7 research outputs found
QCD Universality recovered via the Total Available Quadri-Scalar: Atot
After presenting a brief review of the phenomenology of the Leading Effect,
we define a new variable, the ``Total Available Quadri-Scalar'' (Atot), and
propose it as the invariant quantity effectively available for the production
of the multihadronic final states. The introduction and the definition of this
new variable are justified by means of simple geometrical-kinematical
considerations and we show that Atot reduces to the so-called Effective Energy
in the single specific situation where the use of the latter applies. Using
Atot to re-plot existing data, the quantity is shown to be a
``Universality Feature'' - that is, independent from the process under exam,
the collider nominal energy, and even from the hadronic invariant mass - as
imposed by QCD Universality.Comment: V1: 24 pages, 4 figures; V2: reduced to 18 pages, layout and
presentation improved, content unchanged; V3: definitive published version,
adp latex style, a comparison to GPDs added, content unchange
A radiation-like era before inflation
We show that the semiclassical approximation to the Wheeler-DeWitt equation
for the minisuperspace of a minimally coupled scalar field in the spatially
flat de Sitter Universe prompts the existence of an initial power-law evolution
driven by non-adiabatic terms from the gravitational wavefunction which act
like radiation. This simple model hence describes the onset of inflation from a
previous radiation-like expansion during which the cosmological constant is
already present but subleading.Comment: LaTeX, 8 pages, no figures; final version to be published in JCA
A note on second-order perturbations of non-canonical scalar fields
We study second-order perturbations for a general non-canonical scalar field,
minimally coupled to gravity, on the unperturbed FRW background, where metric
fluctuations are neglected a priori. By employing different approaches to
cosmological perturbation theory, we show that, even in this simplified set-up,
the second-order perturbations to the stress tensor, the energy density and the
pressure display potential instabilities, which are not present at linear
order. The conditions on the Lagrangian under which these instabilities take
place are provided. We also discuss briefly the significance of our analysis in
light of the possible linearization instability of these fields about the FRW
background.Comment: 8 page, Revtex 4. Clarifications added, results unchanged; [v3] 10
pages, matches with the published version, Discussion for specific cases
expanded and preliminary results including the metric perturbations discusse
Hints of (trans-Planckian) asymptotic freedom in semiclassical cosmology
We employ the semiclassical approximation to the Wheeler-DeWitt equation in
the spatially flat de Sitter Universe to investigate the dynamics of a
minimally coupled scalar field near the Planck scale. We find that, contrary to
naive intuition, the effects of quantum gravitational fluctuations become
negligible and the scalar field states asymptotically approach plane-waves at
very early times. These states can then be used as initial conditions for the
quantum states of matter to show that each mode essentially originated in the
minimum energy vacuum. Although the full quantum dynamics cannot be solved
exactly for the case at hand, our results can be considered as supporting the
general idea of asymptotic safety in quantum gravity.Comment: 11 pages, 2 figures; replaced to match content of published versio
The Cosmological Constant and Horava-Lifshitz Gravity
Horava-Lifshitz theory of gravity with detailed balance is plagued by the
presence of a negative bare (or geometrical) cosmological constant which makes
its cosmology clash with observations. We argue that adding the effects of the
large vacuum energy of quantum matter fields, this bare cosmological constant
can be approximately compensated to account for the small observed (total)
cosmological constant. Even though we cannot address the fine-tuning problem in
this way, we are able to establish a relation between the smallness of observed
cosmological constant and the length scale at which dimension 4 corrections to
the Einstein gravity become significant for cosmology. This scale turns out to
be approximately 5 times the Planck length for an (almost) vanishing observed
cosmological constant and we therefore argue that its smallness guarantees that
Lorentz invariance is broken only at very small scales. We are also able to
provide a first rough estimation for the infrared values of the parameters of
the theory and .Comment: 9 pages, Late
Selection of the optimal candidate to mitraclip for secondary mitral regurgitation : Beyond mitral valve morphology
Secondary mitral regurgitation (MR) occurs despite structurally normal valve apparatus due to an underlying disease of the myocardium leading to disruption of the balance between tethering and closing forces with ensuing failure of leaflet coaptation. In patients with heart failure (HF) and left ventricular dysfunction, secondary MR is independently associated with poor outcome, yet prognostic benefits related to the correction of MR have remained elusive. Surgery is not recommended for the correction of secondary MR outside coronary artery bypass grafting. Percutaneous mitral valve repair (PMVR) with MitraClip implantation has recently evolved as a new transcatheter treatment option of inoperable or high-risk patients with severe MR, with promising results supporting the extension of guideline recommendations. MitraClip is highly effective in reducing secondary MR in HF patients. However, the derived clinical benefit is still controversial as two randomized trials directly comparing PMVR vs. optimal medical therapy in severe secondary MR yielded virtually opposite conclusions. We reviewed current evidence to identify predictors of PMVR-related outcomes in secondary MR useful to improve the timing and the selection of patients who would derive maximal benefit from MitraClip intervention. Beyond mitral valve anatomy, optimal candidate selection should rely on a comprehensive diagnostic workup and a fine-tuned risk stratification process aimed at (i) recognizing the substantial heterogeneity of secondary MR and its complex interaction with the myocardium, (ii) foreseeing hemodynamic consequences of PMVR, (iii) anticipating futility and (iv) improving symptoms, quality of life and overall survival