Noncommutative Branes Research Articles

Gravity as a quantum effect on quantum space-time

The 3+1-dimensional Einstein-Hilbert action is obtained from the 1-loop effective action on noncommutative branes in the IIB or IKKT matrix model. The presence of compact fuzzy extra dimensions K as well as maximal supersymmetry of the model is essential. The E-H action can be interpreted as interaction of K with the space-time brane via IIB supergravity, and the effective Newton constant is determined by the Kaluza-Klein scale of K. The classical matrix model defines a pre-gravity action with 2 derivatives less than the induced E-H action, governing the cosmological regime. The perturbative physics is confined to the space-time brane, which for covariant quantum space-times includes all dof of gravity, as well as a tower of higher-spin modes. The vacuum energy of the background is given in terms of the symplectic volume form, and hence does not act as cosmological constant.

String states, loops and effective actions in noncommutative field theory and matrix models

Refining previous work by Iso, Kawai and Kitazawa, we discuss bi-local string states as a tool for loop computations in noncommutative field theory and matrix models. Defined in terms of coherent states, they exhibit the stringy features of noncommutative field theory. This leads to a closed form for the 1-loop effective action in position space, capturing the long-range non-local UV/IR mixing for scalar fields. The formalism applies to generic fuzzy spaces. The non-locality is tamed in the maximally supersymmetric IKKT or IIB model, where it gives rise to supergravity. The linearized supergravity interactions are obtained directly in position space at one loop using string states on generic noncommutative branes.

On the 1-loop effective action for the IKKT model and non-commutative branes

We study the one-loop effective action of the IKKT or IIB model on a 4-dimensional non-commutative brane background. The trace-U(1) sector is governed by non-commutativity, and leads - assuming no SUSY breaking - to a higher-derivative effective action. In contrast, the non-Abelian sector at low energies reduces to SU(n) N=4 Super-Yang-Mills on the brane, with a global SO(9,1) symmetry broken spontaneously by the background. In the Coulomb branch, we recover the leading contribution to the Dirac-Born-Infeld (DBI) action, exhibiting a S^5 \times AdS^5 bulk geometry around a stack of branes. SUSY may be broken by compact extra dimensions M^4 x K, leading to an induced gravitational action on M^4 due to the trace-U(1) sector. The one-loop effective action is UV finite on such backgrounds, and the UV/IR mixing is non-pathological.

Heat kernel expansion and induced action for the matrix model Dirac operator

We compute the quantum effective action induced by integrating out fermions in Yang-Mills matrix models on a 4-dimensional background, expanded in powers of a gauge-invariant UV cutoff. The resulting action is recast into the form of generalized matrix models, manifestly preserving the SO(D) symmetry of the bare action. This provides non-commutative (NC) analogs of the Seeley-de Witt coefficients for the emergent gravity which arises on NC branes, such as curvature terms. From the gauge theory point of view, this provides strong evidence that the non-commutative \( \mathcal{N} = 4 \) SYM has a hidden SO(10) symmetry even at the quantum level, which is spontaneously broken by the space-time background. The geometrical view proves to be very powerful, and allows to predict nontrivial loop computations in the gauge theory.

One more step toward the noncommutative brane inflation

Recently a new approach to inflation proposal has been constructed via the smeared coherent state picture of spacetime noncommutativity. Here we generalize this viewpoint to a Randall–Sundrum II braneworld scenario. This model realizes an inflationary, bouncing solution without recourse to any axillary scalar or vector fields. There is no initial singularity and the model has the potential to produce scale invariant spectrum of scalar perturbations.

Emergent gravity and noncommutative branes from Yang–Mills matrix models

The framework of emergent gravity arising from Yang–Mills matrix models is developed further, for general noncommutative branes embedded in R D . The effective metric on the brane turns out to have a universal form reminiscent of the open string metric, depending on the dynamical Poisson structure and the embedding metric in R D . A covariant form of the tree-level equations of motion is derived, and the Newtonian limit is discussed. This points to the necessity of branes in higher dimensions. The quantization is discussed qualitatively, which singles out the IKKT model as a prime candidate for a quantum theory of gravity coupled to matter. The Planck scale is then identified with the scale of N = 4 SUSY breaking. A mechanism for avoiding the cosmological constant problem is exhibited.

