We demonstrate that for the sine-Gordon theory at the free fermion point, the 2point correlation functions of the fields exp(iαΦ) for 0 < α < 1 can be parameterized in terms of a solution to a sinh-Gordon-like equation. This result is derived by summing over intermediate multiparticle states and using the form factors to express this as a Fredholm determinant. The proof of the differential equa...

We establish Fredholm properties for a class of nonlocal differential operators. Using mild convergence and localization conditions on the nonlocal terms, we also show how to compute Fredholm indices via a generalized spectral flow, using crossing numbers of generalized spatial eigenvalues. We illustrate possible applications of the results in a nonlinear and a linear setting. We first prove th...

The calculation of low frequency expansions for acoustic wave scattering has been under thorough investigation many decades due to their utility in technological applications. In the present work, we revisit Low Frequency Scattering theory, and provide theoretical framework a new algorithmic procedure deriving coefficients total pressure field, produced by plane excitation an arbitrary, convex ...

Under minimal assumptions, we characterize the Fredholmity and compute the Fredholm index of abstract differential operators −d/dt + A(·) acting on spaces of functions f : R → X. Here A(t) are (in general) unbounded operators on the Banach space X and our results are formulated in terms of exponential dichotomies on two halflines for the propagtor solving the evolution equation u̇(t) = A(t)u(t) ...

From Corollary 3.5 in [Berkani, M; Sarih, M.; Studia Math. 148 (2001), 251– 257] we know that if S, T are commuting B-Fredholm operators acting on a Banach space X, then ST is a B-Fredholm operator. In this note we show that in general we do not have ind(ST ) = ind(S) + ind(T ), contrarily to what has been announced in Theorem 3.2 in [Berkani, M; Proc. Amer.Math. Soc. 130 (2002), 1717–1723]. Ho...

This paper concerns Fredholm theory in several variables, and its applications to Hilbert spaces of analytic functions. One feature is the introduction of ideas from commutative algebra to operator theory. Specifically, we introduce a method to calculate the Fredholm index of a pair of commuting operators. To achieve this, we define and study the Hilbert space analogs of Samuel multiplicities i...

Wiener-Hopf plus Hankel operators acting between Lebesgue spaces on the real line are studied in view of their invertibility, one sided-invertibility, Fredholm property, and the so-called n and d–normal properties. This is done in two different cases: (i) when the Fourier symbols of the operators are unitary functions, and (ii) when the Fourier symbols are related with sectorial elements appear...

The Fredholm properties of Toeplitz operators on the Bergman space A have been well-known for continuous symbols since the 1970s. We investigate the case p = 1 with continuous symbols under a mild additional condition, namely that of the logarithmic vanishing mean oscillation in the Bergman metric. Most differences are related to boundedness properties of Toeplitz operators acting on A that ari...

For smooth hyperbolic dynamical systems and smooth weights, we relate Ruelle transfer operators with dynamical Fredholm determinants and dynamical zeta functions: First, we establish bounds for the essential spectral radii of the transfer operator on new spaces of anisotropic distributions, improving our previous results [7]. Then we give a new proof of Kitaev’s [17] lower bound for the radius ...

This paper studies Dirac operators on end-periodic spin manifolds of dimension at least 4. We provide a necessary and sufficient condition for such an operator to be Fredholm for a generic end-periodic metric. We make use of end-periodic Dirac operators to give an analytical interpretation of an invariant of non-orientable smooth 4-manifolds due to Cappell and Shaneson. From this interpretation...