on the spectral problem for anyons we consider the spectral problem resulting from the schrodinger equation for a quantum system ofn 2 indistinguishable spinless hard core particles on a domain in two dimensional euclidian space for particles obeying fractional statistics and interacting via a repulsive hard core potential we provide a rigorous framework for analysing the spectral problem with its multi valued wave functions

computation in a single neuron hodgkin and huxley revisited a spiking neuron computes by transforming a complex dynamical input into a train of action potentials or spikes the computation performed by the neuron can be formulated as dimensional reduction or feature detection followed by a nonlinear decision function over the low dimensional space generalizations of the reverse correlation technique with white noise input provide a numerical strategy for extracting the relevant low dimensional features from experimental data and information theory can be used to evaluate the quality of the low dimensional approximation we apply these methods to analyze the simplest biophysically realistic model neuron the hodgkin huxley hh model using this system to illustrate the general methodological issues we focus on the features in the stimulus that trigger a spike explicitly eliminating the effects of interactions between spikes one can approximate this triggering feature space as a two dimensional linear subspace in the high dimensional space of input histories capturing in this way a substantial fraction of the mutual information between inputs and spike time we find that an even better approximation however is to describe the relevant subspace as two dimensional but curved in this way we can capture 90 of the mutual information even at high time resolution our analysis provides a new understanding of the computational properties of the hh model while it is common to approximate neural behavior as integrate and fire the hh model is not an integrator nor is it well described by a single threshold

fock representations of exchange algebras with involution an associative algebra ar with exchange properties generalizing the canonical anti commutation relations is considered we introduce a family of involutions in ar and construct the relative fock representations examining the positivity of the metric as an application of the general results we rigorously prove unitarity of the scattering operator of integrable models in 1 1 space time dimensions in this context the possibility of adopting various involutions in the zamolodchikov faddeev algebra is also explored

hierarchical computation in the canonical auditory cortical circuit sensory cortical anatomy has identified a canonical microcircuit underlying computations between and within layers this feed forward circuit processes information serially from granular to supragranular and to infragranular layers how this substrate correlates with an auditory cortical processing hierarchy is unclear we recorded simultaneously from all layers in cat primary auditory cortex ai and estimated spectrotemporal receptive fields strfs and associated nonlinearities spike triggered averaged strfs revealed that temporal precision spectrotemporal separability and feature selectivity varied with layer according to a hierarchical processing model strfs from maximally informative dimension mid analysis confirmed hierarchical processing of two cooperative mids identified for each neuron the first comprised the majority of stimulus information in granular layers second mid contributions and nonlinear cooperativity increased in supragranular and infragranular layers the ai microcircuit provides a valid template for three independent hierarchical computation principles increases in processing complexity strf cooperativity and nonlinearity correlate with the synaptic distance from granular layers

positive representations of general commutation relations allowing wick ordering we consider the problem of representing in hilbert space commutation relations of the form graphics where the tklij are essentially arbitrary scalar coefficients examples comprise the q canonical commutation relations introduced by greenberg bozejko and speicher and the twisted canonical anti commutation relations studied by pusz and woronowicz as well as the quantum group s u 2 using these relations any polynomial in the generators ai and their adjoints can uniquely be written in wick ordered form in which all starred generators are to the left of all unstarred ones in this general framework we define the fock representation as well as coherent representations we develop criteria for the natural scalar product in the associated representation spaces to be positive definite and for the relations to have representations by bounded operators in a hilbert space we characterize the relations between the generators ai not involving a i which are compatible with the basic relations the relations may also be interpreted as defining a non commutative differential calculus for generic coefficients tklij however all differential forms of degree 2 and higher vanish we exhibit conditions for this not to be the case and relate them to the ideal structure of the wick algebra and conditions of positivity we show that the differential calculus is compatible with the involution iff the coefficients t define a representation of the braid group this condition is also shown to imply improved bounds for the positivity of the fock representation finally we study the kms states of the group of gauge transformations defined by aj exp it aj

the characterizations of a semicircle law by the certain freeness in a c probability space in usual probability theory various characterizations of the gaussian law have been obtained for instance independence of the sample mean and the sample variance of independently identically distributed random variables characterizes the gaussian law and the property of remaining independent under rotations characterizes the gaussian random variables in this paper we consider the free analogue of such a kind of characterizations replacing independence by freeness we show that freeness of the certain pair of the linear form and the quadratic form in freely identically distributed noncommutative random variables which covers the case for the sample mean and the sample variance characterizes the semicircle law moreover we give the alternative proof for nica s result that the property of remaining free under rotations characterizes a semicircular system our proof is more direct and straightforward one

