The dynamics of coset dimensional reduction

The evolution of multiple scalar fields in cosmology has been much studied, particularly when the potential is formed from a series of exponentials. For a certain subclass of such systems it is possible to get `assisted` behaviour, where the presence of multiple terms in the potential effectively makes it shallower than the individual terms indicate. It is also known that when compactifying on coset spaces one can achieve a consistent truncation to an effective theory which contains many exponential terms, however, if there are too many exponentials then exact scaling solutions do not exist. In this paper we study the potentials arising from such compactifications of eleven dimensional supergravity and analyse the regions of parameter space which could lead to scaling behaviour.Comment: 27 pages, 4 figures; added citation

Cosmology with Twisted Tori

We consider the cosmological role of the scalar fields generated by the compactification of 11-dimensional Einstein gravity on a 7D elliptic twisted torus, which has the attractive features of giving rise to a positive semi-definite potential, and partially fixing the moduli. This compactification is therefore relevant for low energy M-theory, 11D supergravity. We find that slow-roll inflation with the moduli is not possible, but that there is a novel scaling solution in Friedmann cosmologies in which the massive moduli oscillate but maintain a constant energy density relative to the background barotropic fluid

One-loop Higgs mass finiteness in supersymmetric Kaluza-Klein theories

We analyze the one-loop ultraviolet sensitivity of the Higgs mass in a five-dimensional supersymmetric theory compactified on the orbifold S^1/Z_2, with superpotential localized on a fixed-point brane. Four-dimensional supersymmetry is broken by Scherk-Schwarz boundary conditions. Kaluza-Klein interactions are regularized by means of a brane Gaussian distribution along the extra dimension with length l_s\simeq\Lambda^{-1}_s, where \Lambda_s is the cutoff of the five-dimensional theory. The coupling of the n-mode, with mass M^{(n)}, acquires the n-dependent factor exp{-(M^{(n)}/\Lambda_s)^2/2}, which makes it to decouple for M^{(n)}\gg \Lambda_s. The sensitivity of the Higgs mass on \Lambda_s is strongly suppressed and quadratic divergences cancel by supersymmetry. The one-loop correction to the Higgs mass is finite and equals, for large values of \Lambda_s, the value obtained by the so-called KK-regularization.Comment: 8 pages, 1 figure. The discussion on the distribution giving rise to couplings suppressed by exp(-M/Lambda) is revised and the result is finite and equals that of the Gaussian cas

Dual strings and magnetohydrodynamics

We investigate whether dual strings could be solutions of the magnetohydrodynamics equations in the limit of infinite conductivity. We find that the induction equation is satisfied, and we discuss the Navier-Stokes equation (without viscosity) with the Lorentz force included. We argue that the dual string equations (with a non-universal maximum velocity) should describe the large scale motion of narrow magnetic flux tubes, because of a large reparametrization (gauge) invariance of the magnetic and electric string fields. It is shown that the energy-momentum tensor for the dual string can be reinterpreted as an energy-momentum tensor for magnetohydrodynamics, provided certain conditions are satisfied. We also give a brief discussion of the case when magnetic monopoles are included, and indicate how this can lead to a non-relativistic "electrohydrodynamics" picture of confinement.Comment: 10 pages. LaTex. A minor correction has been mad

The Effective Potential And Additional Large Radius Compactified Space-Time Dimensions

The consequences of large radius extra space-time compactified dimensions on the four dimensional one loop effective potential are investigated for a model which includes scalar self interactions and Yukawa coupling to fermions. The Kaluza-Klein tower of states associated with the extra compact dimensions shifts the location of the effective potential minimum and modifies its curvature. The dependence of these effects on the radius of the extra dimension is illustrated for various choices of coupling constants and masses. For large radii, the consequence of twisting the fermion boundary condition on the compactified dimensions is numerically found to produce but a negligible effect on the effective potential.Comment: 14 pages, LaTeX, 6 Postscript figure

Testing the equivalence principle: why and how?

Part of the theoretical motivation for improving the present level of testing of the equivalence principle is reviewed. The general rationale for optimizing the choice of pairs of materials to be tested is presented. One introduces a simplified rationale based on a trichotomy of competing classes of theoretical models.Comment: 11 pages, Latex, uses ioplppt.sty, submitted to Class. Quantum Gra

Renormalization of Boundary Fermions and World-Volume Potentials on D-branes

We consider a sigma model formulation of open string theory with boundary fermions carrying Chan-Paton charges at the string ends. This formalism is particularly suitable for studying world-volume potentials on D-branes. We perform explicit two-loop sigma model computations of the potential T-dual to the non-abelian Born-Infeld action. We also discuss the world-volume couplings of NS fluxes which are responsible for Myers' dielectric effect.Comment: 17 pages, 8 figure

Potential and mass-matrix in gauged N=4 supergravity

We discuss the potential and mass-matrix of gauged N=4 matter coupled supergravity for the case of six matter multiplets, extending previous work by considering the dependence on all scalars. We consider all semi-simple gauge groups and analyse the potential and its first and second derivatives in the origin of the scalar manifold. Although we find in a number of cases an extremum with a positive cosmological constant, these are not stable under fluctuations of all scalar fields.Comment: 28 pages, LaTe

Quantising Gravity Using Physical States of a Superstring

A symmetric zero mass tensor of rank two is constructed using the superstring modes of excitation which satisfies the physical state constraints of a superstring. These states have one to one correspondence with quantised operators and are shown to be the absorption and emission quanta of the Minkowski space Lorentz tensors using the Gupta-Bleuler method of quantisation. The principle of equivalence makes the tensor identical to the metric tensor at any arbitrary space-time point. The propagator for the quantised field is deduced. The gravitational interaction is switched on by going over from ordinary derivatives to coderivatives.The Riemann-Christoffel affine connections are calculated and the weak field Ricci tensor $R^{0}_{\mu \nu}$ is shown to vanish. The interaction part $R^{int}_{\mu \nu}$ is found out and the exact $R_{\mu \nu}$ of theory of gravity is expressed in terms of the quantised metric. The quantum mechanical self energy of the gravitational field, in vacuum, is shown to vanish. It is suggested that quantum gravity may be renormalisable by the use of the physical ground states of the superstring theory.Comment: 14 page

T-duality of NSR superstring: The worldsheet perspective

We formulate target space duality symmetry of NSR superstring from the perspectives of worldsheet. The worldsheet action is presented in the superspace formalism in the presence of massless backgrounds. We start from a ${\hat D}$-dimensional target space worldsheet action and compactify the theory on a d-dimensional torus, $T^d$. It is assumed that the backgrounds are independent of compact (super)coordinates. We adopt the formalism of our earlier work to introduce dual supercoordinates along compact directions and introduce the corresponding dual backgrounds. It is demonstrated that combined equations of motion of the two sets of coordinates can be expressed in a manifestly $O(d,d)$ covariant form analogous to the equations of motions for closed bosonic string derived by us. Furthermore, we show that the vertex operators associated with excited massive levels of NSR string can be expressed in an $O(d,d)$ invariant form generalizing earlier result for closed bosonic string.Comment: 21 page