arXiv subjects

Luca Maccione

Publications and source records attributed to Luca Maccione.

34 records · Page 2Linked to original sources

arXiv2011

Quantum Gravity phenomenology: achievements and challenges

Motivated by scenarios of quantum gravity, Planck-suppressed deviations from Lorentz invariance are expected at observable energies. Ultra-High-Energy Cosmic Rays, the most energetic particles ever observed in nature, yielded in the last two years strong constraints on deviations suppressed by $O(E^{2}/\Mpl^{2})$ and also, for the first time, on space-time foam, stringy inspired models of quantum gravity. We review the most important achievements and discuss future outlooks.

astro-ph.HE↗

arXiv2011

Lorentz Invariance Violation and Chemical Composition of Ultra High Energy Cosmic Rays

Motivated by experimental indications of a significant presence of heavy nuclei in the cosmic ray flux at ultra high energies ($\gtrsim 10^{19} \eV$), we consider the effects of Planck scale suppressed Lorentz Invariance Violation (LIV) on the propagation of cosmic ray nuclei. In particular we focus on LIV effects on the photodisintegration of nuclei onto the background radiation fields. After a general discussion of the behavior of the relevant quantities, we apply our formalism to a simplified model where the LIV parameters of the various nuclei are assumed to kinematically result from a single LIV parameter for the constituent nucleons, $η$, and we derive constraints on $η$. Assuming a nucleus of a particular species to be actually present at $10^{20}$ eV the following constraints can be placed: $-3\times10^{-2} \lesssim η\lesssim 4$ for $^{56}$Fe, $-2\times10^{-3} \lesssim η\lesssim 3\times10^{-2}$ for $^{16}$O and $-7\times10^{-5} \lesssim η\lesssim 1\times10^{-4}$ for $^{4}$He, respectively.

astro-ph.HE↗

arXiv2011

A consistent interpretation of recent CR nuclei and electron spectra

We try to interpret the recently updated measurement of the cosmic ray electron (CRE) spectrum observed by Fermi-LAT, together with PAMELA data on positron fraction, in a single-component scenario adopting different propagation setups; we find that the model is not adequate to reproduce the two datasets, so the evidence of an extra primary component of electrons and positrons is strengthened. Instead, a double component scenario computed in a Kraichnan-like diffusion setup (which is suggested by B/C and $\bar{p}$ data) gives a satisfactory fit of all exisiting measurements. We confirm that nearby pulsars are good source candidates for the required $e^\pm$ extra-component and we show that the predicted CRE anisotropy in our scenario is compatible with Fermi-LAT recently published constraints.

astro-ph.HE↗

arXiv2010

Implications of the Cosmic Ray Electron Spectrum and Anisotropy measured with Fermi-LAT

The Fermi Large Area Telescope (LAT) collaboration recently released the updated results of the measurement of the cosmic ray electron (CRE) spectrum and published its first constraints on the CRE anisotropy. With respect to the previous Fermi-LAT results, the CRE spectrum measurement was extended down from 20 to 7 GeV, thus providing a better lever arm to discriminate theoretical models. Here we show that the new data strengthen the evidence for the presence of two distinct electron and positron spectral components. Furthermore, we show that under such hypothesis most relevant CRE and positron data sets are remarkably well reproduced. Consistent fits of cosmic-ray nuclei and antiproton data, which are crucial to validate the adopted propagation setup(s) and to fix the solar modulation potential, are obtained for the Kraichnan and plain-diffusion propagation setups, while the Kolmogorov one is disfavored. We then confirm that nearby pulsars are viable source candidates of the required $e^\pm$ extra-component. In that case, we show that the predicted CRE anisotropy is compatible with Fermi-LAT constraints and that a positive detection should be at hand of that observatory. Models assuming that only nearby supernova remnants contribute to the high energy tail of the observed CRE spectrum are in contrast with anisotropy limits.

astro-ph.HE↗

arXiv2010

Unified interpretation of cosmic-ray nuclei and antiproton recent measurements

We use our numerical code, DRAGON, to study the implications of recent data on our knowledge of the propagation properties of cosmic ray nuclei in the Galaxy. We show that B/C (as well as N/O and C/O) data, including those recently taken by CREAM, and ${\bar p}/p$ data, especially including recent PAMELA results, can consistently be fitted within a unique diffusion-reacceleration model. The requirement that light nuclei and $\bar p$ data are consistently reproduced within experimental uncertainties places significant limits on the main propagation parameters. In particular, we find the allowed range of the diffusion coefficient spectral index to be $0.3 < δ< 0.6$ at 95% confidence level and that Kraichnan type diffusion is favored with respect to Kolmogorov. While some amount of reacceleration is required, only a limited range of the Alfvén velocity value ($10 \simleq v_A \simleq 20 \km \s^{-1}$) is allowed by a combined analysis of nuclear and antiproton data, which we perform here for the first time. If antiproton data are not used to constrain the propagation parameters, a larger set of models is allowed. In this case, we determine which combinations of the relevant parameters maximize and minimize the antiproton flux under the condition of still fitting light nuclei data at 95% C.L. These models may then be used to constrain a possible extra antiproton component arising from astrophysical or exotic sources (e.g. dark matter annihilation or decay).

