6 research outputs found
The effective Equation of State in Palatini cosmology
We investigate how the cosmological Equation of State can be used for
scrutinizing extended theories of gravity, in particular, the Palatini
gravity. Specifically, the approach consists, at first, in investigating the
effective Equation of State produced by a given model. Then, the inverse
problem can also be considered in view of determining which models are
compatible with a given effective Equation of State. We consider and solve some
cases and show that, for example, power-law models are (the only models)
capable of transforming barotropic Equations of State into effective barotropic
ones. Moreover, the form of Equation of State is preserved (only) for ,
as expected. In this perspective, modified Equations of State are a feature
capable of distinguishing Extended Gravity with respect to General Relativity.
We also investigate quadratic and non-homogeneous effective Equations of State
showing, in particular, that they contain the Starobinsky model and other ones.Comment: 19 page
Relativistic GPS in 3-dimensions
We extend to three dimensions the proposal of a completely relativistic
positioning system (rPS). The system does not rely on approximations, in fact,
it works at a few Schwarzschild radii from a black hole, and it does not rely
on Newtonian physics or special relativity. Since general relativity (GR)
claims to be our fundamental framework to describe classical physics, it must
provide tools to bootstrap physics within the theory itself, without relying on
previous approximated frameworks. The rPS is able to self-diagnose, that is, it
detects deviations from assumptions about the gravitational field and
consequently stops operations; in addition it is robust, i.e., it is able to
autonomously restore operations when assumptions are restored. From a more
general viewpoint, the rPS is equivalent to geodesy in spacetime, which
establishes a (conventional) coordinate system on a surface by means of
measurements within the surface itself, as well as allowing it to extract
information about the intrinsic geometry of the same surface. In other words,
the positioning system is potentially able to extract information about the
gravitational field (which in fact is identified with the geometry of
spacetime) in addition to the gravitational theory, which describes its
dynamics. Thus, it becomes a framework within which one can operationally
distinguish different theories of gravitation.Comment: 29 pages, 8 figure
Introduction to Loop Quantum Gravity. The Holst's action and the covariant formalism
We review Holst formalism and we discuss dynamical equivalence with standard
GR (in dimension 4). Holst formalism is written for a spin coframe field
and a -connection on spacetime and
it depends on the Holst parameter .
We show the model is dynamically equivalent to standard GR, in the sense that
up to a pointwise -gauge transformation acting on frame indices,
solutions of the two models are in one-to-one correspondence. Hence the two
models are classically equivalent.
One can also introduce new variables by splitting the spin connection into a
pair of a -connection and a -valued 1-form
. The construction of these new variables relies on a particular
algebraic structure, called a reductive splitting. A reductive splitting is a
weaker structure than requiring that the gauge group splits as the products of
two sub-groups, as it happens in Euclidean signature in the selfdual
formulation originally introduced in this context by Ashtekar, and it still
allows to deal with the Lorentzian signature without resorting to
complexifications.
The reductive splitting of is not unique and it is
parameterized by a real parameter , called the Immirzi parameter. The
splitting is here done on spacetime, not on space, to obtain a
-connection , which is called the Barbero-Immirzi connection
on spacetime. One obtains a covariant model depending on the fields which is again dynamically equivalent to standard GR (as
well as the Holst action).
Usually, in the literature one sets for the sake of
simplicity. Here we keep the Holst and Immirzi parameters distinct to show that
eventually, only will survive in boundary field equations.Comment: 19 page
Myositis/myasthenia after pembrolizumab in a bladder cancer patient with an autoimmunity-associated HLA: Immune\u2013biological evaluation and case report
Pembrolizumab (mAb to PD-1) has been recently approved for the therapy of pretreated urothelial cancer. Despite the efficacy, it is often accompanied by unpredictable and sometime severe immune-related (ir) adverse events (AEs). Here, we report the clinical and immune\u2013biological characterization of a patient with a metastatic bladder cancer who developed myositis signs (M) and a myasthenia-like syndrome (MLS) during treatment with pembrolizumab. The patient presented an autoimmunity-associated HLA haplotype (HLA-A*02/HLA-B*08/HLA-C*07/HLA-DRB1*03) and experienced an increase in activated CD8 T-cells along the treatment. The symptomatology regressed after pembrolizumab discontinuation and a pyridostigmine and steroids-based therapy. This is the first report of concurrent M and MLS appearance in cancer patients receiving pembrolizumab. More efforts are needed to define early the risk and the clinical meaning of irAEs in this setting
The generally covariant meaning of space distances
We propose a covariant and geometric framework to introduce space distances as they are used by astronomers. In particular, we extend the definition of space distances from the one used between events to non-test bodies with horizons and singularities so that the definition extends through the horizons and it matches the protocol used to measure them. The definition we propose can be used in standard general relativity although it extends directly to Weyl geometries to encompass a number of modified theories, extended theories in particular