On Superspace Chern-Simons-like Terms

We search for superspace Chern-Simons-like higher-derivative terms in the low energy effective actions of supersymmetric theories in four dimensions. Superspace Chern-Simons-like terms are those gauge-invariant terms which cannot be written solely in terms of field strength superfields and covariant derivatives, but in which a gauge potential superfield appears explicitly. We find one class of such four-derivative terms with N=2 supersymmetry which, though locally on the Coulomb branch can be written solely in terms of field strengths, globally cannot be. These terms are classified by certain Dolbeault cohomology classes on the moduli space. We include a discussion of other examples of terms in the effective action involving global obstructions on the Coulomb branch.Comment: 23 pages; a reference and an author email correcte

Looping on the Bloch sphere: Oscillatory effects in dephasing of qubits subject to broad-spectrum noise

For many implementations of quantum computing, 1/f and other types of broad-spectrum noise are an important source of decoherence. An important step forward would be the ability to back out the characteristics of this noise from qubit measurements and to see if it leads to new physical effects. For certain types of qubits, the working point of the qubit can be varied. Using a new mathematical method that is suited to treat all working points, we present theoretical results that show how this degree of freedom can be used to extract noise parameters and to predict a new effect: noise-induced looping on the Bloch sphere. We analyze data on superconducting qubits to show that they are very near the parameter regime where this looping should be observed.Comment: 4 pages, 3 figure

Explicit construction of nilpotent covariants in N=4 SYM

Some aspects of correlation functions in N=4 SYM are discussed. Using N=4 harmonic superspace we study two and three-point correlation functions which are of contact type and argue that these contact terms will not affect the non-renormalisation theorem for such correlators at non-coincident points. We then present a perturbative calculation of a five-point function at two loops in N=2 harmonic superspace and verify that it reproduces the derivative of the previously found four-point function with respect to the coupling. The calculation of this four-point function via the five-point function turns out to be significantly simpler than the original direct calculation. This calculation also provides an explicit construction of an N=2 component of an N=4 five-point nilpotent covariant that violates U(1)_Y symmetry.Comment: 20 pages, standard late

Supersymmetric Lorentz-Covariant Hyperspaces and self-duality equations in dimensions greater than (4|4)

We generalise the notions of supersymmetry and superspace by allowing generators and coordinates transforming according to more general Lorentz representations than the spinorial and vectorial ones of standard lore. This yields novel SO(3,1)-covariant superspaces, which we call hyperspaces, having dimensionality greater than (4|4) of traditional super-Minkowski space. As an application, we consider gauge fields on complexifications of these superspaces; and extending the concept of self-duality, we obtain classes of completely solvable equations analogous to the four-dimensional self-duality equations.Comment: 29 pages, late

Nonlinear acoustic and microwave absorption in glasses

A theory of weakly-nonlinear low-temperature relaxational absorption of acoustic and electromagnetic waves in dielectric and metallic glasses is developed. Basing upon the model of two-level tunneling systems we show that the nonlinear contribution to the absorption can be anomalously large. This is the case at low enough frequencies, where freqeuency times the minimal relaxation time for the two-level system are much less than one. In dielectric glasses, the lowest-order nonlinear contribution is proportional to the wave's intensity. It is negative and exhibits anomalous frequency and temperature dependencies. In metallic glasses, the nonlinear contribution is also negative, and it is proportional to the square root of the wave's intensity and to the frequency. Numerical estimates show that the predicted nonlinear contribution can be measured experimentally

The characteristic exponents of the falling ball model

We study the characteristic exponents of the Hamiltonian system of $n$ ($\ge 2$) point masses $m_1,\dots,m_n$ freely falling in the vertical half line $\{q|\, q\ge 0\}$ under constant gravitation and colliding with each other and the solid floor $q=0$ elastically. This model was introduced and first studied by M. Wojtkowski. Hereby we prove his conjecture: All relevant characteristic (Lyapunov) exponents of the above dynamical system are nonzero, provided that $m_1\ge\dots\ge m_n$ (i. e. the masses do not increase as we go up) and $m_1\ne m_2$