an example of a generalized brownian motion we present an example of a generalized brownian motion it is given by creation and annihilation operators on a twisted fock space ofl2 these operators fulfill for a fixed 1 1 the relationsc f c g c g c f f g 1 f g l2 we show that the distribution of these operators with respect to the vacuum expectation is a generalized gaussian distribution in the sense that all moments can be calculated from the second moments with the help of a combinatorial formula we also indicate that our brownian motion is one component of ann dimensional brownian motion which is invariant under the quantum groups u n of woronowicz with v2

the levy ito decomposition in free probability in this paper we prove the free analog of the levy ito decomposition for levy processes a significant part of the proof consists of introducing free poisson random measures proving their existence and developing a theory of integration with respect to such measures the existence of free poisson random measures also yields via the free levy ito decomposition an alternative proof of the general existence of free levy processes in law

superconvergence to the central limit and failure of the cramer theorem for free random variables we show that convergence of the semicircle law in the free central limit theorem for bounded random variables is much better than expected thus the distributions which tend to the semicircle become absolutely continuous in finite time and the densities converge in a very strong sense we also show that the semicircle law is the free convolution of laws which are not semicircular thus proving that cramer s classical result for the normal distribution does not have a free counterpart

trade off between curvature tuning and position invariance in visual area v4 humans can rapidly recognize a multitude of objects despite differences in their appearance the neural mechanisms that endow high level sensory neurons with both selectivity to complex stimulus features and tolerance or invariance to identity preserving transformations such as spatial translation remain poorly understood previous studies have demonstrated that both tolerance and selectivity to conjunctions of features are increased at successive stages of the ventral visual stream that mediates visual recognition within a given area such as visual area v4 or the inferotemporal cortex tolerance has been found to be inversely related to the sparseness of neural responses which in turn was positively correlated with conjunction selectivity however the direct relationship between tolerance and conjunction selectivity has been difficult to establish with different studies reporting either an inverse or no significant relationship to resolve this we measured v4 responses to natural scenes and using recently developed statistical techniques we estimated both the relevant stimulus features and the range of translation invariance for each neuron focusing the analysis on tuning to curvature a tractable example of conjunction selectivity we found that neurons that were tuned to more curved contours had smaller ranges of position invariance and produced sparser responses to natural stimuli these trade offs provide empirical support for recent theories of how the visual system estimates 3d shapes from shading and texture flows as well as the tiling hypothesis of the visual space for different curvature values

characterizing responses of translation invariant neurons to natural stimuli maximally informative invariant dimensions the human visual system is capable of recognizing complex objects even when their appearances change drastically under various viewing conditions especially in the higher cortical areas the sensory neurons reflect such functional capacity in their selectivity for complex visual features and invariance to certain object transformations such as image translation due to the strong nonlinearities necessary to achieve both the selectivity and invariance characterizing and predicting the response patterns of these neurons represents a formidable computational challenge a related problem is that such neurons are poorly driven by randomized inputs such as white noise and respond strongly only to stimuli with complex high order correlations such as natural stimuli here we describe a novel two step optimization technique that can characterize both the shape selectivity and the range and coarseness of position invariance from neural responses to natural stimuli one step in the optimization is finding the template as the maximally informative dimension given the estimated spatial location where the response could have been triggered within each image the estimates of the locations that triggered the response are updated in the next step under the assumption of a monotonic relationship between the firing rate and stimulus projections on the template at a given position the most likely location is the one that has the largest projection on the estimate of the template the algorithm shows quick convergence during optimization and the estimation results are reliable even in the regime of small signal to noise ratios when we apply the algorithm to responses of complex cells in the primary visual cortex v1 to natural movies we find that responses of the majority of cells were significantly better described by translation invariant models based on one template compared with position specific models with several relevant features

wick product for commutation relations connected with yang baxter operators and new constructions of factors we analyze a certain class of von neumann algebras generated by selfadjoint elements for satisfying the general commutation relations such algebras can be continuously embedded into some closure of the set of finite linear combinations of vectors where is an orthonormal basis of a hilbert space the operator which represents the vector is denoted by and called the wick product of the operators we describe explicitly the form of this product also we estimate the operator norm of for finally we apply these two results and prove that under the assumption all the von neumann algebras considered are ii 1 factors

