There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

We review in detail a number of approaches that have been adopted to try and explain the remarkable observation of our accelerating universe. In particular we discuss the arguments for and recent progress made towards understanding the nature of dark energy. We review the observational evidence for the current accelerated expansion of the universe and present a number of dark energy models in addition to the conventional cosmological constant, paying particular attention to scalar field models such as quintessence, K-essence, tachyon, phantom and dilatonic models. The importance of cosmological scaling solutions is emphasized when studying the dynamical system of scalar fields including coupled dark energy. We study the evolution of cosmological perturbations allowing us to confront them with the observation of the Cosmic Microwave Background and Large Scale Structure and demonstrate how it is possible in principle to reconstruct the equation of state of dark energy by also using Supernovae Ia observational data. We also discuss in detail the nature of tracking solutions in cosmology, particle physics and braneworld models of dark energy, the nature of possible future singularities, the effect of higher order curvature terms to avoid a Big Rip singularity, and approaches to modifying gravity which leads to a late-time accelerated expansion without recourse to a new form of dark energy.

Dynamics of dark energy

On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

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The Observation of Gravitational Waves from a Binary Black Hole Merger

Lorenzo Amati1,2, Alan Cosimo Ruggeri3,4, Giulia Stratta5, Salvatore Capozziello3,4, Mariafelicia De Laurentis3,4, Massimo Della Valle2,6, Orlando Luongo3,4 1INAF IASF Bologna, via P. Gobetti 101, Bologna (Italy) 2ICRANet, Piazzale della Repubblica 10, Pescara (Italy) 3Università di Napoli Federico II, Via Cinthia, Napoli (Italy) 4INFN Sez. di Napoli, Monte S. Angelo, Via Cinthia, Napoli (Italy) 5Universitá degli Studi di Urbino "Carlo Bo", Urbino (Italy) 6INAF Osservatorio di Capodimonte, Salita Moiariello 16, Napoli (Italy) E-mail: amati@iasfbo.inaf.it

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The SKA contribution to GRB cosmology

The construction of algebraic structure of central molecular chirality is provided starting from the empirical Fischer projections for tetrahedrons. A matrix representation is given and the algebra of O(4) orthogonal group for rotations and inversions is identified. The result can be generalized to chains of connected tetrahedrons.

Algebraic structure of central molecular chirality starting from Fischer projections

We investigate (n + 1) -dimensional string-dilaton cosmology with an effective dilaton potential in the presence of perfect-fluid matter. We obtain exact solutions parametrized by the constant γ of the equation of state p =( γ −1)ρ , the spatial dimension n , the density of matter, and the spatial curvature constant k . Furthermore, we derive the Wheeler–DeWitt equation and discuss the wave function of the Universe. Finally, the recovering of ordinary Einstein gravity, starting from a string-dominated regime, is discussed. A sort of asymptotic freedom, due to string effective coupling, emerges from the dynamics.

Perfect fluids in string dilaton cosmology.

Loop Quantum Cosmology (LQC) is a theory which renders the Big Bang initial singularity into a quantum bounce, by means of short range repulsive quantum effects at the Planck scale. In this work, we are interested in reproducing the effective Friedmann equation of LQC, by considering a generic $f(R,P,Q)$ theory of gravity, where $R=g^{\mu\nu}R_{\mu\nu}$ is the Ricci scalar, $P=R_{\mu\nu}R^{\mu\nu}$, and $Q=R_{\alpha\beta\mu\nu}R^{\alpha\beta\mu\nu}$ is the Kretschmann scalar. An order reduction technique allows us to work in $f(R,P,Q)$ theories which are perturbatively close to General Relativity, and to deduce a modified Friedmann equation in the reduced theory. Requiring that the modified Friedmann equation mimics the effective Friedmann equation of LQC, we are able to derive several functional forms of $f(R,P,Q)$. We discuss the necessary conditions to obtain viable bouncing cosmologies for the proposed effective actions of $f(R,P,Q)$ theory of gravity.

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Effective actions for loop quantum cosmology in fourth-order gravity

$f(Q)$ symmetric-teleparallel gravity is considered in view of Quantum Cosmology. Specifically, we derive cosmological equations for $f(Q)$ models and then investigate the related energy conditions. In the minisuperspace formalism, the point-like $f(Q)$ Hamiltonian is taken into account. In this framework, we obtain and solve the Wheeler-De Witt equation, thus finding the Wave Function of the Universe in different cases. We show that the Hartle Criterion can be applied and classical observable universes occur. 

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Salvatore Capozziello

Papers

The SKA contribution to GRB cosmology

Algebraic structure of central molecular chirality starting from Fischer projections

Perfect fluids in string dilaton cosmology.

Effective actions for loop quantum cosmology in fourth-order gravity

Minisuperspace quantum cosmology in f(Q) gravity