Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Direct URCA process in neutron stars with strong magnetic fields   We calculate the emissivity for the direct URCA process in strongly
magnetized, degenerate matter in neutron stars, under $\beta $-equilibrium. We
show that, if the magnetic field is large enough for protons and electrons to
be confined to the ground Landau levels, the field-free threshold condition on
proton concentration no longer holds, and direct URCA reactions are open for an
arbitrary proton concentration. Direct URCA process leads to an early phase of
fast neutron star cooling. This circumstance allows us to constrain the initial
magnetic field inside observed pulsars.

7
The categories of this paper are: hep-th
33
The categories of this paper are: plasm-ph
13
The categories of this paper are: quant-ph
1
The categories of this paper are: cs
21
The categories of this paper are: adap-org
24
The categories of this paper are: dg-ga
10
The categories of this paper are: q-bio
19
The categories of this paper are: eess
37
The categories of this paper are: supr-con
2
The categories of this paper are: math
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
27
The categories of this paper are: comp-gas
4
The categories of this paper are: cond-mat
14
The categories of this paper are: math-ph
18
The categories of this paper are: econ