A note on non-commutative brane inflation

In this paper, we investigate the non-commutative KKLMMT(Kachru–Kallosh–Linde–Maldacena–McAllister–Trivedi) -brane inflation scenario in detail. Incorporation of the brane inflationscenario and the non-commutative inflation scenario can nicely explainthe large negative running of the spectral index as indicated by WMAPthree-year data and can significantly release the fine-tuning for the parameterβ. Using the WMAP three-year results (blue-tilted spectral index with large negativerunning), we explore the parameter space and give the constraints and predictionsfor the inflationary parameters and cosmological observables in this scenario.We show that this scenario predicts a quite large tensor/scalar ratio and, whatis more, a too large cosmic string tension (assuming that the string couplinggs is in its likely range from 0.1 to 1) to be compatible with the present observational bound.A more detailed analysis reveals that this model has some inconsistencies according to thefit to WMAP three-year results.

The Extended Relativity Theory in Born-Clifford Phase Spaces with a Lower and Upper Length Scales and Clifford Group Geometric Unification

We construct the Extended Relativity Theory in Born-Clifford-Phase spaces with an upper R and lower length λ scales (infrared/ultraviolet cutoff). The invariance symmetry leads naturally to the real Clifford algebra Cl (2, 6, R) and complexified Clifford Cl C (4) algebra related to Twistors. A unified theory of all Noncommutative branes in Clifford-spaces is developed based on the Moyal-Yang star product deformation quantization whose deformation parameter involves the lower/upper scale $$(\hbar \lambda / R)$$ . Previous work led us to show from first principles why the observed value of the vacuum energy density (cosmological constant) is given by a geometric mean relationship $$\rho \sim L_{\rm Planck}^{-2}R^{-2} = L_{P}^{-4} (L_{\rm Planck} / R)^{2} \sim 10^{-122}M_{\rm Planck}^4$$ , and can be obtained when the infrared scale R is set to be of the order of the present value of the Hubble radius. We proceed with an extensive review of Smith’s 8D model based on the Clifford algebra Cl (1, 7) that reproduces at low energies the physics of the Standard Model and Gravity, including the derivation of all the coupling constants, particle masses, mixing angles, ....with high precision. Geometric actions are presented like the Clifford-Space extension of Maxwell’s Electrodynamics, and Brandt’s action related to the 8D spacetime tangent-bundle involving coordinates and velocities (Finsler geometries). Finally we outline the reasons why a Clifford-Space Geometric Unification of all forces is a very reasonable avenue to consider and propose an Einstein-Hilbert type action in Clifford-Phase spaces (associated with the 8D Phase space) as a Unified Field theory action candidate that should reproduce the physics of the Standard Model plus Gravity in the low energy limit.

Isometric embeddings and noncommutative branes in homogeneous gravitational waves

We characterize the worldvolume theories on symmetric D-branes in a six-dimensional Cahen–Wallach pp-wave supported by a constant Neveu–Schwarz 3-form flux. We find a class of flat noncommutative Euclidean D3-branes analogous to branes in a constant magnetic field, as well as curved noncommutative Lorentzian D3-branes analogous to branes in an electric background. In the former case, the noncommutative field theory on the branes is constructed from first principles, related to dynamics of fuzzy spheres in the worldvolumes, and used to analyse the flat space limits of the string theory. The worldvolume theories on all other symmetric branes in the background are local field theories. The physical origins of all these theories are described through the interplay between isometric embeddings of branes in the spacetime and the Penrose–Güven limit of AdS3 × S3 with Neveu–Schwarz 3-form flux. The noncommutative field theory of a non-symmetric spacetime-filling D-brane is also constructed, giving a spatially varying but time-independent noncommutativity analogous to that of the Dolan–Nappi model.

Noncommutative models in patch cosmology

We consider several classes of noncommutative inflationary models within an extended version of patch cosmological braneworlds, starting from a maximally invariant generalization of the action for scalar and tensor perturbations to a noncommutative brane embedded in a commutative bulk. Slow-roll expressions and consistency relations for the cosmological observables are provided, both in the UV and IR region of the spectrum; the inflaton field is assumed to be either an ordinary scalar field or a Born-Infeld tachyon. The effects of noncommutativity are then analyzed in a number of ways and energy regimes.