astro-ph.HE↗

arXiv2010

Ultra high energy photons as probes of Lorentz symmetry violations in stringy space-time foam models

The time delays between gamma-rays of different energies from extragalactic sources have often been used to probe quantum gravity models in which Lorentz symmetry is violated. It has been claimed that these time delays can be explained by or at least put the strongest available constraints on quantum gravity scenarios that cannot be cast within an effective field theory framework, such as the space-time foam, D-brane model. Here we show that this model would predict too many photons in the ultra-high energy cosmic ray flux to be consistent with observations. The resulting constraints on the space-time foam model are much stronger than limits from time delays and allow for Lorentz violations effects way too small for explaining the observed time delays.

astro-ph.HE↗

arXiv2010

Constraining Decaying Dark Matter with Fermi LAT Gamma-rays

High energy electrons and positrons from decaying dark matter can produce a significant flux of gamma rays by inverse Compton off low energy photons in the interstellar radiation field. This possibility is inevitably related with the dark matter interpretation of the observed PAMELA and FERMI excesses. The aim of this paper is providing a simple and universal method to constraint dark matter models which produce electrons and positrons in their decay by using the Fermi LAT gamma-ray observations in the energy range between 0.5 GeV and 300 GeV. We provide a set of universal response functions that, once convolved with a specific dark matter model produce the desired constraint. Our response functions contain all the astrophysical inputs such as the electron propagation in the galaxy, the dark matter profile, the gamma-ray fluxes of known origin, and the Fermi LAT data. We study the uncertainties in the determination of the response functions and apply them to place constraints on some specific dark matter decay models that can well fit the positron and electron fluxes observed by PAMELA and Fermi LAT. To this end we also take into account prompt radiation from the dark matter decay. We find that with the available data decaying dark matter cannot be excluded as source of the PAMELA positron excess.

astro-ph.HE↗

arXiv2010

Possible cosmogenic neutrino constraints on Planck-scale Lorentz violation

We study, within an effective field theory framework, $O(E^{2}/\Mpl^{2})$ Planck-scale suppressed Lorentz invariance violation (LV) effects in the neutrino sector, whose size we parameterize by a dimensionless parameter $η_ν$. We find deviations from predictions of Lorentz invariant physics in the cosmogenic neutrino spectrum. For positive O(1) coefficients no neutrino will survive above $10^{19} \eV$. The existence of this cutoff generates a bump in the neutrino spectrum at energies of $10^{17} \eV$. Although at present no constraint can be cast, as current experiments do not have enough sensitivity to detect ultra-high-energy neutrinos, we show that experiments in construction or being planned have the potential to cast limits as strong as $η_ν \lesssim 10^{-4}$ on the neutrino LV parameter, depending on how LV is distributed among neutrino mass states. Constraints on $η_ν < 0$ can in principle be obtained with this strategy, but they require a more detailed modeling of how LV affects the neutrino sector.

hep-ph↗

arXiv2009

Planck-scale Lorentz violation constrained by Ultra-High-Energy Cosmic Rays

We investigate the consequences of higher dimension Lorentz violating, CPT even kinetic operators that couple standard model fields to a non-zero vector field in an Effective Field Theory framework. Comparing the ultra-high energy cosmic ray spectrum reconstructed in the presence of such terms with data from the Pierre Auger observatory allows us to establish two sided bounds on the coefficients of the mass dimension five and six operators for the proton and pion. Our bounds imply that for both protons and pions, the energy scale of Lorentz symmetry breaking must be well above the Planck scale. In particular, the dimension five operators are constrained at the level of $10^{-3} M_{\rm Planck}^{-1}$. The magnitude of the dimension six proton coefficient is bounded at the level of $10^{-6} M_{Planck}^{-2}$ except in a narrow range where the pion and proton coefficients are both negative and nearly equal. In this small area, the magnitude of the dimension six proton coefficient must only be below $10^{-3} M_{\rm Planck}^{-2}$. Constraints on the dimension six pion coefficient are found to be much weaker, but still below $M_{\rm Planck}^{-2}$.

astro-ph.HE↗

arXiv2009

Lorentz Violation: Motivation and new constraints

We review the main theoretical motivations and observational constraints on Planck scale suppressed violations of Lorentz invariance. After introducing the problems related to the phenomenological study of quantum gravitational effects, we discuss the main theoretical frameworks within which possible departures from Lorentz invariance can be described. In particular, we focus on the framework of Effective Field Theory, describing several possible ways of including Lorentz violation therein and discussing their theoretical viability. We review the main low energy effects that are expected in this framework. We discuss the current observational constraints on such a framework, focusing on those achievable through high-energy astrophysics observations. In this context we present a summary of the most recent and strongest constraints on QED with Lorentz violating non-renormalizable operators. Finally, we discuss the present status of the field and its future perspectives.

