Modifications to Lorentz invariant dispersion in relatively boosted frames

We investigate the implications of energy-dependence of the speed of photons, one of the candidate effects of quantum-gravity theories that has been most studied recently, from the perspective of observations in different reference frames. We examine how a simultaneous burst of photons would be measured by two observers with a relative velocity, establishing some associated conditions for the consistency of theories. For scenarios where the Lorentz transformations remain valid these consistency conditions allow us to characterize the violations of Lorentz symmetry through an explicit description of the modification of the quantum-gravity scale in boosted frames with respect to its definition in a preferred frame. When applied to relativistic scenarios with a deformation of Lorentz invariance that preserves the equivalence of inertial observers, we find an insightful characterization of the necessity to adopt in such frameworks non-classical features of spacetime geometry, e.g. events that are at the same spacetime point for one observer cannot be considered at the same spacetime point for other observers. Our findings also suggest that, at least in principle (and perhaps one day even in practice), measurements of the dispersion of photons in relatively boosted frames can be particularly valuable for the purpose of testing these scenarios.Comment: Accepted for publication in Phys. Rev.

About 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 \cite{AmelinoCamelia:2011bm} 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.Comment: 10 pages, no figure

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 (ultrafast) 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 insight that is valuable for some theoretical models. And from a broader perspective we analyze the complementarity of the nonrelativistic and the ultrarelativistic regimes in this research area.Comment: LaTex, 13 page

Gravity in quantum spacetime

The literature on quantum-gravity-inspired scenarios for the quantization of spacetime 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-spacetime literature. In particular, we show that the types of description of particle propagation that emerged in certain quantum-spacetime frameworks have striking implications for gravitational collapse and for the behaviour of gravity at large distances.Comment: This essay received honorable mention in the Gravity Research Foundation 2010 Awards for Essays on Gravitatio

OPERA-reassessing data on the energy dependence of the speed of neutrinos

We offer a preliminary exploration of the two sides of the challenge provided by the recent OPERA data on superluminal neutrinos. On one side we stress that some aspects of this result are puzzling even from the perspective of the wild quantum-gravity literature, where arguments in favor of the possibility of superluminal propagation have been presented, but not considering the possibility of such a sizeable effect for neutrinos of such low energies. We feel this must encourage particularly severe scrutiny of the OPERA result. On the other side, we notice that the OPERA result is reasonably consistent with $\mu$-neutrino-speed data previously obtained at FERMILAB, reported in papers of 2007 and 1979. And it is intriguing that these FERMILAB79 and FERMILAB07 results, when combined with the new OPERA result, in principle provide a window on $\mu$-neutrino speeds at different energies broad enough to compare alternative phenomenological models. We test the discriminating power of such an approach by using as illustrative examples the case of special-relativistic tachyons, the case of "Coleman-Glashow-type" momentum-independent violations of the special-relativistic speed law, and the cases of linear and quadratic energy dependence of the speed of ultrarelativistic muon neutrinos. Even just using $\mu$-neutrino data in the range from $\sim$ 3 GeVs to $\sim$ 200 GeVs the special-relativistic tachyon and the quadratic-dependence case are clearly disfavoured. The linear-dependence case gives a marginally consistent picture and the Coleman-Glashow scenario fits robustly the data. We also comment on Supernova 1987a and its relevance for consideration of other neutrino species, also in relation with some scenarios that appeared in the large-extra-dimension literature.Comment: some references added; figs.1 and 2 redrawn for better visibility of the effects of bias1979; some sentences which had been written a bit too "densely" in V1 are now more readable in this V

Neuroendocrine responses in neonatal mother-deprived rabbits

To study both short- and long-term adaptation mechanisms activated by rabbits which were separated from their mothers (DLS) for 48 h between postnatal days 9 and 11, we examined plasma corticosterone concentrations before, during, and after DLS as well as the expression of glucocorticoid receptor (GR) in the hippocampus and the adrenal axis responses to a mild stress stimuli or exogenous ACTH injection. At postnatal day 10, plasma corticosterone concentration of DLS rabbits was similar to that of controls, but rose two-fold at day 11 (17.7 ± 1.3 vs. 9.3 ± 1.2 μg/dl, P < 0.01) and then decreased at day 12, when suckling was allowed again, to match those of controls with no difference thereafter. At postnatal day 14, both control and DLS rabbits had similar basal corticosterone concentrations (2.2 ± 0.4 vs. 2.3 ± 1.1 μg/dl, respectively) as well as at day 120 (8.8 ± 3.2 vs. 9.7 ± 2.8 μg/dl, respectively). After the standardized stress stimulus, plasma corticosterone concentrations were lower in DLS rabbits than controls at postnatal days 14 (P < 0.01) and 120 (P < 0.05). At day 120, corticosterone levels rose similarly seven-fold (P < 0.01) within 30 min after ACTH administration and remained sustained thereafter in both control and DLS rabbits. Positive immunoreactivity for GR was detected in the hippocampus and in the dorsal medial hypothalamic region at postnatal day 14. The present data suggest that 48 h DLS from postnatal days 9 to 11 results in a modified hypothalamic–pituitary–adrenal axis reactivity later in life

