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Search Results: 1 - 10 of 535 matches for " Gernot Akemann "
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Universal correlators for multi-arc complex matrix models
Gernot Akemann
Physics , 1997, DOI: 10.1016/S0550-3213(97)00552-X
Abstract: The correlation functions of the multi-arc complex matrix model are shown to be universal for any finite number of arcs. The universality classes are characterized by the support of the eigenvalue density and are conjectured to fall into the same classes as the ones recently found for the hermitian model. This is explicitly shown to be true for the case of two arcs, apart from the known result for one arc. The basic tool is the iterative solution of the loop equation for the complex matrix model with multiple arcs, which provides all multi-loop correlators up to an arbitrary genus. Explicit results for genus one are given for any number of arcs. The two-arc solution is investigated in detail, including the double-scaling limit. In addition universal expressions for the string susceptibility are given for both the complex and hermitian model.
Loop equations for multi-cut matrix models
Gernot Akemann
Physics , 1995,
Abstract: The loop equation for the complex one-matrix model with a multi-cut structure is derived and solved in the planar limit. An iterative scheme for higher genus contributions to the free energy and the multi-loop correlators is presented for the two-cut model, where explicit results are given up to and including genus two. The double-scaling limit is analyzed and the relation to the one-cut solution of the hermitian and complex one-matrix model is discussed.
Non-Hermitian extensions of Wishart random matrix ensembles
Gernot Akemann
Physics , 2011, DOI: 10.5506/APhysPolB.42.901
Abstract: We briefly review the solution of three ensembles of non-Hermitian random matrices generalizing the Wishart-Laguerre (also called chiral) ensembles. These generalizations are realized as Gaussian two-matrix models, where the complex eigenvalues of the product of the two independent rectangular matrices are sought, with the matrix elements of both matrices being either real, complex or quaternion real. We also present the more general case depending on a non-Hermiticity parameter, that allows us to interpolate between the corresponding three Hermitian Wishart ensembles with real eigenvalues and the maximally non-Hermitian case. All three symmetry classes are explicitly solved for finite matrix size NxM for all complex eigenvalue correlations functions (and real or mixed correlations for real matrix elements). These are given in terms of the corresponding kernels built from orthogonal or skew-orthogonal Laguerre polynomials in the complex plane. We then present the corresponding three Bessel kernels in the complex plane in the microscopic large-N scaling limit at the origin, both at weak and strong non-Hermiticity with M-N greater or equal to 0 fixed.
A Generalisation of Dyson's Integration Theorem for Determinants
Gernot Akemann,Leonid Shifrin
Physics , 2007, DOI: 10.1088/1751-8113/40/32/F01
Abstract: Dyson's integration theorem is widely used in the computation of eigenvalue correlation functions in Random Matrix Theory. Here we focus on the variant of the theorem for determinants, relevant for the unitary ensembles with Dyson index beta = 2. We derive a formula reducing the (n-k)-fold integral of an n x n determinant of a kernel of two sets of arbitrary functions to a determinant of size k x k. Our generalisation allows for sets of functions that are not orthogonal or bi-orthogonal with respect to the integration measure. In the special case of orthogonal functions Dyson's theorem is recovered.
Equivalence of QCD in the epsilon-regime and chiral Random Matrix Theory with or without chemical potential
Francesco Basile,Gernot Akemann
Physics , 2007, DOI: 10.1088/1126-6708/2007/12/043
Abstract: We prove that QCD in the epsilon-regime of chiral Perturbation Theory is equivalent to chiral Random Matrix Theory for zero and both non-zero real and imaginary chemical potential mu. To this aim we prove a theorem that relates integrals over fermionic and bosonic variables to super-Hermitian or super-Unitary groups also called superbosonization. Our findings extend previous results for the equivalence of the partition functions, spectral densities and the quenched two-point densities. We can show that all k-point density correlation functions agree in both theories for an arbitrary number of quark flavors, for either mu=0 or mu=/=0 taking real or imaginary values. This implies the equivalence for all individual k-th eigenvalue distributions which are particularly useful to determine low energy constants from Lattice QCD with chiral fermions.
Statistics of Real Eigenvalues in Ginibre's Ensemble of Random Real Matrices
Eugene Kanzieper,Gernot Akemann
Physics , 2005, DOI: 10.1103/PhysRevLett.95.230201
Abstract: The integrable structure of Ginibre's Orthogonal Ensemble of random matrices is looked at through the prism of the probability "p_{n,k}" to find exactly "k" real eigenvalues in the spectrum of an "n" by "n" real asymmetric Gaussian random matrix. The exact solution for the probability function "p_{n,k}" is presented, and its remarkable connection to the theory of symmetric functions is revealed. An extension of the Dyson integration theorem is a key ingredient of the theory presented.
