Barenboim, G., Kinney, W. H., & Morse, M. J. P. (2018). Phantom Dirac-Born-Infeld dark energy. Phys. Rev. D, 98(8), 083531–11pp.
Abstract: Motivated by the apparent discrepancy between cosmic microwave background measurements of the Hubble constant and measurements from Type-la supernovae, we construct a model for dark energy with equation of state w = p/rho < -1, violating the null energy condition. Naive canonical models of so-called “phantom” dark energy require a negative scalar kinetic term, resulting in a Hamiltonian unbounded from below and associated vacuum instability. We construct a scalar field model for dark energy with w < -1, which nonetheless has a Hamiltonian bounded from below in the comoving reference frame, i.e., in the rest frame of the fluid. We demonstrate that the solution is a cosmological attractor, and find that early-time cosmological boundary conditions consist of a “frozen” scalar field, which relaxes to the attractor solution once the dark energy component dominates the cosmological energy density. We consider the model in an arbitrary choice of gauge, and find that, unlike the case of comoving gauge, the fluid Hamiltonian is in fact unbounded from below in the reference frame of a highly boosted observer, corresponding to a nonlinear gradient instability. We discuss this in the context of general NEC-violating perfect fluids, for which this instability is a general property.
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Garcia-Cases, F., Perez-Calatayud, J., Ballester, F., Vijande, J., & Granero, D. (2018). Peripheral dose around a mobile linac for intraoperative radiotherapy: radiation protection aspects. J. Radiol. Prot., 38(4), 1393–1411.
Abstract: The aim of this work is to analyse the scattered radiation produced by the mobile accelerator Mobetron 1000. To do so, detailed Monte Carlo simulations using two different codes, Penelope2008 and Geant4, were performed. Measurements were also done. To quantify the attenuation due to the internal structures, present in the accelerator head, on the scattered radiation produced, some of the main structural shielding in the Mobetron 1000 has been incorporated into the geometry simulation. Results are compared with measurements. Some discrepancies between the calculated and measured dose values were found. These differences can be traced back to the importance of the radiation component due to low energy scattered electrons. This encouraged us to perform additional calculations to separate the role played by this component. Ambient dose equivalent, H*(10), outside of the operating room (OR) has been evaluated using Geant4. H*(10) has been measured inside and outside the OR, being its values compatible with those reported in the literature once the low energy electron component is removed. With respect to the role played by neutrons, estimations of neutron H*(10) using Geant4 together with H*(10) measurements has been performed for the case of the 12 MeV electron beam. The values obtained agree with the experimental values existing in the literature, being much smaller than those registered in conventional accelerators. This study is a useful tool for the clinical user to investigate the radiation protection issues arising with the use of these accelerators in ORs without structural shielding. These results will also enable to better fix the maximum number of treatments that could be performed while insuring adequate radiological protection of workers and public in the hospital.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2018). Performance of missing transverse momentum reconstruction with the ATLAS detector using proton proton collisions at root s=13 TeV. Eur. Phys. J. C, 78(11), 903–46pp.
Abstract: The performance of the missing transverse (E-T(miss) momentum) reconstruction with the ATLAS detector is evaluated using data collected in proton-proton collisions at the LHC at a centre-of-mass energy of 13 TeV in 2015. To reconstruct E-T(miss), fully calibrated electrons, muons, photons, hadronically decaying tau-leptons, and jets reconstructed from calorimeter energy deposits and charged-particle tracks are used. These are combined with the soft hadronic activity measured by reconstructed charged-particle tracks not associated with the hard objects. Possible double counting of contributions from reconstructed charged-particle tracks from the inner detector, energy deposits in the calorimeter, and reconstructed muons from the muon spectrometer is avoided by applying a signal ambiguity resolution procedure which rejects already used signals when combining the various E-T(miss) contributions. The individual terms as well as the overall reconstructed E-T(miss) are evaluated with various performance metrics for scale (linearity), resolution, and sensitivity to the data-taking conditions. The method developed to determine the systematic uncertainties of the E-T(miss) scale and resolution is discussed. Results are shown based on the full 2015 data sample corresponding to an integrated luminosity of 3.2 fb(-1).
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Consiglio, R., de Salas, P. F., Mangano, G., Miele, G., Pastor, S., & Pisanti, O. (2018). PArthENoPE reloaded. Comput. Phys. Commun., 233, 237–242.
Abstract: We describe the main features of a new and updated version of the program PArthENoPE, which computes the abundances of light elements produced during Big Bang Nucleosynthesis. As the previous first release in 2008, the new one, PArthENoPE2.0, is publicly available and distributed from the code site, http://parthenope.na.infn.it . Apart from minor changes, which will be also detailed, the main improvements are as follows. The powerful, but not freely accessible, NAG routines have been substituted by ODEPACK libraries, without any significant loss in precision. Moreover, we have developed a Graphical User Interface (GUI) which allows a friendly use of the code and a simpler implementation of running for grids of input parameters. New Version program summary Program Title: PArthENoPE2.0 Program Files doi : http://dx.doi.org/10.17632/wvgr7d8yt9.1 Licensing provisions: GPLv3 Programming language: Fortran 77 and Python Supplementary material: User Manual available on the web page http://parthenope.na.infn.it Journal reference of previous version: Comput. Phys. Commun. 178 (2008) 956 971 Does the new version supersede the previous version?: Yes Reasons for the new version: Make the code more versatile and user friendly Summary of revisions: (1) Publicly available libraries (2) GUI for configuration Nature of problem: Computation of yields of light elements synthesized in the primordial universe Solution method: Livermore Solver for Ordinary Differential Equations (LSODE) for stiff and nonstiff systems
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Ferreiro, A., & Navarro-Salas, J. (2018). Pair creation in electric fields, anomalies, and renormalization of the electric current. Phys. Rev. D, 97(12), 125012–13pp.
Abstract: We investigate the Schwinger pair production phenomena in spatially homogeneous strong electric fields. We first consider scalar QED in four-dimensions and discuss the potential ambiguity in the adiabatic order assignment for the electromagnetic potential required to fix the renormalization subtractions. We argue that this ambiguity can be solved by invoking the conformal anomaly when both electric and gravitational backgrounds are present. We also extend the adiabatic regularization method for spinor QED in two-dimensions and find consistency with the chiral anomaly. We focus on the issue of the renormalization of the electric current < j(mu)> generated by the created pairs. We illustrate how to implement the renormalization of the electric current for the Sauter pulse.
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