Yasunori Nomura, Nico Salzetta

The firewall paradox for black holes is often viewed as indicating a conflict between unitarity and the equivalence principle. We elucidate how the paradox manifests as a limitation of semiclassical theory, rather than presents a conflict between fundamental principles. Two principal features of the fundamental and semiclassical theories address two versions of the paradox: the entanglement and typicality arguments. First, the number of physical configurations representing semiclassical excitations is exponentially smaller than that given by the Bekenstein-Hawking entropy. Second, despite the smallness of the Hilbert space for physical excitations, the semiclassical theory possesses an unphysically large Fock space built by creation and annihilation operators on a fixed black hole background. Understanding these features not only eliminates the necessity of firewalls but also leads to a new picture of Hawking emission contrasting pair creation at the horizon.

Alberto Sesana

We show that the black hole binary (BHB) coalescence rates inferred from the advanced LIGO (aLIGO) detection of GW150914 imply an unexpectedly loud GW sky at milli-Hz frequencies accessible to the evolving Laser Interferometer Space Antenna (eLISA), with several outstanding consequences. First, up to thousands of BHB will be individually resolvable by eLISA; second, millions of non resolvable BHBs will build a confusion noise detectable with signal-to-noise ratio of few to hundreds; third -- and perhaps most importantly -- up to hundreds of BHBs individually resolvable by eLISA will coalesce in the aLIGO band within ten years. eLISA observations will tell aLIGO and all electromagnetic probes weeks in advance when and where these BHB coalescences are going to occur, with uncertainties of <10s and <1deg^2. This will allow the pre-pointing of telescopes to realize coincident GW and multi-wavelength electromagnetic observations of BHB mergers. Time coincidence is critical because prompt emission associated to a BHB merger will likely have a duration comparable to the dynamical time-scale of the systems, and is only possible with low frequency GW alerts.

Nicolas B. Cowan, Gil Holder, Nathan A. Kaib

Cosmology experiments at mm-wavelengths may be able to detect Planet Nine if it is the size of Neptune, has an effective temperature of 40 K, and is 700 AU from the Sun. It would appear as a ~30 mJy source at 1 mm (or ~8 mJy at 150 GHz) with a parallax of ~5 arcmin. The challenge will be to distinguish it from the ~4000 foreground asteroids brighter than 30 mJy. Fortunately, asteroids can by identified by looking for sources that move across a resolution element in a matter of hours, orders of magnitude faster than Planet Nine. If Planet Nine is smaller, colder, and/or more distant than expected, then it could be as faint as 1 mJy at 1 mm. There are approximately 1E6 asteroids this bright, making many cosmology experiments confusion limited for moving sources. Nonetheless, it may still be possible to find the proverbial needle in the haystack using a matched filter. This would require mm telescopes with high angular resolution and high sensitivity in order to alleviate confusion and to enable the identification of moving sources with relatively short time baselines. Regardless of its mm flux density, searching for Planet Nine would entail obtaining frequent radio measurements for large swaths of the sky, including the ecliptic and Galactic plane. Even if Planet Nine had already been detected by other means, measuring its mm-flux would constrain its internal energy budget, and therefore help resolve the mystery of Uranus and Neptune, which have vastly different internal heat.

Stephon Alexander, John D. Barrow, Joao Magueijo

We investigate how a Higgs mechanism could be responsible for the emergence of gravity in extensions of Einstein theory. In this scenario, at high energies, symmetry restoration could "turn off" gravity, with dramatic implications for cosmology and quantum gravity. The sense in which gravity is muted depends on the details of the implementation. In the most extreme case gravity's dynamical degrees of freedom would only be unleashed after the Higgs field acquires a non-trivial vacuum expectation value, with gravity reduced to a topological field theory in the symmetric phase. We might also identify the Higgs and the Brans-Dicke fields in such a way that in the unbroken phase Newton's constant vanishes, decoupling matter and gravity. We discuss the broad implications of these scenarios.

