239 research outputs found
Massive Hermitian Gravity
Einstein-Strauss Hermitian gravity was recently formulated as a gauge theory
where the tangent group is taken to be the pseudo-unitary group instead of the
orthogonal group. A Higgs mechanism for massive gravity was also formulated. We
generalize this construction to obtain massive Hermitian gravity with the use
of a complex Higgs multiplet. We show that both the graviton and antisymmetric
tensor acquire the same mass. At the linearized level, the theory is ghost free
around Minkowski background and describes a massive graviton with five degrees
of freedom and an antisymmetric field with three degrees of of freedom. We
determine the strong coupling scales for these degrees of freedom and argue
that the potential nonlinear ghosts, if they exist, have to decouple from the
gravitational degrees of freedom in strong coupling regime.Comment: 10 page
Massive Gravity on Curved Background
We investigate generally covariant theories which admit a Fierz-Pauli mass
term for metric perturbations around an arbitrary curved background. For this
we restore the general covariance of the Fierz-Pauli mass term by introducing
four scalar fields which preserve a certain internal symmetry in their
configuration space. It is then apparent that for each given spacetime metric
this construction corresponds to a completely different generally covariant
massive gravity theory with different symmetries. The proposed approach is
verified by explicit analysis of the physical degrees of freedom of massive
graviton on de Sitter space.Comment: Version accepted for publication; 17 page
Exact Solution to the "Auxiliary Extra Dimension" Model of Massive Gravity
The "Auxiliary Extra Dimension" model was proposed in order to provide a
geometrical interpretation to modifications of general relativity, in
particular to non-linear massive gravity. In this context, the theory was shown
to be ghost free to third order in perturbations, in the decoupling limit. In
this work, we exactly solve the equation of motion in the extra dimension, to
obtain a purely 4-dimensional theory. Using this solution, it is shown that the
ghost appears at the fourth order and beyond. We explore potential
modifications to address the ghost issue and find that their consistent
implementation requires going beyond the present framework.Comment: v3:8 pages, LaTex, a comment and a reference added, version to appear
in PL
Bacteriological conversion in twenty urinary tuberculosis patients treated with ofloxacin, rifampin and isoniazid: a 10-year follow-up study
Twenty patients withuri nary tuberculosis were treated withofloxac in (200 mg/day, 6 months), rifampin (600 mg/day, 3 months) and isoniazid (300 mg/day, 3 months) between 1989 and 1990. All patients were new cases, diagnosed by observation and/or isolation of Mycobacterium tuberculosis in one of the three morning urine samples. Bacteriological culture conversion (negativization) was assessed as a clinical guide of efficacy, comparing it, as the only parameter, against a control group (150 patients) withurina ry tuberculosis who received conventional therapy. Bacteriological follow-up studies were performed in bothgroups monthly for 6 months, then again 6 months later and then every year for 10 years after completion of treatment. In the 20 patients, the initial culture was positive with over 100 colonies per culture (>50%); the smear was positive in 45% of the patients (most were 2+). All strains were susceptible to rifampin, isoniazid and ofloxacin. Two patients discontinued treatment. Beginning withth e first monthof treatment, the bacteriological conversion was 100%, 89.5% and 100% in the remaining controls. In the control group, which received conventional treatment, the conversion was: 90%, 87%, 93% and 100% in the remaining controls. Treatment withofloxacin resulted in a bacteriological conversion similar to that following conventional treatment (p>0.05, Fisher’s exact test). After 10 years of patient follow-up, we conclude that ofloxacin, in combination withrifampin and isoniazid (bothfor 3 months only is effective against M. tuberculosis, providing satisfactory bacteriological and clinical efficacy
Note About Hamiltonian Structure of Non-Linear Massive Gravity
We perform the Hamiltonian analysis of non-linear massive gravity action
studied recently in arXiv:1106.3344 [hep-th]. We show that the Hamiltonian
constraint is the second class constraint. As a result the theory possesses an
odd number of the second class constraints and hence all non physical degrees
of freedom cannot be eliminated.Comment: 15 page
On Non-Linear Actions for Massive Gravity
In this work we present a systematic construction of the potentially
ghost-free non-linear massive gravity actions. The most general action can be
regarded as a 2-parameter deformation of a minimal massive action. Further
extensions vanish in 4 dimensions. The general mass term is constructed in
terms of a "deformed" determinant from which this property can clearly be seen.
In addition, our formulation identifies non-dynamical terms that appear in
previous constructions and which do not contribute to the equations of motion.
We elaborate on the formal structure of these theories as well as some of their
implications.Comment: v3: 22 pages, minor comments added, version to appear in JHE
The Self-Accelerating Universe with Vectors in Massive Gravity
We explore the possibility of realising self-accelerated expansion of the
Universe taking into account the vector components of a massive graviton. The
effective action in the decoupling limit contains an infinite number of terms,
once the vector degrees of freedom are included. These can be re-summed in
physically interesting situations, which result in non-polynomial couplings
between the scalar and vector modes. We show there are self-accelerating
background solutions for this effective action, with the possibility of having
a non-trivial profile for the vector fields. We then study fluctuations around
these solutions and show that there is always a ghost, if a background vector
field is present. When the background vector field is switched off, the ghost
can be avoided, at the price of entering into a strong coupling regime, in
which the vector fluctuations have vanishing kinetic terms. Finally we show
that the inclusion of a bare cosmological constant does not change the previous
conclusions and it does not lead to a ghost mode in the absence of a background
vector field.Comment: 23 pages, 2 figure
Relaxing the cosmological constant: a proof of concept
We propose a technically natural scenario whereby an initially large cosmological constant (c.c.) is relaxed down to the observed value due to the dynamics of a scalar evolving on a very shallow potential. The model crucially relies on a sector that violates the null energy condition (NEC) and gets activated only when the Hubble rate becomes sufficiently small — of the order of the present one. As a result of NEC violation, this low-energy universe evolves into inflation, followed by reheating and the standard Big Bang cosmology. The symmetries of the theory force the c.c. to be the same before and after the NEC-violating phase, so that a late-time observer sees an effective c.c. of the correct magnitude. Importantly, our model allows neither for eternal inflation nor for a set of possible values of dark energy, the latter fixed by the parameters of the theory
EFT of interacting spin-2 fields
We consider the effective field theory of multiple interacting massive spin-2 fields. We focus on the case where the interactions are chosen so that the cutoff is the highest possible, and highlight two distinct classes of theories. In the first class, the mass eigenstates only interact through potential operators that carry no derivatives in unitary gauge at leading order. In the second class, a specific kinetic mixing between the mass eigenstates is included non-linearly. Performing a decoupling and ADM analysis, we point out the existence of a ghost present at a low scale for the first class of interactions. For the second class of interactions where kinetic mixing is included, we derive the full Λ3-decoupling limit and confirm the absence of any ghosts. Nevertheless both formulations can be used to consistently describe an EFT of interacting massive spin-2 fields which, for a suitable technically natural tuning of the EFT, have the same strong coupling scale Λ3. We identify the generic form of EFT corrections in each case. By using Galileon Duality transformations for the specific case of two massive spin-2 fields with suitable couplings, the decoupling limit theory is shown to be a bi-Galileon
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