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A huge amount of thermal energy is available close to material surfaces in radiative and non-radiative states, which can be useful for matter characterization or for energy devices. One way to harness this near-field energy is to scatter it to the far field. Another way is to bring absorbers close to thermal emitters, and the advent of a full class of novel photonic devices exploiting thermal photons in the near field has been predicted in the last two decades. However, efficient heat-to-electricity conversion of near-field thermal photons, i.e. the seminal building block, could not be achieved experimentally until now. Here, by approaching a micron-sized infrared photovoltaic cell at nanometric distances from a hot surface, we demonstrate conversion efficiency up to 14% leading to unprecedented electrical power density output (7500 W.m-2), orders of magnitude larger than all previous attempts. This proof of principle is achieved by using hot graphite microsphere emitters (~800 K) and indium antimonide cells, whose low bandgap energy matches the emitter infrared spectrum and which are specially designed for the near field. These results pave the way for efficient photoelectric detectors converting thermal photons directly in the near field. They also highlight that near-field thermophotovoltaic converters, which harvest radiative thermal energy in a contactless manner, are now competing with other energy-harvesting devices, such as thermoelectrics, over a large range of heat source temperatures.

We introduce thermal superspace and show how it can be used to reconcile the superfield formulation of supersymmetry with finite temperature environments, Comment: 5 pages, LaTeX. Talk presented at ``Strong and Electroweak Matter 98", Copenhagen, December 2-5 1998

Thermal superspace is characterized by Grassmann variables which are time-dependent and antiperiodic in imaginary time, with a period given by the inverse temperature. The thermal superspace approach allows to define thermal superfields obeying consistent boundary conditions and to formulate a ``super-KMS'' condition for superfield propagators. Upon constructing thermal covariantizations of the superspace derivative operators, we define thermal covariant derivatives and provide a definition of thermal chiral and antichiral superfields. Thermal covariantizations of the generators of the super-Poincar\'e algebra are also constructed, and the thermal supersymmetry algebra is computed; it has the same structure as at T=0. We then investigate realizations of this thermal supersymmetry algebra on systems of thermal fields. In doing so, we observe thermal supersymmetry breaking in terms of the lifting of the mass degeneracy, and of the non-invariance of the thermal action., Comment: Talk given at TFT'98, Regensburg (Germany), August 10-14 1998. 10 pages, no figures, RevTeX twocolumns. References added

We investigate realizations of supersymmetry at finite temperature in terms of thermal superfields, in a thermally constrained superspace: the Grassmann coordinates are promoted to be time-dependent and antiperiodic, with a period given by the inverse temperature. This approach allows to formulate a Kubo-Martin-Schwinger (KMS) condition at the level of thermal superfield propagators. The latter is proven directly in thermal superspace, and is shown to imply the correct (bosonic and fermionic) KMS conditions for the component fields. In thermal superspace, we formulate thermal covariant derivatives and supercharges and derive the thermal super-Poincar\'e algebra. Finally, we briefly investigate field realizations of this thermal supersymmetry algebra, focussing on the Wess-Zumino model. The thermal superspace formalism is used to characterize the breaking of global supersymmetry at finite temperature., Comment: 27 pages, no figures, LaTeX. Typos corrected and references added. To appear in Nucl. Phys. B

I present a criterion for all-order finiteness in N=1 SYM theories. Three applications are given; they yield all-order finite N=1 SYM models with global symmetries of the superpotential., Comment: 3 pages, plain LaTex, no figures

I outline various derivations of the non-Abelian Kubo equation, which governs the response of a quark-gluon plasma to hard thermal perturbations. In the static case, it is proven that gauge theories do not support hard thermal solitons. Explicit solutions are constructed within an SU(2) Ansatz and they are shown to support the general result. The time-dependent problem, i.e., non-Abelian plasma waves, has not been completely solved. We express and motivate the hope that the intimate relations linking the gauge-invariance condition for hard thermal loops to the equation of motion for T=0, topological Chern-Simons theory may yield new insight into this field., Comment: 9 pages, LaTex, 1 ps figure. hep-ph corrected to hep-th in paper heading