Daya Bay Collaboration F. P. An A. B. Balantekin H. R. Band M. Bishai S. Blyth I. Butorov D. Cao G. F. Cao J. Cao W. R. Cen Y. L. Chan J. F. Chang L. C. Chang Y. Chang H. S. Chen Q. Y. Chen S. M. Chen Y. X. Chen Y. Chen J. H. Cheng J. Cheng Y. P. Cheng J. J. Cherwinka M. C. Chu J. P. Cummings J. de Arcos Z. Y. Deng X. F. Ding Y. Y. Ding M. V. Diwan J. Dove E. Draeger D. A. Dwyer W. R. Edwards S. R. Ely R. Gill M. Gonchar G. H. Gong H. Gong M. Grassi W. Q. Gu M. Y. Guan L. Guo X. H. Guo R. W. Hackenburg R. Han S. Hans M. He K. M. Heeger Y. K. Heng A. Higuera Y. K. Hor Y. B. Hsiung B. Z. Hu L. M. Hu L. J. Hu T. Hu W. Hu E. C. Huang H. X. Huang X. T. Huang P. Huber G. Hussain D. E. Jaffe P. Jaffke K. L. Jen S. Jetter X. P. Ji X. L. Ji J. B. Jiao R. A. Johnson L. Kang S. H. Kettell S. Kohn M. Kramer K. K. Kwan M. W. Kwok T. Kwok T. J. Langford K. Lau L. Lebanowski J. Lee R. T. Lei R. Leitner K. Y. Leung J. K. C. Leung C. A. Lewis D. J. Li F. Li G. S. Li Q. J. Li S. C. Li W. D. Li X. N. Li X. Q. Li Y. F. Li Z. B. Li H. Liang C. J. Lin G. L. Lin P. Y. Lin S. K. Lin J. J. Ling J. M. Link L. Littenberg B. R. Littlejohn D. W. Liu H. Liu J. L. Liu J. C. Liu S. S. Liu C. Lu H. Q. Lu J. S. Lu K. B. Luk Q. M. Ma X. Y. Ma X. B. Ma Y. Q. Ma D. A. Martinez Caicedo K. T. McDonald R. D. McKeown Y. Meng I. Mitchell J. Monari Kebwaro Y. Nakajima J. Napolitano D. Naumov E. Naumova H. Y. Ngai Z. Ning J. P. Ochoa-Ricoux A. Olshevski H. -R. Pan J. Park S. Patton V. Pec J. C. Peng L. E. Piilonen L. Pinsky C. S. J. Pun F. Z. Qi M. Qi X. Qian N. Raper B. Ren J. Ren R. Rosero B. Roskovec X. C. Ruan B. B. Shao H. Steiner G. X. Sun J. L. Sun W. Tang D. Taychenachev K. V. Tsang C. E. Tull Y. C. Tung N. Viaux B. Viren V. Vorobel C. H. Wang M. Wang N. Y. Wang R. G. Wang W. Wang W. W. Wang X. Wang Y. F. Wang Z. Wang Z. Wang Z. M. Wang H. Y. Wei L. J. Wen K. Whisnant C. G. White L. Whitehead T. Wise H. L. H. Wong S. C. F. Wong E. Worcester Q. Wu D. M. Xia J. K. Xia X. Xia Z. Z. Xing J. Y. Xu J. L. Xu J. Xu Y. Xu T. Xue J. Yan C. G. Yang L. Yang M. S. Yang M. T. Yang M. Ye M. Yeh B. L. Young G. Y. Yu Z. Y. Yu S. L. Zang L. Zhan C. Zhang H. H. Zhang J. W. Zhang Q. M. Zhang Y. M. Zhang Y. X. Zhang Y. M. Zhang Z. J. Zhang Z. Y. Zhang Z. P. Zhang J. Zhao Q. W. Zhao Y. F. Zhao Y. B. Zhao L. Zheng W. L. Zhong L. Zhou N. Zhou H. L. Zhuang J. H. Zou

This Letter reports a measurement of the flux and energy spectrum of electron antineutrinos from six 2.9~GW$_{th}$ nuclear reactors with six detectors deployed in two near (effective baselines 512~m and 561~m) and one far (1,579~m) underground experimental halls in the Daya Bay experiment. Using 217 days of data, 296,721 and 41,589 inverse beta decay (IBD) candidates were detected in the near and far halls, respectively. The measured IBD yield is (1.55 $\pm$ 0.04) $\times$ 10$^{-18}$~cm$^2$/GW/day or (5.92 $\pm$ 0.14) $\times$ 10$^{-43}$~cm$^2$/fission. This flux measurement is consistent with previous short-baseline reactor antineutrino experiments and is $0.946\pm0.022$ ($0.991\pm0.023$) relative to the flux predicted with the Huber+Mueller (ILL+Vogel) fissile antineutrino model. The measured IBD positron energy spectrum deviates from both spectral predictions by more than 2$\sigma$ over the full energy range with a local significance of up to $\sim$4$\sigma$ between 4-6 MeV. A reactor antineutrino spectrum of IBD reactions is extracted from the measured positron energy spectrum for model-independent predictions.

Alireza Sepehri, Ahmed Farag Ali

Recently, an interesting mechanism [Phys.Rev.Lett.106:231101,2011] has been proposed which produces all nonlinear terms in massive gravity to all orders . In this work, we reproduce these results in M-theory and consider the process of birth and growth of nonlinear gravity during the construction of Mp-branes. It has been shown that Mp brane are built up of p- M1-branes which each of them are connected to M1-branes of other Mp-brane through a wormhole. In this model, by increasing the number of dimensions, the number of nonlinear terms in relevant action of branes enhances and some theories like lovelock and nonlinear gravity are raised. By compacting M-branes, graviton fields in nonlinear gravity converts to photon fields and thus nonlinear electrodynamics are produced.

Lucas Lombriser, Nelson A. Lima

The likely association of a weak short gamma-ray burst observed by the Fermi GBM experiment with the gravitational wave detection GW150914 by the aLIGO instruments implies that self-accelerated Horndeski scalar-tensor theories cannot be linearly shielded. This breaks the dark degeneracy in the large-scale structure that limited a rigorous discrimination between acceleration from modified gravity and from a cosmological constant or dark energy. Signatures of a self-acceleration must therefore manifest in the linear, unscreened cosmological structure. We describe the minimal modification required for self-acceleration and show that its maximum likelihood yields a 2.4-sigma poorer fit to cosmological observations compared to a cosmological constant, which, although marginally still possible, questions the concept of cosmic acceleration from a genuine scalar-tensor modification of gravity.