Regular orbits in powers of permutation representations

Let (Q,G) be a faithful permutation representation of a finite group G. Suppose that the G-set Q has t distinct non-zero marks. In a permutation representation analogue of a theorem of Brauer on linear representations, it is shown that the direct power (Q,G)^t of (Q,G) contains a regular orbit. As a corollary, the probability that a random element of Q^r lies in a regular orbit of (Q,G)^r is shown to tend to 1 exponentially fast as r tends to \infin\infin. Further, knowledge of the rate of convergence is equivalent to knowledge of the second largest value of the character of the linear permutation representation.     

Field of definition and Galois orbits for the Macbeath-Hurwitz curves

Hurwitz curves are Riemann surfaces with 84(g-1) automorphisms, g the genus. Defined over some number field they permit an obvious Gal ([`(\Bbb Q)]/\Bbb Q){\rm Gal} (\overline {{\Bbb Q}}/{\Bbb Q}) action. We investigate this action for the first known infinite series of Hurwitz curves, due to Macbeath, using the canonical model of the curves. As a result we obtain the minimal field of definition for these curves. The method can be extended to some other infinite series of modular curves for non-congruence subgroups.     

On the singularities of residual intertwining operators

Let G be a reductive algebraic group defined over \Bbb Q {\Bbb Q} . Let P, P' be parabolic subgroups of G, defined over \Bbb Q {\Bbb Q} , and let _boxclose_boxclose, a_P') t \in W({\frak a}_{P}, {\frak a}_{P'}) . In this paper we study the intertwining operator M_P￠|P(t,l), l ? \frak a^*_{P,\Bbb C} M_{P' \vert P}(t,\lambda),\,\lambda \in {\frak a}^*_{P,{\Bbb C}} , acting in corresponding spaces of automorphic forms. One of the main results states that each matrix coefficient of M_P￠|P(t,l) M_{P' \vert P}(t,\lambda) is a meromorphic function of order ￡ n + 1 \le n + 1 , where n = dim G. Using this result, we further investigate the rank one intertwining operators, in particular, we study the distribution of their poles.     

(2, 3, k)-generated groups of large rank

For any fixed k 3 7k \geq 7 there exist integers n_k and a_k such that if the ring R is generated by a set of m elements t₁,...,t_m, where 2t₁-t₁²2t_1-t_1^2 is a unit of finite multiplicative order, and n 3 n_k+ma_kn \geq n_k+ma_k, then the group E_n(R) generated by elementary transvections is an epimorphic image of the triangle group D(2,3,k).\Delta (2,3,k).     

On the moduli spaces of fiber bundles of curves of genus $\geqq 2$

We determine the moduli spaces parametrizing analytic fiber bundles of curves of genus g \geqq 2g \geqq 2 over curves of genus g_b > (g + 1)/2.     

On the spectral mapping theorem for perturbed strongly continuous semigroups

We consider a strongly continuous semigroup (T(t))_{t \geqq 0}(T(t))_{t \geqq 0} with generator A on a Banach space X, an A-bounded perturbation B, and the semigroup (S(t))_{t \geqq 0}(S(t))_{t \geqq 0} generated by A + B. Using the critical spectrum introduced recently, we improve existing spectral mapping theorems for the perturbed semigroup (S(t))_{t \geqq 0}(S(t))_{t \geqq 0} .     

A wavelike functional equation of Pexider type

Summary. Let (G, +) and (H, +) be abelian groups such that the equation 2u = v 2u = v is solvable in both G and H. It is shown that if f₁, f₂, f₃, f₄, : G ×G ? H f_1, f_2, f_3, f_4, : G \times G \longrightarrow H satisfy the functional equation f₁(x + t, y + s) + f₂(x - t, y - s) = f₃(x + s, y - t) + f₄(x - s, y + t) for all x, y, s, t ? G x, y, s, t \in G , then f₁, f₂, f₃, and f₄ are given by f₁ = w + h, f₂ = w - h, f₃ = w + k, f₄ = w - k where w : G ×G ? H w : G \times G \longrightarrow H is an arbitrary solution of f (x + t, y + s) + f (x - t, y - s) = f (x + s, y - t) + f (x - s, y + t) for all x, y, s, t ? G x, y, s, t \in G , and h, k : G ×G ? H h, k : G \times G \longrightarrow H are arbitrary solutions of D_y,t³g(x,y) = 0 \Delta_{y,t}^{3}g(x,y) = 0 and D_x,t³g(x,y) = 0 \Delta_{x,t}^{3}g(x,y) = 0 for all x, y, s, t ? G x, y, s, t \in G .     

