Nonzero String Tension Research Articles

Predicted constraints on cosmic string tension from Planck and future CMB polarization measurements

We perform a Fisher matrix calculation of the predicted uncertainties on estimates of the cosmic string tension Gmu from upcoming observational data (namely, cosmic microwave background power spectra from the Planck satellite and an idealized future polarization experiment). We employ simulations that are more general than others commonly used in the literature, leaving the mean velocity of strings, correlation length of the string network, and "wiggliness" (which parametrizes smaller-scale structure along the strings) as free parameters that can be observationally measured. In a new code, StringFast, we implement a method for efficient computation of the C_l spectra induced by a network of strings, which is fast enough to be used in Markov Chain Monte Carlo analyses of future data. Performing a calculation with the string parameters left free results in projected constraints on Gmu that are larger than those obtained by fixing their values a priori, typically by a factor of ~2-7. We also find that if Gmu is equal to the current observational maximum, Planck will be able to make a confident detection of strings. However, if Gmu is two orders of magnitude smaller, even a perfect, lensing-free measurement of polarization power spectra will not be able to detect a nonzero string tension at better than 2 sigma confidence.

TWO-LOOP WORLDSHEET EFFECTIVE ACTION

We are studying quantum corrections in the earlier proposed string theory based on worldsheet action which measures the linear sizes of the surfaces. At classical level the string tension is equal to zero and as it was demonstrated in the previous studies one loop correction to the classical worldsheet action generates Nambu–Goto area term, that is nonzero string tension. We extend this analysis computing the worldsheet effective action in the second order of the loop expansion. We are studying quantum corrections in the earlier proposed string theory based on worldsheet action which measures the perimeter of the surface. At the classical level the string tension is equal to zero and we demonstrate that one and two-loop corrections to the classical worldsheet action generates Nambu–Goto area term, that is nonzero string tension.

On QCD string theory and AdS dynamics

The AdS/CFT correspondence of elementary string theory has been recently suggested as a ``microscopic'' approach to QCD string theory in various dimensions. We use the microscopic theory to show that the ultraviolet regime on the string world-sheet is mapped to the ultraviolet effects in QCD. In the case of QCD_2, a world-sheet path integral representation of QCD strings is known, in terms of a topological rigid string theory whose world-sheet supersymmetry is reminiscent of Parisi-Sourlas supersymmetry. We conjecture that the supersymmetric rigid string theory is dual to the elementary Type IIB string theory in the singular AdS background that corresponds to the large-N limit of QCD_2. We also generalize the rigid string with world-sheet Parisi-Sourlas supersymmetry to dimensions greater than two, and argue that the theory is asymptotically free, a non-zero string tension is generated dynamically through dimensional transmutation, and the theory is topological only asymptotically in the ultraviolet.

Gonihedric string equation

Arguing that the equation for the gonihedric string should have a generalized Dirac form, we found a new equation which corresponds to a symmetric solution of the Majorana commutation relations and has a non-Jacobian form. The corresponding generalized gamma-matrices are anticommuting and guarantee unitarity at all orders of v/ c. The previous solution was in a Jacobian form and admits unitarity at zero order. Explicit formulas for the mass spectrum lead to nonzero string tension M 2 j ≥ M 2( j+1) 2. The equation does not admit tachyonic solutions, but still has unwanted ghost solutions. We discuss also new dual transformation of the Dirac equation and of the proposed generalizations.

Do classical configurations produce confinement?

We show that certain classical SU(2) pure gauge configurations give rise to a non-zero string tension. We then investigate cooled configurations generated by Monte Carlo simulations on the lattice and find similar properties. We infer evidence in favour of a classical model of confinement.

Compact three-dimensional QED: A simple example of a variational calculation in a gauge theory

We apply a simple mean field like variational calculation to compact QED in 2+1 dimensions. Our variational ansatz explicitly preserves compact gauge invariance of the theory. We reproduce in this framework all the known results, including dynamical mass generation, Polyakov scaling and the nonzero string tension. It is hoped that this simple example can be a useful reference point for applying similar approximation techniques to nonabelian gauge theories.

GONIHEDRIC STRING AND ASYMPTOTIC FREEDOM

Very few natural basic principles allow to extend Feynman integral over the paths to an integral over the surfaces so that they coincide at long time scale, that is when the surface degenerates into a single particle world line. In the classical approximation the loop Green functions have perimeter behavior. That corresponds to the free quarks. Quantum fluctuations of the surface generate nonzero string tension, that is the area law and we have quark confinement. In this string theory confinement and asymptotic freedom can coexist.