Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Superconductivity and Quantum Phase Transitions in Weak Itinerant
  Ferromagnets   It is argued that the phase transition in low-T_c clean itinerant
ferromagnets is generically of first order, due to correlation effects that
lead to a nonanalytic term in the free energy. A tricritical point separates
the line of first order transitions from Heisenberg critical behavior at higher
temperatures. Sufficiently strong quenched disorder suppresses the first order
transition via the appearance of a critical endpoint. A semi-quantitative
discussion is given in terms of recent experiments on MnSi and UGe_2. It is
then shown that the critical temperature for spin-triplet, p-wave
superconductivity mediated by spin fluctuations is generically much higher in a
Heisenberg ferromagnetic phase than in a paramagnetic one, due to the coupling
of magnons to the longitudinal magnetic susceptibility. This qualitatively
explains the phase diagram recently observed in UGe_2 and ZrZn_2.

29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
9
The categories of this paper are: nlin
2
The categories of this paper are: math
16
The categories of this paper are: stat
19
The categories of this paper are: eess
0
The categories of this paper are: hep-ph
11
The categories of this paper are: hep-lat
3
The categories of this paper are: physics
27
The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn
31
The categories of this paper are: ao-sci
8
The categories of this paper are: hep-ex
20
The categories of this paper are: acc-phys
21
The categories of this paper are: adap-org
7
The categories of this paper are: hep-th