Concatenating Variational Principles and the Kinetic Stress-Energy-Momentum Tensor
We show how to "concatenate" variational principles over dierent 
bases into one over a single base, thereby providing a unied Lagrangian 
treatment of interacting systems. As an example we study a Klein{ 
Gordon eld interacting with a mesically charged particle. We employ 
our method to give a novel group-theoretic derivation of the kinetic 
stress-energy-momentum tensor density corresponding to the particle.
Stress-Energy-Momentum Tensors and the Belinfante-Rosenfeld Formula
We present a new method of constructing a stress-energy-momentum tensor 
for a classical field theory based on covariance considerations and Noether theory. 
The stress-energy-momentum tensor T ^μ 
_ν that we construct is defined using 
the (multi)momentum map associated to the spacetime diffeomorphism group. 
The tensor T ^μ 
_ν is uniquely determined as well as gauge-covariant, and depends 
only upon the divergence equivalence class of the Lagrangian. It satisfies 
a generalized version of the classical Belinfante-Rosenfeld formula, and hence 
naturally incorporates both the canonical stress-energy-momentum tensor and 
the “correction terms” that are necessary to make the latter well behaved. Furthermore, 
in the presence of a metric on spacetime, our T^(μν) coincides with the 
Hilbert tensor and hence is automatically symmetric.
How to do a p-descent on an elliptic curve
In this paper, we describe an algorithm that reduces the computation of the (full) p-Selmer group of an elliptic curve E over a number field to standard number field computations such as determining the (p-torsion of) the S-class group and a basis of the S-units modulo pth powers for a suitable set S of primes. In particular, we give a result reducing this set S of 'bad primes' to a very small set, which in many cases only contains the primes above p. As of today, this provides a feasible algorithm for performing a full 3-descent on an elliptic curve over Q, but the range of our algorithm will certainly be enlarged by future improvements in computational algebraic number theory. When the Galois module structure of E[p] is favorable, simplifications are possible and p-descents for larger p are accessible even today. To demonstrate how the method works, several worked examples are included.