Physics Letters B 734 (2014) 239–244
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Very special relativity and Lorentz violating theories
Jorge Alfaro
a
, Victor O. Rivelles
b
a
Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile
b
Instituto de Física, Universidade de São Paulo, C. Postal 66318, São Paulo, SP, Brazil
a r t i c l e i n f o a b s t r a c t
Article history:
Received
13 January 2014
Received
in revised form 16 May 2014
Accepted
22 May 2014
Available
online 2 June 2014
Editor: M.
Cveti
ˇ
c
Very special relativity (VSR) keeps the main features of special relativity but breaks rotational invariance.
We will show how VSR like terms which depend on a fixed null vector can be generated systematically.
We start with a formulation for a spinning particle which incorporates VSR. We then use this formulation
to derive the VSR modifications to the Maxwell equations. Next we consider VSR corrections to Thomas
precession. We start with the coupling of the spinning particle to the electromagnetic field adding a
gyromagnetic factor which gives rise to a magnetic moment. We then propose a spin vector in terms of
the spinning particle variables and show that it obeys the BMT equation. All this is generalized to the
VSR context and we find the VSR contributions to the BMT equation.
© 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/3.0/). Funded by SCOAP
3
.
1. Introduction
The standard model of particle physics is a well established and
experimentally confirmed theory but it needs to be extended in
order to incorporate some known phenomena like, for instance,
neutrino masses and dark matter. Possibly the standard model is
the low energy limit of a larger theory which hopefully includes
gravity. Since the present experimental data are not enough to
point out how to extend the standard model we must seek for
small deviations of it which could be detected at low energies. One
possibility is that fields from a more complete theory couple to
the standard model fields like constant background fields causing
deviations of Lorentz symmetry [1]. This is a very active line of in-
vestigation
with many theoretical results awaiting for experimental
confirmation (for a review see [2]). Usually such proposals have as
a consequence that the dispersion relation for light is modified.
Amore conservative alternative would keep the essential features
of special relativity, like the constancy of the velocity of light, but
leave aside rotation symmetry for instance. This can be achieved
by taking subgroups of the Lorentz group which preserve the con-
stancy
of the velocity of light. Such subgroups were identified and
used to built what is called very special relativity (VSR) [3]. One of
its main features is that the inclusion of P , T or CP symmetries
enlarges VSR to the full Lorentz group so that VSR is only rele-
vant
in theories where one of the discrete symmetries is broken.
Two subgroups of the Lorentz group, SIM(2) and HOM(2), have the
E-mail addresses: jalfaro@puc.cl (J. Alfaro), rivelles@fma.if.usp.br (V.O. Rivelles).
property of rescaling a fixed null vector n
μ
. Then terms contain-
ing
ratios of contractions of n
μ
with other kinematic vectors will
be invariant under transformations of these subgroups. A proposal
to generate mass for neutrinos along these lines was presented in
[4] where an equation for a left-handed fermion incorporating VSR
was given
/p −
1
2
m
2
/n
n
μ
p
μ
ψ
L
=0, (1)
where m sets the VSR scale. When the equation of motion is
squared we find that it describes a free fermion of mass m. The
price to be paid is the presence of non-local operators as well as
the lack of rotational symmetry. In this way it is possible to save
some of the important effects of special relativity and consider
possible violations of space isotropy. Several aspects of VSR have
been considered, like the inclusion of supersymmetry [5,6], curved
spaces [7,8], noncommutativity [9,10], dark matter [11] and also in
cosmology [12].
We
can take this specific realization of VSR and consider the
addition of interaction terms in the context of the usual Lorentz
violating theories. We can regard the inclusion of operators con-
taining
a constant and null vector n
μ
as determining a preferred
direction in space. It breaks Lorentz symmetry to ISO(2) but allow-
ing
a scale transformation on n
μ
the symmetry can be enlarged
to SIM(2). So the inclusion of terms containing ratios of n
μ
con-
tracted
with other kinematic vectors will lead to the consideration
of VSR like terms as that in (1). When a Lorentz invariant action is
extended by the addition of Lorentz violating operators the coeffi-
cients
of such operators are in general arbitrary and unrelated to
http://dx.doi.org/10.1016/j.physletb.2014.05.068
0370-2693/
© 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/). Funded by
SCOAP
3
.