As a motivation, we first recall the possible connection of electric-magnetic duality to finiteness in N=1 super-Yang-Mills theories (SYM). Then, we present the criterion for all-order finiteness (i.e., vanishing of the beta-functions at all orders) in N=1 SYM. Finally, we apply this finiteness criterion to an SU(5) SGUT. The latter turns out to be all-order finite if one imposes additional symmetries., Comment: 17 pages, plain LaTex, no figures. Some typos corrected, references updated

Classical transport theory for colored particles is investigated and employed to derive the hard thermal loops of QCD. A formal construction of phase-space for color degrees of freedom is presented. The gauge invariance of the non-Abelian Vlasov equations is verified and used as a guiding principle in our approximation scheme.We then derive the generating functional of hard thermal loops from a constraint satisfied at leading-order by the color current. This derivation is more direct than alternative ones based on perturbative quantum field theory, and shows that hard thermal effects in hot QCD are essentially {\it classical}. As an illustration, we analyze color polarization in the QCD plasma., Comment: MIT--CTP #2320, 23 pages, Revtex

Classical transport theory is employed to analyze the hot quark-gluon plasma at the leading order in the coupling constant. A condition on the (covariantly conserved) color current is obtained. {}From this condition, the generating functional of hard thermal loops with an arbitrary number of soft external bosonic legs can be derived. Our approach, besides being more direct than alternative ones, shows that hard thermal loops are essentially classical., Comment: 8 pages, MIT CTP #2292

The actions for all classical (and consequently quantum) $BF$ theories on $n$-manifolds is proven to be given by anti-commutators of hermitian, nilpotent, scalar fermionic charges with Grassmann-odd functionals. In order to show this, the space of fields in the theory must be enlarged to include ``mass terms'' for new, non-dynamical, Grassmann-odd fields. The implications of this result on observables are examined., Comment: 12 pgs., LaTeX, MIT-CTP-2271

First, we investigate the static non-Abelian Kubo equation. We prove that it does not possess finite energy solutions; thereby we establish that gauge theories do not support hard thermal solitons. A similar argument shows that "static" instantons are absent. In addition, we note that the static equations reproduce the expected screening of the non-Abelian electric field by a gauge invariant Debye mass m=gT sqrt((N+N_F/2)/3). Second, we derive the non-Abelian Kubo equation from the composite effective action. This is achieved by showing that the requirement of stationarity of the composite effective action is equivalent, within a kinematical approximation scheme, to the condition of gauge invariance for the generating functional of hard thermal loops., Comment: 17 pages, MIT preprint CTP#2261. An Appendix [including one (appended) PS figure] presenting a numerical analysis of the static solutions has been included. A note relating our approach to alternative ones has been added. We have also added references and comments in Section III

Starting from a $D=3$, $N=4$ supersymmetric theory for matter fields, a twist with a Grassmann parity change is defined which maps the theory into a gauge fixed, abelian $BF$ theory on curved 3-manifolds. After adding surface terms to this theory, the twist is seen to map the resulting supersymmetric action to two uncoupled copies of the gauge fixed Chern-Simons action. In addition, we give a map which takes the $BF$ and Chern-Simons theories into Donaldson-Witten TQFT's. A similar construction, but with $N=2$ supersymmetry, is given in two dimensions., Comment: 19 pages, CTP #2237, LaTeX

We show that the BF theory in any space-time dimension, when quantized in a certain linear covariant gauge, possesses a vector supersymmetry. The generator of the latter together with those of the BRS transformations and of the translations form the basis of a superalgebra of the Wess-Zumino type. We give a general classification of all possible anomalies and invariant counterterms. Their absence, which amounts to ultraviolet finiteness, follows from purely algebraic arguments in the lower-dimensional cases., Comment: 27 p., Latex file