964 research outputs found

### On Unitarity of Massive Gravity in Three Dimensions

We examine a unitarity of a particular higher-derivative extension of general
relativity in three space-time dimensions, which has been recently shown to be
equivalent to the Pauli-Fierz massive gravity at the linearized approximation
level, and explore a possibility of generalizing the model to higher space-time
dimensions. We find that the model in three dimensions is indeed unitary in the
tree-level, but the corresponding model in higher dimensions is not so due to
the appearance of non-unitary massless spin-2 modes.Comment: 10 pages, references adde

### Aspects of a supersymmetric Brans-Dicke theory

We consider a locally supersymmetric theory where the Planck mass is replaced
by a dynamical superfield. This model can be thought of as the Minimal
Supersymmetric extension of the Brans-Dicke theory (MSBD). The motivation that
underlies this analysis is the research of possible connections between Dark
Energy models based on Brans-Dicke-like theories and supersymmetric Dark Matter
scenarios. We find that the phenomenology associated with the MSBD model is
very different compared to the one of the original Brans-Dicke theory: the
gravitational sector does not couple to the matter sector in a universal metric
way. This feature could make the minimal supersymmetric extension of the BD
idea phenomenologically inconsistent.Comment: 6 pages, one section is adde

### Helicity-1/2 Mode as a Probe of Interactions of Massive Rarita-Schwinger Field

We consider the electromagnetic and gravitational interactions of a massive
Rarita-Schwinger field. Stueckelberg analysis of the system, when coupled to
electromagnetism in flat space or to gravity, reveals in either case that the
effective field theory has a model-independent upper bound on its UV cutoff,
which is finite but parametrically larger than the particle's mass. It is the
helicity-1/2 mode that becomes strongly coupled at the cutoff scale. If the
interactions are inconsistent, the same mode becomes a telltale sign of
pathologies. Alternatively, consistent interactions are those that propagate
this mode within the light cone. Studying its dynamics not only sheds light on
the Velo-Zwanziger acausality, but also elucidates why supergravity and other
known consistent models are pathology-free.Comment: 18 pages, cutoff analysis improved, to appear in PR

### The mass of the graviton and the cosmological constant

We show that the graviton acquires a mass in a de Sitter background given by
$m_{g}^{2}=-{2/3}\Lambda.$ This is precisely the fine-tuning value required for
the perturbed gravitational field to mantain its two degrees of freedom.Comment: Title changed and few details added, without any changes in the
conclusio

### Causal Propagation of a Charged Spin 3/2 Field in an External Electromagnetic Background

We present a Lagrangian for a massive, charged spin 3/2 field in a constant
external electromagnetic background, which correctly propagates only physical
degrees of freedom inside the light cone. The Velo-Zwanziger acausality and
other pathologies such as loss of hyperbolicity or the appearance of unphysical
degrees of freedom are avoided by a judicious choice of non-minimal couplings.
No additional fields or equations besides the spin 3/2 ones are needed to solve
the problem.Comment: 10 pages, references added. To appear in PR

### An Exotic Theory of Massless Spin-Two Fields in Three Dimensions

It is a general belief that the only possible way to consistently deform the
Pauli-Fierz action, changing also the gauge algebra, is general relativity.
Here we show that a different type of deformation exists in three dimensions if
one allows for PT non-invariant terms. The new gauge algebra is different from
that of diffeomorphisms. Furthermore, this deformation can be generalized to
the case of a collection of massless spin-two fields. In this case it describes
a consistent interaction among them.Comment: 21+1 pages. Minor corrections and reference adde

### Rotor Spectra, Berry Phases, and Monopole Fields: from Antiferromagnets to QCD

The order parameter of a finite system with a spontaneously broken continuous
global symmetry acts as a quantum mechanical rotor. Both antiferromagnets with
a spontaneously broken $SU(2)_s$ spin symmetry and massless QCD with a broken
$SU(2)_L \times SU(2)_R$ chiral symmetry have rotor spectra when considered in
a finite volume. When an electron or hole is doped into an antiferromagnet or
when a nucleon is propagating through the QCD vacuum, a Berry phase arises from
a monopole field and the angular momentum of the rotor is quantized in
half-integer units.Comment: 4 page

### An equivalence principle for scalar forces

The equivalence of inertial and gravitational masses is a defining feature of
general relativity. Here, we clarify the status of the equivalence principle
for interactions mediated by a universally coupled scalar, motivated partly by
recent attempts to modify gravity at cosmological distances. Although a
universal scalar-matter coupling is not mandatory, once postulated, it is
stable against classical and quantum renormalizations in the matter sector. The
coupling strength itself is subject to renormalization of course. The scalar
equivalence principle is violated only for objects for which either the
graviton self-interaction or the scalar self-interaction is important---the
first applies to black holes, while the second type of violation is avoided if
the scalar is Galilean-symmetric.Comment: 4 pages, 1 figur

### Topological Aspect of high-$T_c$ Superconductivity, Fractional Quantum Hall Effect and Berry Phase

We have analysed here the equivalence of RVB states with $\nu=1/2$ FQH states
in terms of the Berry Phase which is associated with the chiral anomaly in 3+1
dimensions. It is observed that the 3-dimensional spinons and holons are
characterised by the non-Abelian Berry phase and these reduce to 1/2 fractional
statistics when the motion is confined to the equatorial planes. The
topological mechanism of superconductivity is analogous to the topological
aspects of fractional quantum Hall effect with $\nu=1/2$.Comment: 12 pages latex fil

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