Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nucleosynthesis in gamma-ray bursts outflows   It is shown that fusion of neutrons and protons to He-4 nuclei occurs in
gamma-ray burst outflows in a process similar to big-bang nucleosynthesis in
the early Universe. Only the surviving free neutrons can then decouple
kinematically from the charged fluid so that the multi-GeV neutrino signal
predicted from inelastic nuclear n-p collisions is significantly reduced. It is
also argued that a sizeable fraction of ultra-high energy cosmic rays
accelerated in gamma-ray bursts should be He-4 nuclei.

29
The categories of this paper are: funct-an
36
The categories of this paper are: cmp-lg
0
The categories of this paper are: hep-ph
20
The categories of this paper are: acc-phys
22
The categories of this paper are: chao-dyn
21
The categories of this paper are: adap-org
5
The categories of this paper are: gr-qc
23
The categories of this paper are: solv-int
28
The categories of this paper are: alg-geom
31
The categories of this paper are: ao-sci
7
The categories of this paper are: hep-th
24
The categories of this paper are: dg-ga
11
The categories of this paper are: hep-lat
4
The categories of this paper are: cond-mat
12
The categories of this paper are: nucl-th
3
The categories of this paper are: physics