A note on discrete heat conduction

If the longitudinal line method is applied to the Cauchy problem u_t = u_xx, u(0, x) = u₀(x) with a bounded function u₀, one is led to a linear initial value problem v￠(t)=A v(t), v(0)=wv'(t)=A v(t),\, v(0)=w in l^￥ (\Bbb Z)l^\infty (\Bbb Z). Using Banach limit techniques we study the asymptotic behaviour of the solutions of these problems as t tends to infinity.     

The determination of the thermal properties of a heat conductor in a nonlinear heat conduction problem

This paper considers the inverse determination of the positive unknown thermal properties K(T), C(T) and the unknown temperature T(_{x, t}) in the nonlinear transient heat conduction equation. In addition to prescribed initial and/or boundary values, specified continuously differentiable temperature data T(x₀, t) with non-zero derivative at a single sensor location x = x₀ is given. When K(T) and C(T) obey a certain relationship which enables one to linearise exactly the nonlinear heat equation then their dependence upon T is obtained explicitly, whilst the unknown temperature T(x, t) is obtained implicitly and is then calculated numerically. Results are presented and discussed for infinite, semi-infinite and finite slabs.     

Funktionen, deren Maxima eine asymptotisch konstante Folge bilden

Es sei M₁ die Klasse der reellwertigen Funktionen f derart, daß lim_{tk? ￥} |f(t_k)| = c\lim \limits _{t_k\to \infty } |f(t_k)| = c gilt, wobei |f(t_k)||f(t_k)| die lokalen Maxima von | f | und c = c (f) eine positive Konstante ist. Diese Klasse tritt häufig im Zusammenhang mit Differentialgleichungen auf und ist kürzlich Gegenstand von mehreren Arbeiten geworden. Oft gelingt es, nur mf ? M₁mf \in M_1 mit einer passenden Funktion m ~ 1m\sim 1 zu zeigen, und es erhebt sich die Frage, ob daraus f ? M₁f \in M_1 folgt. Diese Frage wird hier für eine Unterklasse M ì M₁M \subset M_1 untersucht. Unsere Ergebnisse füllen eine Lücke in früheren Arbeiten und sind unserer Meinung nach auch für sich selbst von Interesse.     

On the equivariant structure of ideals in abelian extensions of local fields (with an appendix by W. Bley)

Let p be an odd rational prime and K a finite extension of \Bbb Q_p {\Bbb Q}_p . We give a complete classification of those finite abelian extensions L/K L/K in which any ideal of the valuation ring of L is free over its associated order in \Bbb Q_p[Gal(L/K)] {\Bbb Q}_p[Gal(L/K)] . In an appendix W. Bley describes an algorithm which can be used to determine the structure of Galois stable ideals in abelian extensions of number fields. The algorithm is applied to give several new and interesting examples.     

The Problem of Freeness for Euler Monoids and Möbius Groups

The Euler monoid E_n = {(a,b,t) epsilon Z³ : a² + b² = tⁿ, n S 1, is free if and only if n is odd (Theorem 1). We extend the results of Lyndon and Ullman, and Beardon concerning the set of those rational numbers mu epsilon (-2,2) for which the matrix Möbius group G_mu generated by A= and B = is not free (Theorems 2, 3, 4).     

Complex Angular Momentum Diagonalization of the Bethe-Salpeter Structure in General Quantum Field Theory

The Complex Angular Momentum (CAM) representation of (scalar) fourpoint functions has been previously established starting from the general principles of local relativistic Quantum Field Theory (QFT). Here, we carry out the diagonalization of the general t-channel Bethe-Salpeter (BS) structure of four-point functions in the corresponding CAM variable 5^t, for all negative values of the squared-energy variable t. This diagonalization is closely related to the existence of BS-equations for the absorptive parts in the crossed channels, interpreted as convolution equations with spectral properties. The production of Regge poles equipped with factorized residues involving Euclidean three-point functions appears as conceptually built-in in the analytic axiomatic framework of QFT. The existence of leading Reggeon terms governing the asymptotic behaviour of the four-point function at fixed t is strictly conditioned by the asymptotic behaviour of a g lobal Bethe-Salpeter kernel of the theory.     

