Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Fermions and gravitational gyrotropy   In conventional general relativity without torsion, high-frequency
gravitational waves couple to the chiral number density of spin one-half
quanta: the polarization of the waves is rotated by $2\pi N_5 {\ell_{\rm
Pl}^2}$, where $N_5$ is the chiral column density and $\ell_{\rm Pl}$ is the
Planck length. This means that if a primordial distribution of gravitational
waves with E-E or B-B correlations passed through a chiral density of fermions
in the very early Universe, an E-B correlation will be generated. This in turn
will give rise to E-B and T-B correlations in the cosmic microwave background
(CMB). Less obviously but more primitively, the condition Albrecht called
"cosmic coherence" would be violated, changing the restrictions on the class of
admissible cosmological gravitational waves. This altered class of waves would,
generally speaking, probe earlier physics than do the conventional waves; their
effects on the CMB would be most pronounced for low ($\lesssim 100$)
multipoles. Rough estimates indicate that if the tensor-to-scalar ratio is less
than about $10^{-2}$, it will be hard to constrain a spatially homogeneous
primordial $N_5$ by present data.

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The categories of this paper are: mtrl-th
24
The categories of this paper are: dg-ga
11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio
29
The categories of this paper are: funct-an
0
The categories of this paper are: hep-ph
26
The categories of this paper are: bayes-an
30
The categories of this paper are: q-alg
19
The categories of this paper are: eess
18
The categories of this paper are: econ
9
The categories of this paper are: nlin
12
The categories of this paper are: nucl-th
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The categories of this paper are: physics
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The categories of this paper are: patt-sol
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The categories of this paper are: atom-ph
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The categories of this paper are: cmp-lg