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Giovanna Dainotti M.,Jagiellonian University | Willingale R.,University of Leicester | Capozziello S.,University of Naples Federico II | Capozziello S.,Complesso Universitario Of Monte Sant Angelo | And 3 more authors.
Astrophysical Journal Letters | Year: 2010

Gamma-ray bursts (GRBs) observed up to redshifts z > 8 are fascinating objects to study due to their still unexplained relativistic outburstmechanisms and their possible use to test cosmological models. Our analysis of 77 GRB afterglows with known redshifts revealed a physical subsample of long GRBs with the canonical plateau breaking to power-law light curves with a significant luminosity L X*-break time T a * correlation in the GRB rest frame. This subsample forms approximately the upper envelope of the studied distribution.We have also found a similar relation for a small sample of GRB afterglows that belong to the intermediate class between the short and the long ones. It proves that within the full sample of afterglows there exist physical subclasses revealed here by tight correlations of their afterglowproperties. The afterglowswith regular ("canonical") light curves obey not only the mentioned tight physical scaling, but-for a given T a * -the more regular progenitor explosions lead to preferentially brighter afterglows. © 2010. The American Astronomical Society. All rights reserved. Source


Basini G.,National Institute of Nuclear Physics, Italy | Capozziello S.,University of Naples Federico II | Capozziello S.,Complesso Universitario Of Monte Sant Angelo | De Laurentis M.,Goethe University Frankfurt | De Laurentis M.,Tomsk State Pedagogical University
International Journal of Geometric Methods in Modern Physics | Year: 2016

Further gravitational massive modes emerge by extending the geometrical sector of Hilbert-Einstein theory in the most general theory including curvature invariants. Besides massless spin-2, also spin-0 and spin-2 massive and ghost fields have to be considered. We investigate the possible detectability of such additional modes by the Large Hadron Collider and calculate the detectable energy density of the spectrum. © 2016 World Scientific Publishing Company. Source


Demianski M.,University of Warsaw | Demianski M.,Williams College | Piedipalumbo E.,University of Naples Federico II | Piedipalumbo E.,Complesso Universitario Of Monte Sant Angelo
Monthly Notices of the Royal Astronomical Society | Year: 2011

The correlation between the peak photon energy of the internal spectrum Ep, i and isotropic equivalent radiated energy Eiso (the Amati relation) is explored in a scalar field model of dark energy. Using an updated data set of 109 high-redshift gamma-ray bursts (GRBs), we show that the correlation parameters only weakly depend on the cosmological model. Once the parameters of the Amati relation have been determined, we use this relation to construct a fiducial GRB Hubble diagram (HD) that extends up to redshifts ~8. Moreover, we apply a local regression technique to estimate, in a model-independent way, the distance modulus from the recently updated Union Type Ia supernova (SNIa) sample, containing 557 SNIa spanning the redshift range of 0.015 ≤z≤ 1.55. The derived calibration parameters are used to construct an updated GRB HD, which we call the calibrated GRB HD. We also compare the fiducial and calibrated GRB HDs, which turned out to be fully statistically consistent, thus indicating that they are not affected by any systematic bias induced by the different calibration procedures. This means that the high-redshift GRBs can be used to test different models of dark energy settling the circularity problem. Furthermore, we investigate possible evolutionary effects that might have important influence on our results. Our analysis indicates that the presently available GRB data sets do not show statistically unambiguous evolutionary effect with the cosmological redshift. Finally, we propose another approach to calibrate the GRB relations, by using an approximate luminosity-distance relation, which holds in any cosmological model. We use this calibration of the Amati relation to construct an empirical approximate HD, which we compare with the calibrated GRB HD. We finally investigate the implications of this approach for the high-redshift cosmography. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source


Dainotti M.G.,Jagiellonian University | Cardone V.F.,University of Molise | Cardone V.F.,University of Naples Federico II | Capozziello S.,University of Naples Federico II | And 3 more authors.
Astrophysical Journal | Year: 2011

Gamma-ray bursts (GRBs) are the most energetic sources in the universe and among the farthest known astrophysical sources. These features make them appealing candidates as standard candles for cosmological applications such that studying the physical mechanisms for the origin of the emission and correlations among their observable properties is an interesting task. We consider here the luminosity L*X andbreak time T*a (hereafter LT) correlation and investigate whether there are systematics induced by selection effects or redshift-dependent calibration. We perform this analysis both for the full sample of 77 Swift GRBs with known redshift and for the subsample of GRBs having canonical X-ray light curves, hereafter called the U0095 sample. We do not find any systematic bias, thus confirming the existence of physical GRB subclasses revealed by tight correlations of their afterglow properties. Furthermore, we study the possibility of applying the LT correlation as a redshift estimator both for the full distribution and for the canonical light curves. The large uncertainties and the non-negligible intrinsic scatter make the results not so encouraging, but there are nevertheless some hints motivating a further analysis with an increased U0095 sample. © 2011. The American Astronomical Society. All rights reserved. Source


Piedipalumbo E.,University of Naples Federico II | Piedipalumbo E.,Complesso Universitario Of Monte Sant Angelo | Della Moglie E.,University of Genoa | Cianci R.,University of Genoa
International Journal of Modern Physics D | Year: 2015

In the last dozen years, a wide and variegated mass of observational data revealed that the universe is now expanding at an accelerated rate. In the absence of a well-based theory to interpret the observations, cosmography provides information about the evolution of the universe from measured distances, only assuming that the geometry can be described by the Friedmann-Lemaitre-Robertson-Walker metric. In this paper, we perform a high-redshift analysis which allows us to put constraints on the cosmographic parameters up to the fifth-order, thus inducing indirect constraints on any gravity theory. Here, we are interested in the so-called teleparallel gravity theory, f(T). Actually, we use the analytical expressions of the present day values of f(T) and its derivatives as functions of the cosmographic parameters to map the cosmography region of confidences into confidence ranges for f(T) and its derivative. Moreover, we show how these can be used to test some teleparallel gravity models without solving the dynamical equations. Our analysis is based on the Union2 Type Ia supernovae (SNIa) data set, a set of 28 measurements of the Hubble parameter, the Hubble diagram constructed from some gamma ray bursts (GRB) luminosity distance indicators and Gaussian priors on the distance from the baryon acoustic oscillations (BAOs) and the Hubble constant h. To perform our statistical analysis and to explore the probability distributions of the cosmographic parameters, we use the Markov chain Monte Carlo (MCMC) method. © World Scientific Publishing Company. Source

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