astro-ph.HE↗

arXiv2008

Gamma-ray polarization constraints on Planck scale violations of special relativity

Using recent polarimetric observations of the Crab Nebula in the hard X-ray band by INTEGRAL, we show that the absence of vacuum birefringence effects constrains O(E/M) Lorentz violation in QED to the level |ξ| < 9x10^{-10} at three sigma CL, tightening by more than three orders of magnitude previous constraints. We show that planned X-ray polarimeters have the potential the potential to probe |ξ|~ 10^{-16} by detecting polarization in active galaxies at red-shift ~1.

astro-ph↗

arXiv2008

GZK photon constraints on Planck scale Lorentz violation in QED

We show how the argument exploited by Galaverni & Sigl in Phys. Rev. Lett., 100, 021102 (2008) (see also arXiv:0708.1737) to constrain Lorentz invariance violation (LV) using Ultra-High-Energy photon non observation by the AUGER experiment, can be extended to QED with Planck-suppressed LV (at order $O(E/M)$ and $O(E^2/M^2)$). While the original constraints given by Galaverni & Sigl happen to be weakened, we show that, when used together with other EFT reactions and the expected detection of photons at $E > 10^{19}$ eV by AUGER, this method has the potentiality not only to basically rule out order $O(E/M)$ corrections but also to strongly constrain, for the first time, the CPT-even $O(E^2/M^2)$ LV QED.

astro-ph↗

arXiv2007

New constraints on Planck-scale Lorentz Violation in QED from the Crab Nebula

We set constraints on O(E/M) Lorentz Violation in QED in an effective field theory framework. A major consequence of such assumptions is the modification of the dispersion relations for electrons/positrons and photons, which in turn can affect the electromagnetic output of astrophysical objects. We compare the information provided by multiwavelength observations with a full and self-consistent computation of the broad-band spectrum of the Crab Nebula. We cast constraints of order 10^{-5} at 95% confidence level on the lepton Lorentz Violation parameters.

astro-ph↗

arXiv2007

Diffuse Neutrino and Gamma-ray Emissions of the Galaxy above the TeV

We simulate the neutrino and $γ$-ray emissions of the Galaxy which are originated from the hadronic scattering of cosmic rays (CR) with the interstellar medium (ISM). Rather than assuming a uniform CR density, we estimate the spatial distribution of CR nuclei by means of numerical simulations. We consider several models of the galactic magnetic field and of the ISM distribution finding only a weak dependence of our results on their choice. We found that by extrapolating the predicted $γ$-ray spectra down to few GeV we get a good agreement with EGRET measurements. Then, we can reliably compare our predictions with available observations above the TeV both for the $γ$-rays and the neutrinos. We confirm that the excesses observed by MILAGRO in the Cygnus region and by HESS in the Galactic Centre Ridge cannot be explained without invoking significant CR over-densities in those regions. Finally, we discuss the perspectives that a km$^3$ neutrino telescope based in the North hemisphere has to measure the diffuse emission from the inner Galaxy.

astro-ph↗

arXiv2006

TeV Neutrinos from SuperNova Remnants embedded in Giant Molecular Clouds

The recent detection of $γ$-rays with energy up to 10 TeV from dense regions surrounding some Supernova Remnants (SNR) provides strong, though still not conclusive, evidence that the nucleonic component of galactic Cosmic Rays is accelerated in the supernova outflows. Neutrino telescopes could further support the validity of such scenario by detecting neutrinos coming from the same regions. We re-evaluate the TeV range neutrino-photon flux ratio to be expected from pion decay, finding small differences respect to previous derivations. We apply our results and the recent HESS measurements of the very high energy $γ$-ray flux from the molecular cloud complex in the Galactic Centre, to estimate the neutrino flux from that region discussing the detectability perspectives for Mediterranean Neutrino Telescopes. We also discuss under which conditions neutron decay may give rise to a significant TeV antineutrino flux from a SNR embedded in Molecular Cloud complexes.

astro-ph↗

arXiv2005

Sgr A East as a possible high energy neutron factory in the Galactic Centre

Sgr A East is a supernova remnant located within few parsecs from the Galactic Centre (GC). There are good reasons to believe that this object is the source of the gamma-ray excess detected by HESS in the direction of the GC meaning that Sgr A East is likely to be an efficient Cosmic Ray accelerator. Some observations suggest that strong magnetic fields may be present in that region allowing the acceleration of composite nuclei in Sgr A East beyond the EeV. We show that, if this is case, EeV neutrons should be effectively produced by the photo-disintegration of Ultra High Energy nuclei onto the IR photon background (with temperature $\sim 40$ K) in which Sgr A East is embedded. Neutrons with such an energy can reach the Earth before decaying and may be detectable under the form of a CR point-like excess in the direction of the GC. We determine the expected energy spectrum and the amplitude of this signal showing that it may be measurable by the AUGER observatory.

astro-ph↗