Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Neutral Order Parameters in Metallic Criticality in d=2+1 from a Hairy
  Electron Star   We use holography to study the spontaneous condensation of a neutral order
parameter in a (2+1)-dimensional field theory at zero-temperature and finite
density, dual to the electron star background of Hartnoll and Tavanfar. An
appealing feature of this field theory is the emergence of an IR Lifshitz
fixed-point with a finite dynamical critical exponent $z$, which is due to the
strong interaction between critical bosonic degrees of freedom and a finite
density of fermions (metallic quantum criticality). We show that under some
circumstances the electron star background develops a neutral scalar hair whose
holographic interpretation is that the boundary field theory undergoes a
quantum phase transition, with a Berezinski-Kosterlitz-Thouless character, to a
phase with a neutral order parameter. Including the backreaction of the bulk
neutral scalar on the background, we argue that the two phases across the
quantum critical point have different $z$, a novelty that exists in certain
quantum phase transitions in condensed matter systems. We also analyze the
system at finite temperature and find that the phase transition becomes, as
expected, second-order. Embedding the neutral scalar into a higher form, a
variety of interesting phases could potentially be realized for the boundary
field theory. Examples which are of particular interest to condensed matter
physics include an antiferromagnetic phase where a vector condenses and break
the spin symmetry, a quadrupole nematic phase which involves the condensation
of a symmetric traceless tensor breaking rotational symmetry, or different
phases of a system with competing order parameters.

28
The categories of this paper are: alg-geom
5
The categories of this paper are: gr-qc
14
The categories of this paper are: math-ph
34
The categories of this paper are: chem-ph
29
The categories of this paper are: funct-an
31
The categories of this paper are: ao-sci
25
The categories of this paper are: patt-sol
13
The categories of this paper are: quant-ph
12
The categories of this paper are: nucl-th
26
The categories of this paper are: bayes-an
23
The categories of this paper are: solv-int
1
The categories of this paper are: cs
27
The categories of this paper are: comp-gas
17
The categories of this paper are: q-fin
36
The categories of this paper are: cmp-lg
24
The categories of this paper are: dg-ga