Transcriptome changes induced by Arbuscular mycorrhizal symbiosis in leaves of durum wheat (Triticum durum Desf.) promote higher salt tolerance

The salinity of soil is a relevant environmental problem around the world, with climate change raising its relevance, particularly in arid and semiarid areas. Arbuscular Mycorrhizal Fungi (AMF) positively affect plant growth and health by mitigating biotic and abiotic stresses, including salt stress. The mechanisms through which these benefits manifest are, however, still unclear. This work aimed to identify key genes involved in the response to salt stress induced by AMF using RNA-Seq analysis on durum wheat (Triticum turgidum L. subsp. durum Desf. Husn.). Five hundred sixty-three differentially expressed genes (DEGs), many of which involved in pathways related to plant stress responses, were identified. The expression of genes involved in trehalose metabolism, RNA processing, vesicle trafficking, cell wall organization, and signal transduction was significantly enhanced by the AMF symbiosis. A downregulation of genes involved in both enzymatic and non-enzymatic oxidative stress responses as well as amino acids, lipids, and carbohydrates metabolisms was also detected, suggesting a lower oxidative stress condition in the AMF inoculated plants. Interestingly, many transcription factor families, including WRKY, NAC, and MYB, already known for their key role in plant abiotic stress response, were found differentially expressed between treatments. This study provides valuable insights on AMF-induced gene expression modulation and the beneficial effects of plant-AMF interaction in durum wheat under salt stress

Relative Locality in κ\kappa-Poincar\'e

We show that the $\kappa$-Poincar\'e Hopf algebra can be interpreted in the framework of curved momentum space leading to the relativity of locality \cite{AFKS}. We study the geometric properties of the momentum space described by $\kappa$-Poincar\'e, and derive the consequences for particles 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 $\kappa$-Poincar\'e. We describe the action of boost transformations on multi-particles systems, showing that in order to keep covariant the composed momenta it is necessary to introduce a dependence of the rapidity parameter on the particles 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.Comment: 24 pages, 4 figures, 1 table. v2 matches accepted CQG versio

Duality and ontology

A ‘duality’ is a formal mapping between the spaces of solutions of two empirically equivalent theories. In recent times, dualities have been found to be pervasive in string theory and quantum field theory. Naïvely interpreted, duality-related theories appear to make very different ontological claims about the world—differing in e.g. space-time structure, fundamental ontology, and mereological structure. In light of this, duality-related theories raise questions familiar from discussions of underdetermination in the philosophy of science: in the presence of dual theories, what is one to say about the ontology of the world? In this paper, we undertake a comprehensive and non-technical survey of the landscape of possible ontological interpretations of duality-related theories. We provide a significantly enriched and clarified taxonomy of options—several of which are novel to the literature

The presence and localization of apelin in the sheep abomasum: impact of diets characterized by different chemical composition

The apelinergic system is a complex system including the apelin peptide (AP), initially isolated in 1998 from bovine stomach homogenates and its receptor, named APJ receptor. The apelin peptide is extensively expressed in several human and laboratory animal organs (heart, lung, brain, mammary gland). Between the different roles hypothesize for apelin there are also the control of blood pressure and the stimulation of drinking behavior in rats. Recently its expression was also evidenced in the basal glandular portion of the stomach in laboratory animals, allowing to hypothesize its intervention in the control of acid secretion. No data concerning its presence and distribution in the abomasums of the sheep are present at the moment. So, we decided to test the presence and distribution of apelin in the abomasums of the sheep and the possible existence of a variability as a consequence of the different water content of the diet.The experiment was conducted using 50 sheep fed on Apennine semi-natural pasture for two experimental periods: in the first period the animals were fed for 45 days on the pasture at the maximum of its flowering; in the second one the animals were fed on the same pasture until its maximum dryness but the half of them daily received adiet integration of cereals. At the end of each experimental period, some animals were regularly slaughtered at the local abattoir, the abomasum specimens were immediately removed and some of them processed for routine tissue-embedding preparation while other for molecular biology. The immunohistochemical reaction was visualized on 5 µm serial sections, using a primary rabbit polyclonal antibody (anti-AP), the avidin-biotin-complex and the DAB as the chromogen. The immunohistochemical study showed a peculiar immunoreaction for AP in the abomasum of the animals examined. In particular, a immunopositive reaction for AP was evident in the cells of the basal third of the tubular glands and they were mainly of the closed type, with an oval or round shape and contained many perinuclear granules. The immunopositive reactions didn’t evidence any difference both in the localization and in the number of the positive cells, between the different groups. Immuno-positivity for AP was not observed in any other histological structure or in the sections utilized as negative controls.These results allow us to conclude that AP is present in the glandular tissue of the abomasums of the sheep, as observed in laboratory animals, with a peculiar cytoplasmatic localization and to hypothesize that AP is involved in the control of gastric secretion, probably via APJ receptor. The AP expression in the stomach doesn’t seem to be influenced by the water content of the diets with a positivity that appears to be localized in the same glandular portion between the different animal groups