We obtain a necessary and sufficient condition for the linear independence of solutions of differential equations for hyperlogarithms. The key fact is that the multiplier (i.e. the factor $M$ in the differential equation $dS=MS$) has only singulariti
es of first order (Fuchsian-type equations) and this implies that they freely span a space which contains no primitive. We give direct applications where we extend the property of linear independence to the largest known ring of coefficients.
We show that the combinatorial numbers known as {em Bell numbers} are generic in quantum physics. This is because they arise in the procedure known as {em Normal ordering} of bosons, a procedure which is involved in the evaluation of quantum function
s such as the canonical partition function of quantum statistical physics, {it inter alia}. In fact, we shall show that an evaluation of the non-interacting partition function for a single boson system is identical to integrating the {em exponential generating function} of the Bell numbers, which is a device for encapsulating a combinatorial sequence in a single function. We then introduce a remarkable equality, the Dobinski relation, and use it to indicate why renormalisation is necessary in even the simplest of perturbation expansions for a partition function. Finally we introduce a global algebraic description of this simple model, giving a Hopf algebra, which provides a starting point for extensions to more complex physical systems.
We extend the Hopf algebra description of a simple quantum system given previously, to a more elaborate Hopf algebra, which is rich enough to encompass that related to a description of perturbative quantum field theory (pQFT). This provides a {em mat
hematical} route from an algebraic description of non-relativistic, non-field theoretic quantum statistical mechanics to one of relativistic quantum field theory. Such a description necessarily involves treating the algebra of polyzeta functions, extensions of the Riemann Zeta function, since these occur naturally in pQFT. This provides a link between physics, algebra and number theory. As a by-product of this approach, we are led to indicate {it inter alia} a basis for concluding that the Euler gamma constant $gamma$ may be rational.
We construct a three-parameter deformation of the Hopf algebra $LDIAG$. This is the algebra that appears in an expansion in terms of Feynman-like diagrams of the {em product formula} in a simplified version of Quantum Field Theory. This new algebra i
s a true Hopf deformation which reduces to $LDIAG$ for some parameter values and to the algebra of Matrix Quasi-Symmetric Functions ($MQS$) for others, and thus relates $LDIAG$ to other Hopf algebras of contemporary physics. Moreover, there is an onto linear mapping preserving products from our algebra to the algebra of Euler-Zagier sums.
We construct a three parameter deformation of the Hopf algebra $mathbf{LDIAG}$. This new algebra is a true Hopf deformation which reduces to $mathbf{LDIAG}$ on one hand and to $mathbf{MQSym}$ on the other, relating $mathbf{LDIAG}$ to other Hopf algeb
ras of interest in contemporary physics. Further, its product law reproduces that of the algebra of polyzeta functions.
In a recent series of communications we have shown that the reordering problem of bosons leads to certain combinatorial structures. These structures may be associated with a certain graphical description. In this paper, we show that there is a Hopf A
lgebra structure associated with this problem which is, in a certain sense, unique.