noncommutative levy processes for generalized particularly anyon statistics let t mathbb r d let a function qt 2 to mathbb c satisfy q s t overline q t s and q s t 1 a generalized statistics is described by creation operators partial t dagger and annihilation operators t t in t which satisfy the q commutation relations partial s partial dagger t q s t partial dagger t partial s delta s t partial s partial t q t s partial t partial s partial dagger s partial dagger t q t s partial dagger t partial dagger s from the point of view of physics the most important case of a generalized statistics is the anyon statistics for which q s t is equal to q if s t here q in mathbb c q 1 we start the paper with a detailed discussion of a q fock space and operators partial t dagger partial t t in t in it which satisfy the q commutation relations next we consider a noncommutative stochastic process white noise omega t partial t dagger partial t lambda partial t dagger partial t t in t here lambda in mathbb r is a fixed parameter the case 0 corresponds to a q analog of brownian motion while 0 corresponds to a centered q poisson process we study q hermite q charlier respectively polynomials of infinitely many noncommutatative variables omega t t in t the main aim of the paper is to explain the notion of independence for a generalized statistics and to derive corresponding levy processes to this end we recursively define q cumulants of a field xi t t in t this allows us to define a q levy process as a field xi t t in t whose values at different points of t are q independent and which possesses a stationarity of increments in a certain sense we present an explicit construction of a q levy process and derive a nualart schoutens type chaotic decomposition for such a process

q gaussian processes non commutative and classical aspects we examine for 1 q 1 q gaussian processes i e families of operators non commutative random variables where the a t fulfill the q commutation relations for some covariance function equipped with the vacuum expectation state we show that there is a q analogue of the gaussian functor of second quantization behind these processes and that this structure can be used to translate questions on q gaussian processes into corresponding and much simpler questions in the underlying hilbert space in particular we use this idea to show that a large class of q gaussian processes possesses a non commutative kind of markov property which ensures that there exist classical versions of these non commutative processes this answers an old question of frisch and bourret fb

comparison of information and variance maximization strategies for characterizing neural feature selectivity this paper compares several statistical methods for analyzing neural feature selectivity with natural stimuli despite the non gaussian character of correlations in natural stimuli several relevant stimulus dimensions can be found by maximizing either information or as is demonstrated here variance in the case of information the relevance of each dimension is quantified by a kullback leibler divergence between the full input probability distribution and that across inputs associated with positive neural responses both projected onto that dimension we demonstrate that least square matching of the nonlinear prediction based on several dimensions relevant to the recorded spike trains yields an optimization scheme similar to information maximization the relevant dimensions are found as those that capture the most variance in neural response the variance along a stimulus dimension is given by a renyi divergence of order 2 instead of the kullback leibler divergence used for maximizing information statistical errors expected for the two schemes are shown to be similar through both analytical and numerical calculations however in the asymptotic limit of large spike numbers maximizing information results in smaller errors than variance optimization numerical simulations for model cells with different noise levels show that this trend persists and possibly increases when the number of spikes decreases this makes the problem of finding relevant dimensions one of the examples where information theoretic approaches are no more data limited than the variance based measures variance and information optimization also outperform methods based on the spike triggered average for all numbers of spikes and neural noise levels

riesz transforms on deformed fock spaces the fock von neumann algebra equipped with its canonical trace is spanned by n hermitian operators acting on a hilbert fock space some commutation relations between and are defined by the n n hermitian matrix a we define a riesz transform where is the number operator is aninner derivation unbounded in general and let 1 p we prove that is equivalent to for every with null trace with constants which do not depend on n

generalised brownian motion and second quantisation a new approach to the generalised brownian motion introduced by m bouzejko and r speicher is described based on symmetry rather than deformation the symmetrisation principle is provided by joyal s notions of tensorial and combinatorial species any such species v gives rise to an endofunctor fv of the category of hilbert spaces with contractions a generalised brownian motion is an algebra of creation and annihilation operators acting on fv h for arbitrary hilbert spaces h and having a prescription for the calculation of vacuum expectations in terms of a function t on pair partitions the positivity is encoded by a semigroup of broken pair partitions whose representation space with respect to t is v the existence of the second quantisation as functor t from hilbert spaces to noncommutative probability spaces is proved to be equivalent to the multiplicative property of the function t for a certain one parameter interpolation between the fermionic and the free brownian motion it is shown that the field algebras k are type ii1 factors when k is infinite dimensional

