The Confining String from the Soft Dilaton Theorem

A candidate for the confining string of gauge theories is constructed via a representation of the ultraviolet divergences of quantum field theory by a closed string dilaton insertion, computed through the soft dilaton theorem. The resulting (critical) confining string is conformally invariant, singles out naturally $d=4$ dimensions, and can not be used to represent theories with Landau poles.Comment: 13 pages, two figures Clarifying remark added. Typos correcte

On the String Description of Confinement

A non supersymmetric string background, directly derived from the string soft dilaton theorem, is used to compute, in the semiclassical approximation, the expectation value of Wilson loops in static gauge. The resulting potential shares common features with the one obtained through Schwarzschild-anti de Sitter spacetime metrics. In particular a linear confining potential appears naturally.Comment: LaTeX,8 pages, 3 figures.Acknowledgements adde

Holography and the C-Theorem

We review the geometric definition of C-function in the context of field theories that admit a holographic gravity dual.Comment: Contribution to the proceedings of the TMR 2000 Paris Conferenc

Initial conditions for inflation and the energy scale of SUSY-breaking from the (nearly) gaussian sky

We show how general initial conditions for small field inflation can be obtained in multi-field models. This is provided by non-linear angular friction terms in the inflaton that provide a phase of non-slow-roll inflation before the slow-roll inflation phase. This in turn provides a natural mechanism to star small-field slow-roll at nearly zero velocity for arbitrary initial conditions. We also show that there is a relation between the scale of SUSY breaking sqrt (f) and the amount of non-gaussian fluctuations generated by the inflaton. In particular, we show that in the local non-gaussian shape there exists the relation sqrt (f) = 10^{13} GeV sqrt (f_NL). With current observational limits from Planck, and adopting the minimum amount of non-gaussian fluctuations allowed by single-field inflation, this provides a very tight constraint for the SUSY breaking energy scale sqrt (f) = 3-7 x 10^{13} GeV at 95% confidence. Further limits, or detection, from next year's Planck polarisation data will further tighten this constraint by a factor of two. We highlight that the key to our approach is to identify the inflaton with the scalar component of the goldstino superfield. This superfield is universal and implements the dynamics of SUSY breaking as well as superconformal breaking.Comment: Invited talk at the BW2013 meetin

On the Influence of Spatial Dispersion on the Performance of Graphene-Based Plasmonic Devices

We investigate the effect of spatial dispersion phenomenon on the performance of graphene-based plasmonic devices at THz. For this purpose, two different components, namely a phase shifter and a low-pass filter, are taken from the literature, implemented in different graphene-based host waveguides, and analyzed as a function of the surrounding media. In the analysis, graphene conductivity is modeled first using the Kubo formalism and then employing a full-$k_\rho$ model which accurately takes into account spatial dispersion. Our study demonstrates that spatial dispersion up-shifts the frequency response of the devices, limits their maximum tunable range, and degrades their frequency response. Importantly, the influence of this phenomenon significantly increases with higher permittivity values of the surrounding media, which is related to the large impact of spatial dispersion in very slow waves. These results confirm the necessity of accurately assessing non-local effects in the development of practical plasmonic THz devices.Comment: 5 pages, 18 figures, 2 table