Random Matrix Theory for the Hermitian Wilson Dirac Operator and the chGUE-GUE Transition
Gernot Akemann,Taro Nagao
Physics , 2011, DOI: 10.1007/JHEP10(2011)060
Abstract: We introduce a random two-matrix model interpolating between a chiral Hermitian (2n+nu)x(2n+nu) matrix and a second Hermitian matrix without symmetries. These are taken from the chiral Gaussian Unitary Ensemble (chGUE) and Gaussian Unitary Ensemble (GUE), respectively. In the microscopic large-n limit in the vicinity of the chGUE (which we denote by weakly non-chiral limit) this theory is in one to one correspondence to the partition function of Wilson chiral perturbation theory in the epsilon regime, such as the related two matrix-model previously introduced in refs. [20,21]. For a generic number of flavours and rectangular block matrices in the chGUE part we derive an eigenvalue representation for the partition function displaying a Pfaffian structure. In the quenched case with nu=0,1 we derive all spectral correlations functions in our model for finite-n, given in terms of skew-orthogonal polynomials. The latter are expressed as Gaussian integrals over standard Laguerre polynomials. In the weakly non-chiral microscopic limit this yields all corresponding quenched eigenvalue correlation functions of the Hermitian Wilson operator.
Dropping the independence: singular values for products of two coupled random matrices
Gernot Akemann,Eugene Strahov
Physics , 2015,
Abstract: We study the singular values of the product of two coupled rectangular random matrices as a determinantal point process. Each of the two factors is given by a parameter dependent linear combination of two independent, complex Gaussian random matrices, which is equivalent to a coupling of the two factors via an Itzykson-Zuber term. We prove that the squared singular values of such a product form a biorthogonal ensemble and establish its exact solvability. The parameter dependence allows us to interpolate between the singular value statistics of the Laguerre ensemble and that of the product of two independent complex Ginibre ensembles which are both known. We give exact formulae for the correlation kernel in terms of a complex double contour integral, suitable for the subsequent asymptotic analysis. In particular, we derive a Christoffel-Darboux type formula for the correlation kernel, based on a five term recurrence relation for our biorthogonal functions. It enables us to find its scaling limit at the origin representing a hard edge. The resulting limiting kernel coincides with the universal Meijer G-kernel found by several authors in different ensembles. We show that the central limit theorem holds for the linear statistics of the singular values and give the limiting variance explicitly.
Finite volume corrections to LECs in Wilson and staggered ChPT
Gernot Akemann,Fabrizio Pucci
Physics , 2012,
Abstract: We study the simultaneous effect of finite volume and finite lattice spacing corrections in the framework of chiral perturbation theory (ChPT) in the epsilon regime, for both the Wilson and staggered formulations. In particular the finite volume corrections to the low energy constants (LECs) in Wilson and staggered ChPT are computed to next-to-leading order (NLO) in the \epsilon-expansion. For Wilson with N_f = 2 flavours and staggered with generic N_f the partition function at NLO can be rewritten as the LO partition function with renormalized effective LECs.
Exploring the Aoki regime
Gernot Akemann,Fabrizio Pucci
Physics , 2012, DOI: 10.1007/JHEP06(2013)059
Abstract: We compute next-to-leading order (NLO) corrections in the \epsilon-regime of Wilson (WChPT) and Staggered Chiral Perturbation Theory (SChPT). A difference between the two is that in WChPT already at NLO, that is at O(\epsilon^2), new low energy constants (LECs) contribute, whereas in SChPT they only enter at O(\epsilon^4). We first determine the NLO corrections in WChPT for SU(2), and for U(N_f) at fixed index. This implies finite-volume corrections to the phase boundary between the Aoki phase and the Sharpe-Singleton scenario via corrections to the mean field potential. We also compute NLO corrections to the two-point function in the scalar and pseudo-scalar sector in WChPT. Turning to SChPT we determine the NLO corrections to the LECs and their effect on the taste splitting. Here the NLO partition function can be written as the leading order one with renormalized couplings, thus preserving the equivalence to staggered chiral random matrix theory at NLO for any number of flavors N_f. In WChPT this relation only appears to hold for SU(2).
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