Flavio Mercati

CSF markers in Alzheimer disease patients are not related to the different degree of cognitive impairment

Standard markers in cerebrospinal fluid (CSF), as soluble amyloid beta 1-42 (Abeta1-42) and total tau protein (t-tau), may contribute to dementia subtypes diagnostic accuracy. Yet, their sensitivity to assess the different degree of cognitive deficit is not fully clarified. Our study analyses Abeta1-42 and t-tau CSF levels in different cohorts of Alzheimers disease (AD) patients, distinguished as early AD (mild cognitively impaired subjects recently converted to AD), mild AD (MMSE<23; > or =18), and moderately advanced AD (MMSE<18). The control group was represented by age-matched patients affected by depressive pseudo-dementia. Reduced Abeta1-42 and increased t-tau CSF levels were confirmed as hallmarks of AD at any disease stage. In early AD patients, Abeta1-42 levels were already significantly low, if compared to the control group (336 vs 867 ng/L; p<0.0001). On the contrary, Abeta1-42 levels did not differ between AD subgroups, and in particular between mild to moderate AD. A significant progressive increase of t-tau concentration was found when comparing early AD (269 ng/L) to more advanced AD stages (468 ng/L and 495 ng/L for mild and moderate AD, respectively). Our findings confirm that the impairment of amyloidogenic cascade is an early, even pre-clinical process, but suggest that soluble Abeta1-42 concentration has a negligible correlation with the clinical progression. Conversely, t-tau concentration correlates with the transition towards marked cognitive impairment.

Constraining the Energy-Momentum Dispersion Relation with Planck-Scale Sensitivity Using Cold Atoms

We use the results of ultraprecise cold-atom-recoil experiments to constrain the form of the energy-momentum dispersion relation, a structure that is expected to be modified in several quantum-gravity approaches. Our strategy of analysis applies to the nonrelativistic (small speeds) limit of the dispersion relation, and is therefore complementary to an analogous ongoing effort of investigation of the dispersion relation in the ultrarelativistic regime using observations in astrophysics. For the leading correction in the nonrelativistic limit the exceptional sensitivity of cold-atom-recoil experiments remarkably allows us to set a limit within a single order of magnitude of the desired Planck-scale level, thereby providing the first example of Planck-scale sensitivity in the study of the dispersion relation in controlled laboratory experiments.

Relative locality in κ-Poincaré

We show that the ?-Poincar? Hopf algebra can be interpreted in the framework of curved momentum space leading to relative locality. We study the geometric properties of the momentum space described by ?-Poincar? and derive the consequences for particle propagation and energy?momentum conservation laws in interaction vertices, obtaining for the first time a coherent and fully workable model of the deformed relativistic kinematics implied by ?-Poincar?. We describe the action of boost transformations on multi-particle systems, showing that the covariance of the composed momenta requires a dependence of the rapidity parameter on the particle momenta themselves. Finally, we show that this particular form of the boost transformations keeps the validity of the relativity principle, demonstrating the invariance of the equations of motion under boost transformations.

A no-pure-boost uncertainty principle from spacetime noncommutativity

Abstract We study boost and space-rotation transformations in κ-Minkowski noncommutative spacetime, using the techniques that some of us had previously developed [A. Agostini, G. Amelino-Camelia, M. Arzano, A. Marciano, R.A. Tacchi, hep-th/0607221 ] for a description of translations in κ-Minkowski, which in particular led to the introduction of translation transformation parameters that do not commute with the spacetime coordinates. We find a similar description of boosts and space rotations, which allows us to identify some associated conserved charges, but the form of the commutators between transformation parameters and spacetime coordinates is incompatible with the possibility of a pure boost.

Noether analysis of the twisted Hopf symmetries of canonical noncommutative spacetimes

We study the twisted-Hopf-algebra symmetries of observer-independent canonical spacetime noncommutativity, for which the commutators of the spacetime coordinates take the form [x̂, x̂ ] = iθ with observer-independent (and coordinate-independent) θ . We find that it is necessary to introduce nontrivial commutators between transformation parameters and spacetime coordinates, and that the form of these commutators implies that all symmetry transformations must include a translation component. We show that with our noncommutative transformation parameters the Noether analysis of the symmetries is straightforward, and we compare our canonical-noncommutativity results with the structure of the conserved charges and the “no-pure-boost” requirement derived in a previous study of κ-Minkowski noncommutativity. We also verify that, while at intermediate stages of the analysis we do find terms that depend on the ordering convention adopted in setting up the Weyl map, the final result for the conserved charges is reassuringly independent of the choice of Weyl map and (the corresponding choice of) star product. ∗Supported by EU Marie Curie fellowship EIF-025947-QGNC

Probing the quantum-gravity realm with slow atoms

For the study of Planck-scale modifications of the energy–momentum dispersion relation, which had been previously focused on the implications for ultrarelativistic particles, we consider the possible role of experiments involving nonrelativistic particles, and particularly atoms. We extend a recent result establishing that measurements of atom-recoil frequency can provide an insight that is valuable for some theoretical models. From a broader perspective we analyze the complementarity of the nonrelativistic and the ultrarelativistic regimes in this research area.

Discreteness of area in noncommutative space

Abstract We introduce an area operator for the Moyal noncommutative plane. We find that the spectrum is discrete, but, contrary to the expectation formulated by other authors, not characterized by a “minimum-area principle”. We show that an intuitive analysis of the uncertainty relations obtained from Moyal-plane noncommutativity is fully consistent with our results for the spectrum, and we argue that our area operator should be generalizable to several other noncommutative spaces. We also observe that the properties of distances and areas in the Moyal plane expose some weaknesses in the line of reasoning adopted in some of the heuristic analyses of the measurability of geometric spacetime observables in the quantum-gravity realm.

Locality and the relativity principle beyond special relativity

Locality of interactions is an essential ingredient of Special Relativity. Recently, a new framework under the name of relative locality [G. Amelino-Camelia, L. Freidel, J. Kowalski-Glikman, and L. Smolin, arXiv:1101.0931.] has been proposed as a way to consider Planckian modifications of the relativistic dynamics of particles. We note in this paper that the loss of absolute locality is a general feature of theories beyond Special Relativity with an implementation of a relativity principle. We give an explicit construction of such an implementation and compare it both with the previously mentioned framework of relative locality and the so-called Doubly Special Relativity theories.

Relativistic kinematics beyond Special Relativity

In the context of departures from Special Relativity written as a momentum power expansion in the inverse of an ultraviolet energy scale M, we derive the constraints that the relativity principle imposes between coefficients of a deformed composition law, dispersion relation, and transformation laws, at first order in the power expansion. In particular, we find that, at that order, the consistency of a modification of the energy-momentum composition law fixes the modification in the dispersion relation. We therefore obtain the most generic modification of Special Relativity that preserves the relativity principle at leading order in 1/M.

GRAVITY IN QUANTUM SPACE–TIME

The literature on quantum-gravity-inspired scenarios for the quantization of space–time has so far focused on particle-physics-like studies. This is partly justified by the present limitations of our understanding of quantum gravity theories, but we here argue that valuable insight can be gained through semi-heuristic analyses of the implications for gravitational phenomena of some results obtained in the quantum space–time literature. In particular, we show that the types of description of particle propagation that emerged in certain quantum space–time frameworks have striking implications for gravitational collapse and for the behavior of gravity at large distances.