity background at the leading order of large ${N}_{c}$, without small amplitude expansion of meson fields to discuss chiral solitons. For the hedgehog configuration of pion and $\ensuremath{\rho}$-meson fields, we derive the energy functional and the Euler-Lagrange equation of brane-induced Skyrmion from the meson effective action induced by holographic QCD. Performing the numerical calculation, we obtain the soliton solution and figure out the pion profile $F(r)$ and the $\ensuremath{\rho}$-meson profile $\stackrel{\texttildelow{}}{G}(r)$ of the brane-induced Skyrmion with its total energy, energy density distribution, and root-mean-square radius. These results are compared with the experimental quantities of baryons and also with the profiles of standard Skyrmion without $\ensuremath{\rho}$ mesons. We analyze interaction terms of pions and $\ensuremath{\rho}$ mesons in brane-induced Skyrmion, and find a significant $\ensuremath{\rho}$-meson component appearing in the core region of a baryon.

On the slow roll expansion for brane inflation

One possibility for identifying the inflaton in the framework of string theory isthat it is a D-brane modulus. This option involves a specific, non-canonical formof the kinetic energy—the Dirac–Born–Infeld action. This note investigates theapplicability of the slow roll approximation in inflationary models of this type.To this end the slow roll expansion of Liddle, Parsons and Barrow is derivedfor the case of the DBI action. The resulting slow roll conditions augment thestandard ones valid in the case of canonical kinetic terms. It is also shown that inDBI models inflation does not require that the potential dominate the energydensity.

Geometrical dynamics of Born–Infeld objects

We present a geometrically inspired study of the dynamics of Dp-branes. We focus on the usual non-polynomial Dirac–Born–Infeld action for the worldvolume swept out by the brane in its evolution in general background spacetimes. We emphasize the form of the resulting equations of motion which are quite simple and resemble Newton's second law, complemented with a conservation law for a worldvolume bicurrent. We take a closer look at the classical Hamiltonian analysis which is supported by the ADM framework of general relativity. The constraints and their algebra are identified as well as the geometrical role they play in phase space. In order to illustrate our results, we review the dynamics of a D1-brane immersed in a AdS3 × S3 background spacetime. We exhibit the mechanical properties of Born–Infeld objects paving the way to a consistent quantum formulation.

EVOLUTION OF THE D3-BRANE FOR DYNAMICAL EMBEDDINGS

The evolution of both the D3-brane and the transverse directions has been obtained from the Dirac–Born–Infeld (DBI) action. For the special constraint put on the transverse coordinates a family of the contracting and expanding spaces has been found.

EXACT SEIBERG–WITTEN MAP AND INDUCED GRAVITY FROM NONCOMMUTATIVITY

We find a closed form for Seiberg–Witten (SW) map between ordinary and noncommutative (NC) Dirac–Born–Infeld actions. We show that NC Maxwell action after the exact SW map can be regarded as ordinary Maxwell action coupling to a metric deformed by gauge fields. We also show that reversed procedure by inverse SW map lead to a similar interpretation in terms of induced NC geometry. This implies that noncommutativity in field theory can be interpreted as field-dependent fluctuations of spacetime geometry, which genuinely realizes an interesting idea recently observed by Rivelles.

Matrix models for D-particle dynamics and the string/black hole transition

For a generic two-dimensional 0A string background, we map the Dirac–Born–Infeld action to a matrix model. This is achieved using a canonical transformation. The action describes D0-branes in this background, while the matrix model has a potential which encodes all the information of the background geometry. We apply this formalism to specific backgrounds: for Rindler space, we obtain a matrix model with an upside-down quadratic potential, while for AdS2 space, the potential is linear. Furthermore we analyse the black hole geometry with RR flux. In particular, we show that at the Hagedorn temperature, the resulting matrix model coincides with the one for the linear dilaton background. We interpret this result as a realization of the string/black hole transition.

Tachyon dark energy models: Dynamics and constraints

We explore the dynamics of dark energy models based on a Dirac-Born-Infeld (DBI) tachyonic action, studying a range of potentials. We numerically investigate the existence of tracking behavior and determine the present-day value of the equation of state parameter and its running, which are compared with observational bounds. We find that tachyon models have quite similar phenomenology to canonical quintessence models. While some potentials can be selected amongst many possibilities and fine-tuned to give viable scenarios, there is no apparent advantage in choosing a DBI scalar field instead of a Klein-Gordon one.

