Physics Letters B 773 (2017) 625–631
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Physics Letters B
www.elsevier.com/locate/physletb
Relations between positivity, localization and degrees of freedom:
The Weinberg–Witten theorem and the van Dam–Veltman–Zakharov
discontinuity
Jens Mund
a
, Karl-Henning Rehren
b,∗
, Bert Schroer
c,d
a
Departamento de Física, Universidade Federal de Juiz de Fora, Juiz de Fora 36036-900, MG, Brazil
b
Institut für Theoretische Physik, Universität Göttingen, 37077 Göttingen, Germany
c
Centro Brasileiro de Pesquisas Físicas, 22290-180 Rio de Janeiro, RJ, Brazil
d
Institut für Theoretische Physik der FU Berlin, 14195 Berlin, Germany
a r t i c l e i n f o a b s t r a c t
Article history:
Received
27 March 2017
Received
in revised form 30 August 2017
Accepted
30 August 2017
Available
online 12 September 2017
Editor:
N. Lambert
The problem of accounting for the quantum degrees of freedom in passing from massive higher-spin
potentials to massless ones, and the inverse problem of “fattening” massless tensor potentials of helicity
±h to their massive s =
|
h
|
counterparts, are solved – in a perfectly ghost-free approach – using “string-
localized
fields”.
This
approach allows to overcome the Weinberg–Witten impediment against the existence of massless
|
h
|
≥
2 energy–momentum tensors, and to qualitatively and quantitatively resolve the van Dam–Veltman–
Zakharov
discontinuity concerning, e.g., very light gravitons, in the limit m → 0.
© 2017 The Author(s). 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
In relativistic quantum field theory, the quantization of interact-
ing
massless or massive classical potentials of higher spin (s ≥ 1)
either violates Hilbert space positivity which is an indispensable
attribute of the probability interpretation of quantum theory, or
leads to a violation of the power counting bound of renormaliz-
ability
whose maintenance requires again a violation of positivity.
In
order to save positivity for those quantum fields which cor-
respond
to classically gauge invariant observables, one usually for-
mally
extends the theory by adding degrees of freedom in the
form of negative metric Stückelberg fields and “ghosts” without
a counterpart in classical gauge theories. The justification for this
quantum gauge setting is that one can extract from the indefinite
metric Krein space a Hilbert space that the gauge invariant opera-
tors
generate from the vacuum.
This
situation is satisfactory as far as the vacuum sector and
the perturbative construction of a unitary gauge-invariant S-matrix
are concerned. However the theory remains incomplete in that it
provides no physical interpolating fields that mediate between the
*
Corresponding author.
E-mail
addresses: mund@fisica.ufjf.br (J. Mund),
rehren@theorie.physik.uni-goettingen.de (K.-H. Rehren), schroer@zedat.fu-berlin.de
(B. Schroer).
causal localization of the field theory and the analytic structure of
the S-matrix in terms of fields that connect charged states with the
vacuum. Expressed differently, gauge theory allows to compute the
perturbative S-matrix, but cannot construct its off-shell extension
on a Hilbert space.
There
are two famous results about the higher-spin massless
case. The first is the Weinberg–Witten theorem [24] which states
that for s ≥ 2, no point-localized stress-energy tensor exists such
that the Poincaré generators are moments of its zero-components.
This result also obstructs the semiclassical coupling of massless
higher-spin matter to gravity.
The
second is the DVZ observation due to van Dam and Velt-
man
[25] and to Zakharov [28], that in interacting models with
s ≥ 2, scattering amplitudes are discontinuous in the mass at
m = 0, i.e., the scattering of matter through exchange of mass-
less
gravitons (say) is significantly different from the scattering via
gravitons of a very small mass.
Both
problems can be addressed, without being plagued by
the positivity troubles of gauge theories, with the help of “string-
localized
quantum fields” defined in the physical Hilbert space.
The latter may be regarded as a fresh start to Mandelstam’s at-
tempts
[12] to reformulate gauge theories as full-fledged theories
in which all fields live on the Hilbert space of the field strength.
The new point of view was triggered by a new approach to Wign-
er’s
infinite-spin representation [17], that proved to be useful also
http://dx.doi.org/10.1016/j.physletb.2017.08.058
0370-2693/
© 2017 The Author(s). 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
.