75,303 research outputs found

    Nonperturbative results for the mass dependence of the QED fermion determinant

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    The fermion determinant in four-dimensional quantum electrodynamics in the presence of O(2)XO(3) symmetric background gauge fields with a nonvanishing global chiral anomaly is considered. It is shown that the leading mass singularity of the determinant's nonperturbative part is fixed by the anomaly. It is also shown that for a large class of such fields there is at least one value of the fermion mass at which the determinant's nonperturbative part reduces to its noninteracting value.Comment: This is an extended version of the author's paper in Phys.Rev.D81(2010)10770

    Spinoza today: the current state of Spinoza scholarship

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    What I plan to do in this paper is to provide a survey of the ways in which Spinoza’s philosophy has been deployed in relation to early modern thought, in the history of ideas and in a number of different domains of contemporary philosophy, and to offer an account of how some of this research has developed. The past decade of research in Spinoza studies has been characterized by a number of tendencies; however, it is possible to identify four main domains that characterize these different lines of research: studies of Spinoza’s individual works, of its problematic concepts, from the point of view of the history of ideas, and comparative studies of Spinoza’s ideas

    Hamilton's turns as visual tool-kit for designing of single-qubit unitary gates

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    Unitary evolutions of a qubit are traditionally represented geometrically as rotations of the Bloch sphere, but the composition of such evolutions is handled algebraically through matrix multiplication [of SU(2) or SO(3) matrices]. Hamilton's construct, called turns, provides for handling the latter pictorially through the as addition of directed great circle arcs on the unit sphere S2⊂R3^2 \subset \mathbb{R}^3, resulting in a non-Abelian version of the parallelogram law of vector addition of the Euclidean translation group. This construct is developed into a visual tool-kit for handling the design of single-qubit unitary gates. As an application, it is shown, in the concrete case wherein the qubit is realized as polarization states of light, that all unitary gates can be realized conveniently through a universal gadget consisting of just two quarter-wave plates (QWP) and one half-wave plate (HWP). The analysis and results easily transcribe to other realizations of the qubit: The case of NMR is obtained by simply substituting π/2\pi/2 and π\pi pulses respectively for QWPs and HWPs, the phases of the pulses playing the role of the orientation of fast axes of these plates.Comment: 16 Pages, 14 Figures, Published versio

    Approach to Equilibrium for a Forced Burgers Equation

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    We show that approach to equilibrium in certain forced Burgers equations is implied by a decay estimate on a suitable intrinsic semigroup estimate, and we verify this estimate in a variety of cases including a periodic force.Comment: To appear in Journal of Evolution Equation

    On Local Borg-Marchenko Uniqueness Results

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    We provide a new short proof of the following fact, first proved by one of us in 1998: If two Weyl-Titchmarsh m-functions, mj(z)m_j(z), of two Schr\"odinger operators H_j = -\f{d^2}{dx^2} + q_j, j=1,2 in L2((0,R))L^2 ((0,R)), 0<R≤∞0<R\leq \infty, are exponentially close, that is, |m_1(z)- m_2(z)| \underset{|z|\to\infty}{=} O(e^{-2\Ima (z^{1/2})a}), 0<a<R, then q1=q2q_1 = q_2 a.e.~on [0,a][0,a]. The result applies to any boundary conditions at x=0 and x=R and should be considered a local version of the celebrated Borg-Marchenko uniqueness result (which is quickly recovered as a corollary to our proof). Moreover, we extend the local uniqueness result to matrix-valued Schr\"odinger operators.Comment: LaTeX, 18 page

    Uniqueness theorems in inverse spectral theory for one-dimensional Schrödinger operators

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    New unique characterization results for the potential V(x) in connection with Schrödinger operators on R and on the half-line [0,∞)are proven in terms of appropriate Krein spectral shift functions. Particular results obtained include a generalization of a well-known uniqueness theorem of Borg and Marchenko for Schrödinger operators on the half-line with purely discrete spectra to arbitrary spectral types and a new uniqueness result for Schrödinger operators with confining potentials on the entire real line

    Positive Lyapunov Exponents for Quasiperiodic Szego cocycles

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    In this paper we first obtain a formula of averaged Lyapunov exponents for ergodic Szego cocycles via the Herman-Avila-Bochi formula. Then using acceleration, we construct a class of analytic quasi-periodic Szego cocycles with uniformly positive Lyapunov exponents. Finally, a simple application of the main theorem in [Y] allows us to estimate the Lebesgue measure of support of the measure associated to certain class of C1 quasiperiodic 2- sided Verblunsky coefficients. Using the same method, we also recover the [S-S] results for Schrodinger cocycles with nonconstant real analytic potentials and obtain some nonuniform hyperbolicity results for arbitrarily fixed Brjuno frequency and for certain C1 potentials.Comment: 27 papge

    Eigenvalue estimates for non-normal matrices and the zeros of random orthogonal polynomials on the unit circle

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    We prove that for any n×nn\times n matrix, AA, and zz with ∣z∣≥∥A∥|z|\geq \|A\|, we have that \|(z-A)^{-1}\|\leq\cot (\frac{\pi}{4n}) \dist (z, \spec(A))^{-1}. We apply this result to the study of random orthogonal polynomials on the unit circle.Comment: 27 page
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