Neutron star solutions with curvature induced scalarization in the extended Gauss-Bonnet scalar-tensor theories [CL]

In the present paper we study models of neutron stars in a class of extended scalar-tensor Gauss-Bonnet (ESTGB) theories for which the scalar degree of freedom is exited only in the strong curvature regime. We show that in the framework of the ESTGB theories under consideration there exist new neutron star solutions which are formed via spontaneous scalarization of the general relativistic neutron stars. In contrast to the spontaneous scalarization in the standard scalar-tensor theories which is induced by the presence of matter, in our case the scalarization is induced by the spacetime curvature.

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D. Doneva and S. Yazadjiev
Tue, 12 Dec 17

Comments: 12 pages, 5 figures

Conformal Higgs Gravity [CL]

It is shown that gravitation emerges naturally from the standard model of particle physics if local scale invariance is imposed in the context of a single conformal theory. Doing so resolves major puzzles afflicting the standard models of particle physics and cosmology, clearly indicating these to be artifacts stemming from universally applying the system of units selected here and now. Slip-free scalar (but not vector or tensor) modes of metric perturbations can be gauged away and are thus spurious degrees of freedom. In the approach adopted here gravitation is viewed as a collective phenomenon, with its characteristic Planck scale devoid of fundamental meaning; consequently, mass hierarchy and Higgs mass instability concerns are avoided altogether. On cosmological scales, the dynamical vacuum-like Higgs self-coupling energy accounts for dark energy, and its near equality with nonrelativistic matter is simply a result of the choice of standard units.

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M. Shimon
Tue, 12 Dec 17

Comments: Submitted for publication

Late time afterglow observations reveal a collimated relativistic jet in the ejecta of the binary neutron star merger GW170817 [HEAP]

The binary neutron star (BNS) merger GW170817 was the first astrophysical source detected in gravitational waves and multi-wavelength electromagnetic radiation. The almost simultaneous observation of a pulse of gamma-rays proved that BNS mergers are associated with at least some short gamma-ray bursts (GRBs). However, the gamma-ray pulse was faint, casting doubts on the association of BNS mergers with the luminous, highly relativistic outflows of canonical short GRBs. Here we show that structured jets with a relativistic, energetic core surrounded by slower and less energetic wings produce afterglow emission that brightens characteristically with time, as recently seen in the afterglow of GW170817. Initially, we only see the relatively slow material moving towards us. As time passes, larger and larger sections of the outflow become visible, increasing the luminosity of the afterglow. The late appearance and increasing brightness of the multi-wavelength afterglow of GW170817 allow us to constrain the geometry of its ejecta and thus reveal the presence of an off-axis jet pointing about 20 degrees away from Earth. Our results confirm a single origin for BNS mergers and short GRBs: GW170817 produced a structured outflow with a highly relativistic core and a canonical short GRB. We did not see the bright burst because it was beamed away from Earth. However, approximately one in 20 mergers detected in gravitational waves will be accompanied by a bright, canonical short GRB.

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D. Lazzati, R. Perna, B. Morsony, et. al.
Tue, 12 Dec 17

Comments: 24 pages, 3 figures (main text), 7 figures (methods) and 1 table

The Evens and Odds of CMB Anomalies [CEA]

The lack of power of large–angle CMB anisotropies is known to increase its statistical significance at higher Galactic latitudes, where a string–inspired pre–inflationary scale $\Delta$ can also be detected. Considering the Planck 2015 data, and relying largely on a Bayesian approach, a novelty for CMB anomalies, we show that the effect is mostly driven by the \emph{even}–$\ell$ harmonic multipoles with $\ell \lesssim 20$, which appear sizably suppressed in a way that is robust with respect to Galactic masking, along with the corresponding detections of $\Delta$. On the other hand, the first \emph{odd}–$\ell$ multipoles are only suppressed at high Galactic latitudes. We investigate this behavior in different sky masks, constraining $\Delta$ through even and odd multipoles, and we elaborate on possible implications. We include systematically low–$\ell$ polarization data, which are currently noise limited and yet help in attaining confidence levels of about 3 $\sigma$ in the detection of $\Delta$. We also show by direct forecasts that a future all–sky $E$–mode cosmic–variance–limited polarization survey may push the constraining power for $\Delta$ beyond 5 $\sigma$.

