Discrete Symmetries (C,P,T) in Noncommutative Field Theories

In this paper we study the invariance of the noncmmutative gauge theories under C, P and T transformations. For the noncommutative space (when only the spatial part of $\theta$ is non-zero) we show that NCQED is Parity invariant. In addition, we show that under charge conjugation the theory on noncommutative $R^4_{\theta}$ is transformed to the theory on $R^4_{-\theta}$, so NCQED is a CP violating theory. The theory remains invariant under time reversal if, together with proper changes in fields, we also change $\theta$ by $-\theta$. Hence altogether NCQED is CPT invariant. Moreover we show that the CPT invariance holds for general noncommutative space-time.Comment: Revtex File, 4 pages, no figures, minor changes from previous verion. To appear in Phys. Rev. Let

One Loop Renormalizability of Supersymmetric Yang-Mills Theories on Noncommutative Two-Torus

We argue that Yang-Mills theory on noncommutative torus, expressed in the Fourrier modes, is described by a gauge theory in a usual commutative space, the gauge group being a generalization of the area-preserving diffeomorphisms to the noncommutative case. In this way, performing the loop calculation in this gauge theory in the continuum limit we show that this theory is {\it one loop renormalizable}, and discuss the UV and IR limits. The moduli space of the vacua of the noncommutative super Yang-Mills theories in (2+1) dimensions is discussed.Comment: 16 pp, one figure, v2: One reference added, typos corrected. v3: minor exchange

More on Mixed Boundary Conditions and D-branes Bound States

In this article, applying different types of boundary conditions; Dirichlet, Neumann, or Mixed, on open strings we realize various new brane bound states in string theory. Calculating their interactions with other D-branes, we find their charge densities and their tension. A novel feature of $(p-2,p)$ brane bound state is its "non-commutative" nature which is manifestly seen both in the open strings mode expansions and in their scattering off a $D_p$-brane. Moreover we study three or more object bound states in string theory language. Finally we give a M-theoretic picture of these bound states.Comment: Latex file, pages, No Figure

Classification of Different Branes at Angles

In this paper, we consider two D-branes rotated with respect to each other, and argue that in this way one can find brane configurations preserving {1 \f 16} of SUSY. Also we classify different brane configurations preserving {1 \f 2}, {1 \f 4}, {3 \f 16},{1 \f 8}, {1 \f 16} of SUSY.Comment: Tex, 11 page, no figure

Noncommutative Open String Theories and Their Dualities

The recently found non-critical open string theories is reviewed. These open strings, noncommutative open string theories (NCOS), arise as consistent quantum theories describing the low energy theory of D-branes in a background electric B-field in the critical limit. Focusing on the D3-brane case, we construct the most general (3+1) NCOS, which is described by four parameters. We study S and T -dualities of these theories and argue the existence of a U-duality group.Comment: 10 pages, no figures, The invited talk, presented in the conference "Brane New World and Noncommutative Geometry", Torino, Villa Gualino,(Italy) October, 200

Gauged M-flation After BICEP2

In view of the recent BICEP2 results [arXiv:1403.3985] which may be attributed to the observation of B-modes polarization of the CMB with tensor-to-scalar ratio $r=0.2_{-0.05}^{+0.07}$, we revisit M-flation model. Gauged M-flation is a string theory motivated inflation model with Matrix valued scalar inflaton fields in the adjoint representation of a $U(N)$ Yang-Mills theory. In continuation of our previous works, we show that in the M-flation model induced from a supersymmetric 10d background probed by a stack of $N$ D3-branes, the "effective inflaton" $\phi$ has a double-well Higgs-like potential, with minima at $\phi=0,\mu$. We focus on the $\phi>\mu$, symmetry-breaking region. We thoroughly examine predictions of the model for $r$ in the $2\sigma$ region allowed for $n_S$ by the Planck experiment. As computed in [arXiv:0903.1481], for $N_e=60$ and $n_S=0.96$ we find $r\simeq 0.2$, which sits in the sweet spot of BICEP2 region for $r$. We find that with increasing $\mu$ arbitrarily, $n_S$ cannot go beyond $\simeq 0.9670$. As $n_S$ varies in the $2\sigma$ range which is allowed by Planck and could be reached by the model, $r$ varies in the range $[0.1322,0.2623]$. Future cosmological experiments, like the CMBPOL, that confines $n_S$ with $\sigma(n_S)=0.0029$ can constrain the model further. Also, in this region of potential, for $n_S=0.9603$, we find that the largest isocurvature mode, which is uncorrelated with curvature perturbations, has a power spectrum with the amplitude of order $10^{-11}$ at the end of inflation. We also discuss the range of predictions of $r$ in the hilltop region, $\phi< \mu$.Comment: v1:16 pages, 9 figures; v2: matched the published versio

Boundary Conditions as Dirac Constraints

In this article we show that boundary conditions can be treated as Lagrangian and Hamiltonian constraints. Using the Dirac method, we find that boundary conditions are equivalent to an infinite chain of second class constraints which is a new feature in the context of constrained systems. Constructing the Dirac brackets and the reduced phase space structure for different boundary conditions, we show why mode expanding and then quantizing a field theory with boundary conditions is the proper way. We also show that in a quantized field theory subjected to the mixed boundary conditions, the field components are noncommutative.Comment: 18 pp, Latex, minor changes, typos correcte