On tachyon condensation of intersecting noncommutative branes in M(atrix) theory

The interaction between the intersecting noncommutative D-branes (or membranes) is investigated within the M(atrix) theory. We first evaluate the spectrum of the off-diagonal fluctuation and see that there is a tachyon mode, which signals the instability of the intersecting branes. We next explain in detail how the tachyon modes (which are the off-diagonal fluctuations) can be combined with the original branes (which are the diagonal elements) to become a new diagonal matrix, which then represents the new recombined configurations after the tachyon condensation. The tachyon condensation configurations of the noncommutative branes we find are different from those of the commutative cases studied in the previous literatures.

Noncommutative branes from M theory

The analysis of the worldvolume effective actions of the M-theory Kaluza-Klein monopole and 9-brane suggests that it should be possible to describe non-abelian configurations of M2-branes or M5-branes if the M2-branes are transverse to the eleventh direction and the M5-branes are wrapped on it. This is determined by the fact that the Kaluza-Klein monopole and the M9-brane are constrained to move in particular isometric spacetimes. We show that the same kind of situation is implied by the analysis of the brane descent relations in M-theory. We compute some of the non-commutative couplings of the worldvolume effective actions of these non-abelian systems of M2 and M5 branes and show that they indicate the existence of configurations corresponding to N branes expanding into a higher dimensional M-brane. The reduction to Type II brings up new descriptions of coincident D-branes at strong coupling. We show that these systems have the right non-commutative charges to describe certain expanded configurations playing a role in the framework of the AdS/CFT correspondence. Finally, we discuss the realization of non-commutative brane configurations as topological solitons in non-abelian brane-antibrane systems.

Quantum mechanics on a noncommutative brane in M(atrix) theory

We consider the quantum mechanics of a particle on a noncommutative two-sphere with the coordinates obeying an SU(2)-algebra. The momentum operator can be constructed in terms of an SU(2)× SU(2)-extension and the Heisenberg algebra recovered in the smooth manifold limit. Similar considerations apply to the more general SU( n) case.

The non-commutative brane world

We propose a new higher-dimensional mechanism to localize scalar fields as well as fermionic and gauge fields. The underlying theory is a six-dimensional non-commutative field theory where non-commutativity is allowed along two extra infinite spatial dimensions and the four-dimensional brane is provided by a scalar soliton living in the non-commutative space. Making use of the powerful correspondence between non-commutative coordinates and operators on a single particle Hilbert space, we show that the non-commutative brane world admits localized chiral fermions and it ensures the localization of massless gauge fields. It may also give rise to a variety of different low-energy spectra since the localized zero mode may come along either with a discrete tower of degenerate heavy states or with a tower of Kaluza-Klein heavy states, or it may even be the only state in the low-energy spectrum.

Supergravity couplings to noncommutative branes open Wilson lines and generalised star products

Noncommutative gauge theories can be constructed from ordinary $U(\infty)$ gauge theories in lower dimensions. Using this construction we identify the operators on noncommutative D-branes which couple to linearized supergravity backgrounds, from a knowledge of such couplings to lower dimensional D-branes with no $B$ field. These operators belong to a class of gauge invariant observables involving open Wilson lines. Assuming a DBI form of the coupling we show, to second order in the gauge potential but to all orders of the noncommutativity parameter, that our proposal agrees with the operator obtained in terms of ordinary gauge fields by considering brane actions in backgrounds and then using the Seiberg-Witten map to rewrite this in terms of noncommutative gauge fields. Our result clarify why a certain {\it commutative} but {\it non-associative} ``generalized star product'' appears both in the expansion of the open Wilson line, as well as in string amplitude computations of open string - closed string couplings. We outline how our procedure can be used to obtain operators in the noncommutative theory which are holographically dual to supergravity modes.

Volume preserving diffeomorphism and noncommutative branes

We give a representation of the volume preserving diffeomorphism of $\bR^p$ in terms of the noncommutative (p-2)-branes whose kinetic term is described by the Hopf term. In the static gauge, the (p-2)-brane can be described by the free fields and it suggests that the quantization of the algebra is possible.

Closed string brane-like states, brane bound states and noncommutative branes

We study the mass and different RR charge distributions of the BPS ( p, p−2)-brane bound states in the closed string brane-like σ-model. We show that such brane bound states can be realized by introducing a constant B field in the closed string theory. In addition we show that the worldvolume coordinates of these brane bound states turn out to be noncommutative.