Eur. Phys. J. C (2018) 78:1012
https://doi.org/10.1140/epjc/s10052-018-6497-2
Regular Article - Theoretical Physics
The emergence of flagpole and flag-dipole fermions in fluid/gravity
correspondence
P. Meert
1,a
, R. da Rocha
2,b
1
Center of Natural and Human Sciences, Federal University of ABC, Santo André, Brazil
2
Center of Mathematics, Computing and Cognition, Federal University of ABC, Santo André, Brazil
Received: 5 September 2018 / Accepted: 4 December 2018 / Published online: 13 December 2018
© The Author(s) 2018
Abstract The emergence of flagpole and flag-dipole sin-
gular spinor fields is explored, in the context of fermionic
sectors of fluid/gravity correspondence, arising from the
duality between the gravitino, in supergravity, and the
phonino, in supersymmetric hydrodynamics. Generalized
black branes, whose particular case consists of the AdS–
Schwarzschild black brane, are regarded. The correspon-
dence between hydrodynamic transport coefficients, and the
universal absorption cross sections of the generalized black
branes, is extended to fermionic sectors, including super-
sound diffusion constants. A free parameter, in the gener-
alized black brane solution, is shown to control the flipping
between regular and singular fermionic solutions of the equa-
tions of motion for the gravitino.
1 Introduction
Classical spinor fields were classified studying all the pos-
sibilities to evaluate their respective bilinear covariants that
either satisfy the Fierz identities or their generalizations. This
feature has introduced the Lounesto’s spinor field classifi-
cation into six classes of spinor fields, assuming the U(1)
gauge symmetry of quantum electrodynamics [1]. A sec-
ond quantized version of such a classification was intro-
duced in Ref. [2], where quantum spinors and their corre-
lators provided a setup for a second quantized classification.
Going further, encompassing SU(2)×U(1) gauge symmetry,
a new classification, embracing spinor field multiplets that
represent non-Abelian gauge fields, was lately introduced
in Ref. [3]. Recently, new classes of fermionic fields on 7-
manifolds were derived [4,5], regarding, in particular, the
AdS
5
×S
5
and AdS
4
×S
7
compactifications [6], also includ-
ing new fermionic solutions of M-theory compactifications
a
e-mail: pedro.meert@ufabc.edu.br
b
e-mail: roldao.rocha@ufabc.edu.br
with one supersymmetry [7]. These new classes emulate sin-
gular spinor fields on higher dimensions and more general
signatures. Hence, it is natural to further explore the role of
the spinor fields classifications in the fluid/gravity correspon-
dence setup.
The low-energy/low-momentum limit of the AdS/CFT
correspondence is also known as fluid/gravity correspon-
dence. In this regime, the field theory side is taken to be
an effective theory, hence, hydrodynamics [8]. On the other
hand, the compactification of higher dimensions leads the
gravitational theory to conventional General Relativity (GR),
although this gives some freedom to play with extensions of
GR and investigation of its dual theories. This fact has lead
to successful predictions of transport coefficients in strongly
coupled field theories, being the quark-gluon plasma [9]the
most famous example, but not the only one, also appear-
ing in other setups, like the graphene [10], superconductors
[11], and Fermi liquids [12]. One intriguing feature of this
duality is the so called KSS result [13,14], named after Kov-
tun, Son and Starinets, which states that the shear viscos-
ity to entropy density ratio is universal, in the sense that
its numerical value is the same for almost all known physi-
cal systems. One exception involve a highly complex frame-
work [15].
To lead the fluid/gravity correspondence – essentially
based on bosonic fields – further, one aims to include
fermionic modes into the description. To accomplish so, one
refers to supersymmetry in the bulk and analyzes its effect
in the boundary, describing supersymmetric hydrodynamics
[16]. This setup indeed leads to predictions [17–22] and the
quest which concerns us in this work is related to the prob-
lem of whether a quantity similar to the shear viscosity to
entropy ratio, associated to fermionic sectors, exists. In Ref.
[23] the sound diffusion constant was first calculated in a
supersymmetric holographic background and indicated that
this quantity is the obvious candidate for the task, which was
investigated and asserted later by [24].
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