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A. Gruppuso, N. Kitazawa, M. Lattanzi, et. al.
Tue, 12 Dec 17

Comments: 49 pages, 20 figures

J1342+0928 Confirms the Cosmological Timeline in R_h=ct [CEA]

The discovery of quasar J1342+0928 (z=7.54) reinforces the time compression problem associated with the premature formation of structure in LCDM. Adopting the Planck parameters, we see this quasar barely 690 Myr after the big bang, no more than several hundred Myr after the transition from Pop III to Pop II star formation. Yet conventional astrophysics would tell us that a 10 M_sol seed, created by a Pop II/III supernova, should have taken at least 820 Myr to grow via Eddington-limited accretion. This failure by LCDM constitutes one of its most serious challenges, requiring exotic `fixes’, such as anomalously high accretion rates, or the creation of enormously massive (~10^5 M_sol) seeds, neither of which is ever seen in the local Universe, or anywhere else for that matter. Indeed, to emphasize this point, J1342+0928 is seen to be accreting at about the Eddington rate, negating any attempt at explaining its unusually high mass due to such exotic means. In this Letter, we demonstrate that the discovery of this quasar instead strongly confirms the cosmological timeline predicted by the R_h=ct universe. In this model, a 10 M_sol seed at z ~ 15 (the start of the Epoch of Reionization at t ~ 878 Myr) would have easily grown into an 8 x 10^8 M_sol black hole at z=7.54 (t ~ 1.65 Gyr) via conventional Eddington-limited accretion.

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F. Melia
Tue, 12 Dec 17

Comments: 9 pages, 1 figure

What can we learn from the stochastic gravitational wave background produced by oscillons? [CEA]

The stochastic gravitational wave (GW) background provides a fascinating window to the physics of the very early universe. Beyond the nearly scale-invariant primordial GW spectrum produced during inflation, a spectrum with a much richer structure is typically generated during the preheating phase after inflation (or after some other phase transition at lower energies). This raises the question of what one can learn from a future observation of the stochastic gravitational wave background spectrum about the underlying physics during preheating. Recently, it has been shown that during preheating non-perturbative quasi-stable objects like oscillons can act as strong sources for GW, leading to characteristic features such as distinct peaks in the spectrum. In this paper, we study the GW production from oscillons using semi-analytical techniques. In particular, we discuss how the GW spectrum is affected by the parameters that characterise a given oscillon system, e.g. by the background cosmology, the asymmetry of the oscillons and the evolution of the number density of the oscillons. We compare our semi-analytic results with numerical lattice simulations for a hilltop inflation model and a KKLT scenario, which differ strongly in some of these characteristics, and find very good agreement.

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S. Antusch, F. Cefala and S. Orani
Tue, 12 Dec 17

Comments: 25 pages + Appendix, 16 figures

The MSSM inflation and cosmological attractors [CL]

Inflationary scenarios motivated by the Minimal Supersymmetric Standard Model (MSSM) where five scalar fields are non-minimally coupled to gravity are considered. The potential of the model and the function of non-minimal coupling are polynomials of two Higgs doublet convolutions. We show that the use of the strong coupling approximation allows to obtain inflationary parameters in the case when a combination of the four scalar fields plays a role of inflaton. Numerical calculations show that the cosmological evolution leads to inflationary scenarios fully compatible with observational data for different values of the MSSM mixing angle $\beta$.

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M. Dubinin, E. Petrova, E. Pozdeeva, et. al.
Tue, 12 Dec 17

Comments: 13 pages, 1 figure. arXiv admin note: text overlap with arXiv:1705.09624