construction of quantum field theories with factorizing s matrices the subject of this thesis is a novel construction method for interacting relativistic quantum field theories on two dimensional minkowski space employing the algebraic framework of quantum field theory it is shown under which conditions an algebra of observables localized in a wedge shaped region of spacetime can be used to construct model theories a crucial input in this context is the modular nuclearity condition for wedge algebras which implies the existence of local observables as an application of the new method a rigorous construction of a large family of models with factorizing s matrices is obtained in an inverse scattering approach a given factorizing scattering operator is used to define certain semi localized wightman fields associated to it with the help of these fields a wedge algebra can be defined which determines the local observable content of a well defined quantum field theory in this approach the modular nuclearity condition translates to certain analyticity and boundedness conditions on the formfactors of wedge local observables these conditions are shown to hold for a large class of underlying s matrices including the scattering operators of the sinh gordon model and the scaling ising model as special examples the so constructed models are investigated with respect to their scattering properties they are shown to solve the inverse scattering problem for the underlying s matrices and a proof of asymptotic completeness for these models is given

analyzing neural responses to natural signals maximally informative dimensions we propose a method that allows for a rigorous statistical analysis of neural responses to natural stimuli that are nongaussian and exhibit strong correlations we have in mind a model in which neurons are selective for a small number of stimulus dimensions out of a high dimensional stimulus space but within this subspace the responses can be arbitrarily nonlinear existing analysis methods are based on correlation functions between stimuli and responses but these methods are guaranteed to work only in the case of gaussian stimulus ensembles as an alternative to correlation functions we maximize the mutual information between the neural responses and projections of the stimulus onto low dimensional subspaces the procedure can be done iteratively by increasing the dimensionality of this subspace those dimensions that allow the recovery of all of the information between spikes and the full unprojected stimuli describe the relevant subspace if the dimensionality of the relevant subspace indeed is small it becomes feasible to map the neuron s input output function even under fully natural stimulus conditions these ideas are illustrated in simulations on model visual and auditory neurons responding to natural scenes and sounds respectively

freeness of linear and quadratic forms in von neumann algebras we characterize the semicircular distribution by freeness of linear and quadratic forms in noncommutative random variables from tracial w probability spaces with relaxed moment conditions

r transforms of free joint distributions and non crossing partitions abstract we introduce an extension of the notion of r transform defined by d voiculescu to free joint distributions i e normalized linear functionals on algebras of non commutative polynomials in several indeterminates we point out that the r transform has good behavior with respect to the operations of free product and free convolution of joint distributions we prove that the explicit computation of the inverse r transform of a joint distribution is done via a formula of summation over the lattice of non crossing partitions which shows that the r transform is the operator theoretic counterpart of the free cumulants considered in the combinatorial approach of r speicher moreover in connection to the equivariance of the multidimensional r transform under rotations we show that a natural free analogue of a classical result about rotations of independent random variables is holding

cumulants in noncommutative probability theory i noncommutative exchangeability systems cumulants linearize convolution of measures we use a formula of good to define noncommutative cumulants in a very general setting it turns out that the essential property needed is exchangeability of random variables roughly speaking the formula says that cumulants are moments of a certain discrete fourier transform of a random variable this provides a simple unified method to understand the known examples of cumulants like classical free and various q cumulants

operator khintchine inequality in non commutative probability abstract for the operator t sum n k 1 a k otimes r k where a k belongs to the schatten class s 2n and where r k are non commutative random variables with mixed moments satisfying a specific condition we prove the following khintchine inequality vert t vert 2n leq d 2n left left vert left sum n k001 a ka k right frac 1 2 right vert s 2n quad quad left vert left sum n k 1 a k a k right frac 1 2 right vert s 2n right we find the optimal constants d 2n in the case when r k are the q gaussian and circular random variables moreover we show that the moments of any probability symmetric measure appear as the optimal constants for some random variables

on a class of free levy laws related to a regression problem abstract the free meixner laws arise as the distributions of orthogonal polynomials with constant coefficient recursions we show that these are the laws of the free pairs of random variables which have linear regressions and quadratic conditional variances when conditioned with respect to their sum we apply this result to describe free levy processes with quadratic conditional variances and to prove a converse implication related to asymptotic freeness of random wishart matrices

contractivity properties of ornstein uhlenbeck semigroup for general commutation relations we study a certain class of von neumann algebras generated by selfadjoint elements i a i a i where a i a i satisfy the general commutation relations

fock space associated to coxeter groups of type b abstract in this article we construct a generalized gaussian process coming from coxeter groups of type b it is given by creation and annihilation operators on an q fock space which satisfy the commutation relation b q x b q y q b q y b q x x y i x y q 2 n where x y are elements of a complex hilbert space with a self adjoint involution x x and n is the number operator with respect to the grading on the q fock space we give an estimate of the norms of creation operators we show that the distribution of the operators b q x b q x with respect to the vacuum expectation becomes a generalized gaussian distribution in the sense that all mixed moments can be calculated from the second moments with the help of a combinatorial formula related with set partitions our generalized gaussian distribution is associated to the orthogonal polynomials called the q meixner pollaczek polynomials yielding the q hermite polynomials when 0 and free meixner polynomials when q 0