Embeddings of non-commutative Lp-spaces into non-commutative L1-spaces, 1 < p < 2

It will be shown that for 1 < p < 2 the Schatten p-class is isometrically isomorphic to a subspace of the predual of a von Neumann algebra. Similar results hold for non-commutative L_p(N, t) L_p(N, \tau) -spaces defined by a finite trace on a finite von Neumann algebra. The embeddings rely on a suitable notion of p-stable processes in the non-commutative setting.     

Two-dimensional complex tori with multiplication by $\sqrt {d}$

We give an elementary argument for the well known fact that the endomorphism algebra End(A)?\Bbb Q {\rm {End}}(A)\otimes {\Bbb Q } of a simple complex abelian surface A can neither be an imaginary quadratic field nor a definite quaternion algebra. Another consequence of our argument is that a two-dimensional complex torus T with \Bbb Q (?d)\hookrightarrow End_{\Bbb Q} (T){\Bbb Q }(\sqrt {d})\hookrightarrow {\rm{End_{{\Bbb Q }}}}(T) where \Bbb Q (?d){\Bbb Q }(\sqrt {d}) is real quadratic, is algebraic.     

More on quotient polytopes

Summary. In an earlier paper, it was shown that every abstract polytope is a quotient Q = M(W)/N {\cal Q} = {\cal M}(W)/N of some regular polytope M(W) {\cal M}(W) whose automorphism group is W, by a subgroup N of W. In this paper, attention is focussed on the quotient Q {\cal Q} , and various important structures relating to polytopes are described in terms of N ', the stabilizer of a flag of the quotient under an action of W (the 'flag action'). It is pointed out how N ' may be assumed without loss of generality to equal N. The paper also shows what properties of N ' yield polytopes which are regular, section regular, chiral, locally regular, or locally universal. The aim is to make it more practical to study non-regular polytopes in terms of group theory.     

Complex finitary simple Lie algebras

An algebra is called finitary if it consists of finite-rank transformations of a vector space. We classify finitary simple Lie algebras over an algebraically closed field of zero characteristic. It is shown that any such algebra is isomorphic to one of the following¶ (1) a special transvection algebra \frak t(V,P)\frak t(V,\mit\Pi );¶ (2) a finitary orthogonal algebra \frak fso (V,q)\frak {fso} (V,q); ¶ (3) a finitary symplectic algebra \frak fsp (V,s)\frak {fsp} (V,s).¶Here V is an infinite dimensional K-space; q (respectively, s) is a symmetric (respectively, skew-symmetric) nondegenerate bilinear form on V; and P\Pi is a subspace of the dual V^* whose annihilator in V is trivial: 0={v ? V | Pv=0}0=\{{v}\in V\mid \Pi {v}=0\}.     

On the mean lattice point discrepancy of a convex disc

For a convex planar domain D \cal {D} , with smooth boundary of finite nonzero curvature, we consider the number of lattice points in the linearly dilated domain t D t \cal {D} . In particular the lattice point discrepancy P_D(t) P_{\cal {D}}(t) (number of lattice points minus area), is investigated in mean-square over short intervals. We establish an asymptotic formula for¶¶ ò_{T - L}^{T + L}(P_D(t))²dt \int\limits_{T - \Lambda}^{T + \Lambda}(P_{\cal {D}}(t))^2\textrm{d}t ,¶¶ for any L = L(T) \Lambda = \Lambda(T) growing faster than logT.     

Restricted 1-3-2 Permutations and Generalized Patterns

Recently, Babson and Steingrimsson (see [2]) introduced generalized permutations patterns that allow the requirement that two adjacent letters in a pattern must be adjacent in the permutation. We study generating functions for the number of permutations on n letters avoiding 1-3-2 (or containing 1-3-2 exactly once) and an arbitrary generalized pattern t \tau on k letters, or containing t \tau exactly once. In several cases, the generating function depends only on k and can be expressed via Chebyshev polynomials of the second kind, and the generating function of Motzkin numbers.     

Nonsurjective epimorphisms in decomposable varieties

We characterize when a subgroup H of a group G is epimorphically embedded in G in a varietal product NQ \mathcal{NQ} , in terms of the epimorphisms in N \mathcal{N} and the laws of Q \mathcal{Q} . This reduces the characterization of nonsurjective epimorphisms to the indecomposable varieties. We also prove that the existence of an epimorphically embedded proper subgroup of a simple group in N \mathcal{N} implies the existence of a nonsurjective epimorphism in any varietal product NQ \mathcal{NQ} , provided that Q \mathcal{Q} is not the variety of all groups.