118578178
Observations of very high energy gamma-ray emission from AGNs with the ground-based EAS arrays
The ground-based EAS array is usually operated with a high duty cycle (> 90%) and a large field of view (∼ 2sr), which can continuously monitor the sky. It is essential and irreplaceable to understand the gamma-ray emission mechanism and intrinsic physics progress of the variable source AGN. The EAS arrays, AS-γ experiment (since 1990) and ARGO-YBJ experiment (since 2007), have continuously monitored the northern sky at energies above 3 TeV and 0.3 TeV, respectively. They have made substantial contributions for long-term monitoring of Mrk 421 and Mrk 501. In this paper, we will review the results obtained by the EAS arrays. The next generation of EAS array, LHAASO project, will boost the sensitivity of current EAS array at least up to 30 times with a much wider energy range from 40 GeV to 1 PeV. Beside increasing the number of VHE gamma-ray sources, it will guide us look sight into the properties of jet, and throw light on the determining of the EBL, intergalactic magnetic fields, and the validity of the Lorentz Invariance.
117323209
Search for GRB counterparts using the ARGO‐YBJ experiment in shower mode
In this paper, the effective area of the ARGO‐YBJ experiment to detect the gamma rays with energy range from 10 GeV to 1 TeV for different incident zenith angles (0,10,20,30,40 degrees) is given respectively. The optimal event selections to search for GRB counterparts with different cutoff energy models (Ecut = 100 GeV and 1 TeV) are studied. Using these selections and their corresponding angular resolutions the searches are done within two hours around the GRB trigger time via different time windows. Finally, the result for the 20 GRBs in the field of view of ARGO between July 2006 and July 2008 is presented, and the fluence upper limit for each GRB is set at 99% confidence level.
115310371
Preliminary results of the Moon shadow with ARGO-YBJ
55209539
Characteristic Plane Method with Conical Correction
In ground-based cosmic ray experiments, the equalization of the transit time of signals coming from different parts of the apparatus is of crucial importance for the improvement of the angular resolution and accuracy. In the ARGO-YBJ experiment, this is achieved using the Characteristic Plane Method with conical correction, studied by both Monte Carlo simulation and real data and also checked with manual absolute calibration on a portion of the detector. By introducing conical correction in primary direction reconstruction, the systematics error existing in the off-line calibration with planar fit is successfully removed. Two subsequent construction phases of the detector have been considered: ARGO-42 and ARGO-104. During the calibration of ARGO-104, events with more than 1000 hits and with the core reconstructed inside the carpet were used in order to achieve a good reconstruction of the shower, that is the arrival direction and the core position. The results of the calibration concerning the two configurations, ARGO-42 and ARGO-104, are compared and discussed.
118413139
TeV gamma-ray survey of the northern sky using the ARGO-YBJ experiment
The ARGO-YBJ experiment is an extensive air shower array that monitored the northern g-ray sky at energies above 0.3 TeV from 2007 November to 2013 January. In this paper we present the result of a sky survey in the declination band from -10 ◦ to 70 ◦ , using the data recorded in more than five years. With a cumulative sensitivity ranging from 0.24 to ∼1 Crab units, depending on the declination, six sources have been observed with a statistical significance greater than 5 standard deviations. Several interesting hotspots are also reported as potential g-ray emitters. The features of each source are presented and discussed. Additionally, 95% confidence level upper limits to the flux from all sky regions are presented, which are more stringent than any previously published limits for TeV g-ray all-sky surveys. The specific upper limits for 663 GeV g-ray AGNs inside the ARGO-YBJ field of view are presented. The effect of the absorbtion of g-rays due to the interaction with the extragalactic background light are estimated.
11090952
Cosmic ray threshold anomaly and kinematics in the dS spacetime
We present a covariant framework of kinematics in the dS spacetime, which is a natural postulate of recent astronomical observations ($\Lambda>0)$. One-particle states are presented explicitly. It is noticed that the dispersion relation of free particles is dependent on the degrees of freedom of angular momentum and spin. This fact can be referred to as the effects of the cosmological constant on kinematics of particles. The kinematics in dS spacetime is used to investigate the phenomenon of ultra high energy cosmic rays. We emphasize the possibility of solving the threshold anomalies of the interactions between ultra high energy cosmic rays and soft photons in the covariant framework of kinematics in the dS spacetime.
118839273
Cosmological perturbations in f(T) gravity
We investigate the cosmological perturbations in f(T) gravity. Examining the pure gravitational perturbations in the scalar sector using a diagonal vierbein, we extract the corresponding dispersion relation, which provides a constraint on the f(T) Ansaetze that lead to a theory free of instabilities. Additionally, upon inclusion of the matter perturbations, we derive the fully perturbed equations of motion, and we study the growth of matter overdensities. We show that f(T) gravity with f(T) constant coincides with General Relativity, both at the background as well as at the first-order perturbation level. Applying our formalism to the power-law model we find that on large subhorizon scales (O(100 Mpc) or larger), the evolution of matter overdensity will differ from {Lambda}CDM cosmology. Finally, examining the linear perturbations of the vector and tensor sectors, we find that (for the standard choice of vierbein) f(T) gravity is free of massive gravitons.
119109295
Collision of two general geodesic particles around a Kerr-Newman black hole
We study collision of two general geodesic particles around the Kerr-Newman (KN) black hole and get the center-of-mass (CM) energy of the non-marginally and marginally bound critical particles in the direct collision and LSO collision scenarios. We find the constraint conditions that arbitrarily high CM energy can be obtained for the near-horizon collision of two general geodesic particles in the extremal KN black hole, and note that the charge decreases the value of the latitude in which arbitrarily high CM energy can occurs. We also interpret why the high-velocity collision belt centers to the equator with the increase of the charge.
118374075
A new approach to the vacuum of inflationary models
A new approach is given for the implementation of boundary conditions used in solving the Mukhanov–Sasaki equation in the context of inflation. The familiar quantization procedure is reviewed, along with a discussion of where one might expect deviations from the standard approach to arise. The proposed method introduces a (model-dependent) fitting function for the z″/z and a″/a terms in the Mukhanov–Sasaki equation for scalar and tensor modes, as well as imposes the boundary conditions at a finite conformal time. As an example, we employ a fitting function and compute the spectral index, along with its running, for a specific inflationary model, which possesses background equations that are analytically solvable. The observational upper bound on the tensor to scalar ratio is used to constrain the parameters of the boundary conditions in the tensor sector as well. An overview on the generalization of this method is also discussed.
118567951
Phantom scalar emission in the Kerr black hole spacetime
We study the absorption probability and Hawking radiation spectra of a phantom scalar field in the Kerr black hole spacetime. We find that the presence of negative kinetic energy terms modifies the standard results in the graybody factor, super-radiance and Hawking radiation. Comparing with the usual scalar particle, the phantom scalar emission is enhanced in the black hole spacetime.