Late time behaviors of an inhomogeneous rolling tachyon

We study an inhomogeneous decay of an unstable D-brane in the context of Dirac-Born-Infeld (DBI)-type effective action. We consider tachyon and electromagnetic fields with dependence of time and one spatial coordinate, and an exact solution is found under an exponentially decreasing tachyon potential, ${e}^{\ensuremath{-}|T|/\sqrt{2}}$, which is valid for the description of the late time behavior of an unstable D-brane. Though the obtained solution contains both time and spatial dependence, the corresponding momentum density vanishes over the entire spacetime region. The solution is governed by two parameters. One adjusts the distribution of energy density in the inhomogeneous direction, and the other interpolates between the homogeneous rolling tachyon and static configuration. As time evolves, the energy of the unstable D-brane is converted into the electric flux and tachyon matter.

Tachyon Condensation in Unbalanced DFormula System

The tachyon condensation is studied in asymmetric DD systems. Taking a system of two pairs of D5-D5 in type IIB superstring theory in the background of large N D5-branes, we show that one BPS D1-brane comes out after the condensation. It is also seen that the BPS D1-brane feels no force from the background D5-branes. We also show that the inclusion of the fluctuation fields gives an expected Dirac-Born-Infeld (DBI) action of the resultant D1-brane. On the other hand, in the case of one pair of D5-D5 in the same background, we show that the resultant BPS D3-brane experiences attractive force from the background D5-branes.

NON-ABELIAN BORN–INFELD THEORY WITHOUT THE SQUARE-ROOT

A non-Abelian Born–Infeld theory is presented. Its construction does not require the square-root structure that characterizes the Dirac–Born–Infeld (DBI) action. The procedure is based on an Abelian theory proposed by Schrödinger that, as he showed, is equivalent to Born–Infeld theory. Various non-Abelian generalizations are possible. We focus our attention on one of them. For it, it is shown that instantons solutions exist. Our formalism could be of interest in connection with string theory and possible extensions of well-known physical results in the usual Born–Infeld Abelian case.

Observing brane inflation

Linking the slow-roll scenario and the Dirac–Born–Infeld scenario ofultra-relativistic roll (where, thanks to the warp factor, the inflaton moves slowlyeven with an ultra-relativistic Lorentz factor), we find that the KKLMMTD3–-brane inflation is robust; that is, enoughe-folds of inflation is quite generic in the parameter space of the model. Weshow that the intermediate regime of relativistic roll can be quite interestingobservationally. Introducing appropriate inflationary parameters, we explore theparameter space and give the constraints and predictions for the cosmologicalobservables in this scenario. Among other properties, this scenario allows thesaturation of the present observational bound of either the tensor/scalar ratior (in the intermediate regime) or the non-GaussianityfNL (in the ultra-relativistic regime), but not both.

Limits on non-Gaussianities from WMAP data

We develop a method for constraining the level of non-Gaussianity of density perturbationswhen the three-point function is of the ‘equilateral’ type. Departures from Gaussianity ofthis form are produced by single field models such as ghost or Dirac–Born–Infeld inflationand in general by the presence of higher order derivative operators in the effectiveLagrangian of the inflaton. We show that the induced shape of the three-pointfunction can be very well approximated by a factorizable form, making the analysispractical. We also show that, unless one has a full sky map with uniform noise, inorder to saturate the Cramer–Rao bound for the error on the amplitude of thethree-point function, the estimator must contain a piece that is linear in the data. Weapply our technique to the WMAP data obtaining a constraint on the amplitudefNLequil of ‘equilateral’non-Gaussianity: −366 < fNLequil < 238 at 95% C.L. We also apply our technique to constrain the so-called ‘local’ shape, which is predicted forexample by the curvaton and variable decay width models. We show that the inclusion of thelinear piece in the estimator improves the constraint over those obtained by the WMAP team, to−27 < fNLlocal < 121 at 95% C.L.

COSMOLOGICAL SOLUTION FROM D-BRANE MOTION IN NS5-BRANES BACKGROUND

We study dynamics of a D3-brane propagating in the vicinity of k coincident NS5 branes. We show that when gs is small, there exists a regime in which dynamics of the D-brane is governed by Dirac–Born–Infeld action while higher order derivative in the expansion cannot be neglected. This leads to a restriction on how fast scalar field may roll. We analyze the motion of a rolling scalar field in this regime, and extend the analysis to cosmological systems obtained by coupling this type of field theory to four-dimensional gravity. It also leads to some FRW cosmologies, some of which are related to those obtained with tachyon matter.

Running non-Gaussianities in Dirac-Born-Infeld inflation

We study the non-Gaussianity in the simplest infrared model of the Dirac-Born-Infeld (DBI) inflation. We show that the non-Gaussianity in such a model is compatible with the current observational bound and is within the sensitivity of future experiments. We also discuss the scale dependence of the non-Gaussianity. In DBI inflation, such a feature can be used as a probe to the properties of the background geometry of the extra dimensions or internal space.

