Physics Letters B 798 (2019) 134956
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
On unfolded off-shell formulation for higher-spin theory
N.G. Misuna
a,b,∗
a
I.E. Tamm Department of Theoretical Physics, Lebedev Physical Institute, Leninsky prospect 53, 119991, Moscow, Russia
b
Moscow Institute of Physics and Technology, Institutsky pereulok 9, 141701, Dolgoprudny, Moscow region, Russia
a r t i c l e i n f o a b s t r a c t
Article history:
Received
24 July 2019
Received
in revised form 12 September
2019
Accepted
16 September 2019
Available
online 23 September 2019
Editor:
M. Cveti
ˇ
c
We present an unfolded off-shell formulation for free massless higher-spin fields in 4d Minkowski space
in terms of spinorial variables. This system arises from the on-shell one by the addition of external
higher-spin currents, for which we find an unfolded description. Also we show that this off-shell system
can be interpreted as Schwinger–Dyson equations and restore two-point functions of higher-spin fields
this way.
© 2019 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
1. Introduction
Higher-spin (HS) gauge theory (for a review see e.g. [1,2]), de-
scribing
interactions of massless fields of all spins and possess-
ing
infinite gauge symmetry, is of great interest for high-energy
physics. Firstly, it is regarded as possible symmetric high-energy
phase of string theory [3], secondly, it provides an example of
weak-weak Ad S/CFT correspondence, being dual to different con-
formal
vectorial models according to Klebanov–Polyakov conjecture
[4]. Available formulation of HS theory represents a full nonlinear
system of classical equations of motion written in the so-called
unfolded form – Vasiliev equations [5,6]. Unfolded dynamics ap-
proach
is a first-order formalism, possessing a manifest coordinate-
independence
(due to exterior forms language) and allowing an
easy control of gauge symmetries of the theory. However, obtain-
ing
conventional field-theoretical information from the unfolded
formulation turns out to be a very nontrivial problem. Up to date
only cubic HS vertices were managed to be extracted from Vasiliev
equations and compared with Ad S/CFT predictions [7–12].
One
of the main problems of HS theory is the absence of a full
nonlinear action (see, however, [13]), that does not allow the use
of standard AdS/CFT techniques and the study of quantization is-
sue.
A general systematic method of classifying all gauge-invariant
functionals of unfolded system was proposed in [14]. It consists in
studying cohomologies of certain operator determined by unfolded
equations of the theory. In the case of an on-shell unfolded sys-
*
Correspondence to: I.E. Tamm Department of Theoretical Physics, Lebedev Phys-
ical
Institute, Leninsky prospect 53, 119991, Moscow, Russia.
E-mail
address: misuna@phystech.edu.
tem (i.e. when it contains dynamical equations on primary fields)
such functionals correspond to conserved charges. In the case of
an off-shell unfolded system (when unfolded equations represent
a set of constraints expressing descendants via primaries with pre-
scribed
gauge symmetries) these functionals can be considered as
potential actions.
Thus,
in order to proceed in the search for HS action, one
should find an off-shell completion of Vasiliev equations – an un-
folded
system with the same spectrum of primary fields, proper
gauge transformations laws, but without any dynamical equations.
Such off-shell construction, resulting from relaxing tracelesness
condition, for Vasiliev theory of totally symmetric bosonic HS fields
in arbitrary dimension [15]was presented in [16]. However, the
most elaborated is another version of Vasiliev system, namely,
4d theory formulated in terms of spinors, which in most cases
is the only one where practical computations are feasible. Here
traces are absent by construction, so the method of [16]is inap-
plicable.
In this paper we propose an alternative way to look for
off-shell completion for this theory, by coupling it to external cur-
rents.
Concretely, we present an off-shell completion of unfolded
spinorial system of free HS in 4d flat spacetime. One of the ad-
vantage
of the proposed approach is that it allows one to look for
quantum correlation functions via interpreting off-shell equations
as the Schwinger–Dyson ones. We illustrate this by finding two-
point
functions of HS fields from the off-shell system we built.
The
paper is organized as follows. In Section 2 we recall some
facts about unfolded dynamics approach and HS equations. In Sec-
tion 3 we
construct unfolded description of Fronsdal currents and
use it to find an off-shell completion of free HS equations. In 4
two-point
correlation functions of HS fields are evaluated from the
off-shell system of Section 3. In 5 we present our conclusions.
https://doi.org/10.1016/j.physletb.2019.134956
0370-2693/
© 2019 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.