27 research outputs found
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
Inconsistencies of Massive Charged Gravitating Higher Spins
We examine the causality and degrees of freedom (DoF) problems encountered by
charged, gravitating, massive higher spin fields. For spin s=3/2, making the
metric dynamical yields improved causality bounds. These involve only the mass,
the product eM_P of the charge and Planck mass and the cosmological constant
\Lambda. The bounds are themselves related to a gauge invariance of the
timelike component of the field equation at the onset of acausality. While
propagation is causal in arbitrary E/M backgrounds, the allowed mass ranges of
parameters are of Planck order. Generically, interacting spins s>3/2 are
subject to DoF violations as well as to acausality; the former must be overcome
before analysis of the latter can even begin. Here we review both difficulties
for charged s=2 and show that while a g-factor of 1/2 solves the DoF problem,
acausality persists for any g. Separately we establish that no s=2 theory --DoF
preserving or otherwise -- can be tree unitary.Comment: 25 pages, late
Partial Masslessness of Higher Spins in (A)dS
Massive spin s>=3/2 fields can become partially massless in cosmological
backgrounds. In the plane spanned by m^2 and \Lambda, there are lines where new
gauge invariances permit intermediate sets of higher helicities, rather than
the usual flat space extremes of all 2s+1 massive or just 2 massless
helicities. These gauge lines divide the (m^2,\Lambda) plane into unitarily
allowed or forbidden intermediate regions where all 2s+1 massive helicities
propagate but lower helicity states can have negative norms. We derive these
consequences for s=3/2,2 by studying both their canonical (anti)commutators and
the transmutation of massive constraints to partially massless Bianchi
identities. For s=2, a Hamiltonian analysis exhibits the absence of zero
helicity modes in the partially massless sector. For s=5/2,3 we derive Bianchi
identities and their accompanying gauge invariances for the various partially
massless theories with propagating helicities (+/-5/2,+/-3/2) and (+/-3,+/-2),
(+/-3,+/-2,+/-1), respectively. Of these, only the s=3 models are unitary. To
these ends, we also provide the half integer generalization of the integer spin
wave operators of Lichnerowicz. Partial masslessness applies to all higher
spins in (A)dS as seen by their degree of freedom counts. Finally a derivation
of massive d=4 constraints by dimensional reduction from their d=5 massless
Bianchi identity ancestors is given.Comment: 35 pages, LaTeX, uses slashed.sty, version to appear in Nucl. Phys.
Massive Spin 3/2 Electrodynamics
We study the general non-minimally coupled charged massive spin 3/2 model
both for its low energy phenomenological properties and for its unitarity,
causality and degrees of freedom behaviour. When the model is viewed as an
effective theory, its parameters (after ensuring the correct excitation count)
are related to physical characteristics, such as the magnetic moment g factor,
by means of low energy theorems. We also provide the corresponding higher spin
generalisation. Separately, we consider both low and high energy unitarity, as
well as the causality aspects of our models. None (including truncated N=2
supergravity) is free of the minimal model's acausality.Comment: 23 pages, 1 figure, LaTeX and axodraw.sty, novel Majorana-type term
included; results unaltere
Improved Xenobiotic Metabolism and Reduced Susceptibility to Cancer in Gluten-Sensitive Macaques upon Introduction of a Gluten-Free Diet
A non-human primate (NHP) model of gluten sensitivity was employed to study the gene perturbations associated with dietary gluten changes in small intestinal tissues from gluten-sensitive rhesus macaques (Macaca mulatta).Stages of remission and relapse were accomplished in gluten-sensitive animals by administration of gluten-free (GFD) and gluten-containing (GD) diets, as described previously. Pin-head-sized biopsies, obtained non-invasively by pediatric endoscope from duodenum while on GFD or GD, were used for preparation of total RNA and gene profiling, using the commercial Rhesus Macaque Microarray (Agilent Technologies),targeting expression of over 20,000 genes.When compared with normal healthy control, gluten-sensitive macaques showed differential gene expressions induced by GD. While observed gene perturbations were classified into one of 12 overlapping categories--cancer, metabolism, digestive tract function, immune response, cell growth, signal transduction, autoimmunity, detoxification of xenobiotics, apoptosis, actin-collagen deposition, neuronal and unknown function--this study focused on cancer-related gene networks such as cytochrome P450 family (detoxification function) and actin-collagen-matrix metalloproteinases (MMP) genes.A loss of detoxification function paralleled with necessity to metabolize carcinogens was revealed in gluten-sensitive animals while on GD. An increase in cancer-promoting factors and a simultaneous decrease in cancer-preventing factors associated with altered expression of actin-collagen-MMP gene network were noted. In addition, gluten-sensitive macaques showed reduced number of differentially expressed genes including the cancer-associated ones upon withdrawal of dietary gluten. Taken together, these findings indicate potentially expanded utility of gluten-sensitive rhesus macaques in cancer research