TACHYON DYNAMICS IN OPEN STRING THEORY

In this review we describe our current understanding of the properties of open string tachyons on an unstable D-brane or brane–antibrane system in string theory. The various string theoretic methods used for this study include techniques of two-dimensional conformal field theory, open string field theory, boundary string field theory, noncommutative solitons, etc. We also describe various attempts to understand these results using field theoretic methods. These field theory models include toy models like singular potential models and p-adic string theory, as well as more realistic version of the tachyon effective action based on Dirac–Born–Infeld type action. Finally we study closed string background produced by the "decaying" unstable D-branes, both in the critical string theory and in the two-dimensional string theory, and describe the open string completeness conjecture that emerges out of this study. According to this conjecture the quantum dynamics of an unstable D-brane system is described by an internally consistent quantum open string field theory without any need to couple the system to closed strings. Each such system can be regarded as a part of the "hologram" describing the full string theory.

Strong coupling dynamics of the Higgs branch: Rolling a Higgs by collapsing an instanton

We construct the dual supergravity description of strongly coupled, large N, eight-supercharge gauge theories with fundamental hypermultiplets at points on the mixed Coulomb–Higgs branch. With certain assumptions about unknown couplings of D-branes to supergravity, this construction gives the correct metric on the hypermultiplet (Higgs-branch) component the moduli space, which decouples from the vector multiplet (Coulomb-branch) moduli. Going beyond the geodesic approximation, we find that the dynamics of a hypermultiplet VEV rolling towards a singularity on the Higgs component of the moduli space is sensitive to the vector multiplet moduli. The dual description of the approach to the singularity involves collapsing “instantons” of a non-Abelian Dirac–Born–Infeld theory in a curved background. In general, we find a decelerating approach to the singularity, although the manner of deceleration depends on the vector multiplet moduli. Upon introducing a potential on the Higgs branch of a four-dimensional N = 2 theory coupled to gravity, this deceleration mechanism might lead to interesting inflating cosmologies analogous those studied recently by Alishahiha, Silverstein and Tong.

The supermembrane revisited

The M2-brane is studied from the perspective of superembeddings. We review the derivation of the M2-brane dynamics and the supergravity constraints from the standard superembedding constraint and we discuss explicitly the induced d = 3, N = 8 superconformal geometry on the worldvolume. We show that the gauged supermembrane, for a target space with a U(1) isometry, is the standard D2-brane in a type IIA supergravity background. In particular, the D2-brane action, complete with the Dirac–Born–Infeld term, arises from the gauged Wess–Zumino worldvolume 4-form via the brane action principle. The discussion is extended to the massive D2-brane considered as a gauged supermembrane in a massive D = 11 superspace background. Type IIA supergeometry is derived using Kaluza–Klein techniques in superspace.

Constraints on Dirac-Born-Infeld type dark energy models from varying alpha

We study the variation of the effective fine-structure constant alpha for Dirac-Born-Infeld (DBI) type dark energy models. The DBI action based on string theory naturally gives rise to a coupling between gauge fields and a scalar field responsible for accelerated expansion of the universe. This leads to the change of alpha due to a dynamical evolution of the scalar field, which can be compatible with the recently observed cosmological data around the redshift $\stackrel{\texttildelow{}}{z}\ensuremath{\lesssim}3$. We place constraints on several different DBI models including exponential, inverse power-law and rolling massive scalar potentials. We find that these models can satisfy the varying alpha constraint provided that mass scales of the potentials are fine-tuned. When we adopt the mass scales which are motivated by string theory, both exponential and inverse power-law potentials give unacceptably large change of alpha, thus ruled out from observations. On the other hand the rolling massive scalar potential is compatible with the observationally allowed variation of alpha. Therefore the information of varying alpha provides a powerful way to distinguish between a number of string-inspired DBI dark energy models.

Supersymmetric Dirac–Born–Infeld action with self-dual mass term

We introduce a Dirac–Born–Infeld action to a self-dual N = 1 supersymmetric vector multiplet in three dimensions. This action is based on the supersymmetric generalized self-duality in odd dimensions developed originally by Townsend, Pilch and van Nieuwenhuizen. Even though such a self-duality had been supposed to be very difficult to generalize to a supersymmetrically interacting system, we show that the Dirac–Born–Infeld action is actually compatible with supersymmetry and self-duality in three dimensions, even though the original self-duality receives corrections by the Dirac–Born–Infeld action. The interactions can be further generalized to arbitrary (non)polynomial interactions. As a by-product, we also show that a third-rank field strength leads to a more natural formulation of self-duality in 3D. We also show an interesting role played by the third-rank field strength leading to supersymmetry breaking, in addition to accommodating a Chern–Simons form.