We study 3-point functions at finite temperature in the closed time path formalism. We give a general decomposition of the eight component tensor in terms of seven vertex functions. We derive a spectral representation for these seven functions in terms of two independent real spectral functions. We derive relationships between the seven functions and obtain a representation of the vertex tensor...

Preface A famous theorem by Frobenius in 1901 proves that if a group G contains a proper non trivial subgroup H such that H ∩ g −1 Hg = {1 G } for all g ∈ G \ H, then there exists a normal subgroup N such that G is the semidirect product of N and H. Groups with this property-the so called Frobenius groups-arise in a natural way as transitive permutation groups, but they can also be characterize...

Given a set P of n points in R, let d1 > d2 > . . . denote all distinct inter-point distances generated by point pairs in P . It was shown by Schur, Martini, Perles, and Kupitz that there is at most one d-dimensional regular simplex of edge length d1 whose every vertex belongs to P . We extend this result by showing that for any k the number of d-dimensional regular simplices of edge length dk ...

The density matrix renormalization group (DMRG) is a numerical method that optimizes a variational state expressed by a tensor product. We show that the ground state is not fully optimized as far as we use the standard finite system algorithm, that uses the block structure B • •B. This is because the tensors are not improved directly. We overcome this problem by using the simpler block structur...

We study n-point functions at finite temperature in the closed time path formalism. With the help of two basic column vectors and their dual partners we derive a compact decomposition of the time-ordered n-point functions with 2 components in terms of 2n−1 − 1 independent retarded/advanced n-point functions. This representation greatly simplifies calculations in the real-time formalism. PACS nu...

A one-point extension of an egglike inversive plane of order n exists if, and only if, n is 2 or 3. Hence there are no 4-(18,6,1) designs and no 4-(66,10,1) designs. An inversive plane of order n is a one-point extension of an affine plane of ordern, that is, a 3-(n + 1,n + 1,1) design. An ovoid of PG(3, q), q > 2, is a set of q2 + 1 points, no three collinear. An ovoid of PG(3, 2) is a set of ...

We consider point sets in the affine plane Fq where each Euclidean distance of two points is an element of Fq . These sets are called integral point sets and were originally defined in m-dimensional Euclidean spaces Em. We determine their maximal cardinality I(Fq , 2). For arbitrary commutative rings R instead of Fq or for further restrictions as no three points on a line or no four points on a...

where q~ is a c losed, convex func t ion def ined on R n, having values in ~ and S is a c losed, convex set in ~n. We write S for the op t ima l so lu t ion set o f (1), S : = arg minxes cb(x) and assume this set to be non-empty , in o rde r tha t a p ro jec t ion o p e r a t i o n on to this set is well def ined. In o rde r to s impl i fy our analysis , let us define , b ~ ( x ) := ¢~(x )+~, (...

We consider the calculations of three-point functions at nite temperature as they are usually performed in the literature. We show that as normally used, the Imaginary-Time and the Real Time nite temperature formalisms calculate expectation values of retarded and time ordered three point functions respectively. We also present a relation between these quantities that shows that they are not gen...

In this paper, a parameter uniform numerical method based on Shishkin mesh is suggested to solve a system of second order singularly perturbed differential equations with a turning point exhibiting boundary layers. It is assumed that both equations have a turning point at the same point. An appropriate piecewise uniform mesh is considered and a classical finite difference scheme is applied on t...