Four Dimensional Integrable Theories

There exist many four dimensional integrable theories. They include self-dual gauge and gravity theories, all their extended supersymmetric generalisations, as well the full (non-self-dual) N=3 super Yang-Mills equations. We review the harmonic space formulation of the twistor transform for these theories which yields a method of producing explicit connections and metrics. This formulation uses the concept of harmonic space analyticity which is closely related to that of quaternionic analyticity. (Talk by V. Ogievetsky at the G\"ursey Memorial Conference I, Istanbul, June 1994)Comment: 11 pages, late

Nonlinearly driven Landau-Zener transition with telegraph noise

We study Landau-Zener like dynamics of a qubit influenced by transverse random telegraph noise. The telegraph noise is characterized by its coupling strength, $v$ and switching rate, $\gamma$. The qubit energy levels are driven nonlinearly in time, \propto \sign(t)|t|^\nu, and we derive the transition probability in the limit of sufficiently fast noise, for arbitrary exponent $\nu$. The longitudinal coherence after transition depends strongly on $\nu$, and there exists a critical $\nu_c$ with qualitative difference between $\nu< \nu_c$ and $\nu > \nu_c$. When $\nu<\nu_c$ the end state is always fully incoherent with equal population of both quantum levels, even for arbitrarily weak noise. For $\nu>\nu_c$ the system keeps some coherence depending on the strength of the noise, and in the limit of weak noise no transition takes place. For fast noise $\nu_c=1/2$, while for slow noise $\nu_c<1/2$ and it depends on $\gamma$. We also discuss transverse coherence, which is relevant when the qubit has a nonzero minimum energy gap. The qualitative dependency on $\nu$ is the same for transverse as for longitudinal coherence. The state after transition does in general depend on $\gamma$. For fixed $v$, increasing $\gamma$ decreases the final state coherence when $\nu<1$ and increase the final state coherence when $\nu>1$. Only the conventional linear driving is independent of $\gamma$.Comment: 7 pages, 5 figure

On the next-to-leading-order correction to the effective action in N=2 gauge theories

I attempt to analyse the next-to-leading-order non-holomorphic contribution to the Wilsonian low-energy effective action in the four-dimensional N=2 gauge theories with matter, from the manifestly N=2 supersymmeric point of view, by using the harmonic superspace. The perturbative one-loop correction is found to be in agreement with the N=1 superfield calculations of de Wit, Grisaru and Rocek. The previously unknown coefficient in front of this non-holomorphic correction is calculated. A special attention is devoted to the N=2 superconformal gauge theories, whose one-loop non-holomorphic contribution is likely to be exact, even non-perturbatively. This leading (one-loop) non-holomorphic contribution to the LEEA of the N=2 superconformally invariant gauge field theories is calculated, and it does not vanish, similarly to the case of the N=4 super-Yang-Mills theory.Comment: 15 pages, LaTeX; changes in the abstract and in sect.

A self-consistent quantum master equation approach to molecular transport

We propose a self-consistent generalized quantum master equation (GQME) to describe electron transport through molecular junctions. In a previous study [M.Esposito and M.Galperin. Phys. Rev. B 79, 205303 (2009)], we derived a time-nonlocal GQME to cure the lack of broadening effects in Redfield theory. To do so, the free evolution used in the Born-Markov approximation to close the Redfield equation was replaced by a standard Redfield evolution. In the present paper, we propose a backward Redfield evolution leading to a time-local GQME which allows for a self-consistent procedure of the GQME generator. This approach is approximate but properly reproduces the nonequilibrium steady state density matrix and the currents of an exactly solvable model. The approach is less accurate for higher moments such as the noise.Comment: 9 pages, 4 figure