de finetti theorem on the car algebra the symmetric states on a quasi local c algebra on the infinite set of indices j are those invariant under the action of the group of the permutations moving only a finite but arbitrary number of elements of j the celebrated de finetti theorem describes the structure of the symmetric states i e exchangeable probability measures in classical probability in the present paper we extend the de finetti theorem to the case of the car algebra that is for physical systems describing fermions namely after showing that a symmetric state is automatically even under the natural action of the parity automorphism we prove that the compact convex set of such states is a choquet simplex whose extremal i e ergodic w r t the action of the group of permutations previously described are precisely the product states in the sense of araki moriya in order to do that we also prove some ergodic properties naturally enjoyed by the symmetric states which have a self containing interest

cumulants in noncommutative probability theory ii we continue the investigation of noncommutative cumulants in this paper various characterizations of generalized gaussian random variables are proved

fock representations of quantum fields with generalized statistics we develop a rigorous framework for constructing fock representations of quantum fields obeying generalized statistics the main features of these representations are investigated various aspects of the underlying mathematical structure are illustrated by means of explicit examples

adapting for the missing link we consider the fitting of generalized linear models in wich the link function is assumed to be unknown and propose the following computational method first estimate regression coefficients using the canonical link then estimate the link via a kernel smoother treating the direction in the predictor space determined by the regression coefficients as known then reestimate the direction using the estimated link and alternate between these two steps we show that under fairly general conditions n 1 2 consistent estimates of the direction are obtained a small monte carlo study is presented

sample variance in free probability abstract let x 1 x 2 x n denote i i d centered standard normal random variables then the law of the sample variance q n i 1 n x i x 2 is the 2 distribution with n 1 degrees of freedom it is an open problem in classical probability to characterize all distributions with this property and in particular whether it characterizes the normal law in this paper we present a solution of the free analogue of this question and show that the only distributions whose free sample variance is distributed according to a free 2 distribution are the semicircle law and more generally so called odd laws by which we mean laws with vanishing higher order even cumulants in the way of proof we derive an explicit formula for the free cumulants of q n which shows that indeed the odd cumulants do not contribute and which exhibits an interesting connection to the concept of r cyclicity

a noncommutative extended de finetti theorem abstract the extended de finetti theorem characterizes exchangeable infinite sequences of random variables as conditionally i i d and shows that the apparently weaker distributional symmetry of spreadability is equivalent to exchangeability our main result is a noncommutative version of this theorem in contrast to the classical result of ryll nardzewski exchangeability turns out to be stronger than spreadability for infinite sequences of noncommutative random variables out of our investigations emerges noncommutative conditional independence in terms of a von neumann algebraic structure closely related to popa s notion of commuting squares and kummerer s generalized bernoulli shifts our main result is applicable to classical probability quantum probability in particular free probability braid group representations and jones subfactors

multiplicative functions on the lattice of non crossing partitions and free convolution the lattice of non crossing partitions was introduced by kreweras kre in 1972 and examined further by poupard pou and edelman edel ede2 in the last time there has been an increased interest in this lattice on one hand from the purely combinatorial point of view siu eds sire bss and on the other hand from a quantum probabilistic point of view gss spel spe2 spe3 we became interested in this lattice when we noticed that it is connected with some new form of convolution for probability measures the free convolution introduced by voiculescu voil voi2 voi3 this connection between the free convolution and the lattice of non crossing partitions is exactly analogous to the connection between the usual convolution and the lattice of all partitions we shall work out this connection in the last part of this work the intention of this article is to show that both the purely combinatorial and the probabilistic point of view can benefit from each other motivated by voiculescu s formula for the r series of free convolution we examine multiplicative functions on the lattice of non crossing partitions and prove our main theorem which is much in the spirit of voiculescu s formula we shall then use this main theorem for deriving some known results on non crossing partitions in a unified way this part of our work is purely combinatorial the free convolution serves only as a motivation for our theorem in the last section we shall switch to the probabilistie side and show how the lattice of non crossing partitions determines the structure of the free convolution voiculescu s formula will then follow as an easy corollary of our main theorem in this respect we shall get a purely combinatorial proof of this formula without any operator algebraic or functional analytic tools