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Sébastien Renaux-Petel, Krzysztof Turzyński
We show the existence of a general mechanism by which heavy scalar fields can be destabilized during inflation, relying on the fact that the curvature of the field space manifold can dominate the stabilizing force from the potential and destabilize inflationary trajectories. We describe a simple and rather universal setup in which higher-order operators suppressed by a large energy scale trigger this instability. This phenomenon can prematurely end inflation, thereby leading to important observational consequences and sometimes excluding models that would otherwise perfectly fit the data...
September 30, 2016: Physical Review Letters
Grigor Aslanyan, Layne C Price, Jenni Adams, Torsten Bringmann, Hamish A Clark, Richard Easther, Geraint F Lewis, Pat Scott
Cosmological inflation generates primordial density perturbations on all scales, including those far too small to contribute to the cosmic microwave background. At these scales, isolated ultracompact minihalos of dark matter can form well before standard structure formation, if the perturbations have sufficient amplitude. Minihalos affect pulsar timing data and are potentially bright sources of gamma rays. The resulting constraints significantly extend the observable window of inflation in the presence of cold dark matter, coupling two of the key problems in modern cosmology...
September 30, 2016: Physical Review Letters
Ue-Li Pen, Neil Turok
We point out a surprising consequence of the usually assumed initial conditions for cosmological perturbations. Namely, a spectrum of Gaussian, linear, adiabatic, scalar, growing mode perturbations not only creates acoustic oscillations of the kind observed on very large scales today, it also leads to the production of shocks in the radiation fluid of the very early Universe. Shocks cause departures from local thermal equilibrium as well as create vorticity and gravitational waves. For a scale-invariant spectrum and standard model physics, shocks form for temperatures 1  GeV<T<10^{7}  GeV...
September 23, 2016: Physical Review Letters
Daniela Saadeh, Stephen M Feeney, Andrew Pontzen, Hiranya V Peiris, Jason D McEwen
A fundamental assumption in the standard model of cosmology is that the Universe is isotropic on large scales. Breaking this assumption leads to a set of solutions to Einstein's field equations, known as Bianchi cosmologies, only a subset of which have ever been tested against data. For the first time, we consider all degrees of freedom in these solutions to conduct a general test of isotropy using cosmic microwave background temperature and polarization data from Planck. For the vector mode (associated with vorticity), we obtain a limit on the anisotropic expansion of (σ_{V}/H)_{0}<4...
September 23, 2016: Physical Review Letters
Anna Ijjas, Paul J Steinhardt
One of the fundamental questions of theoretical cosmology is whether the Universe can undergo a nonsingular bounce, i.e., smoothly transit from a period of contraction to a period of expansion through violation of the null energy condition (NEC) at energies well below the Planck scale and at finite values of the scale factor such that the entire evolution remains classical. A common claim has been that a nonsingular bounce either leads to ghost or gradient instabilities or a cosmological singularity. In this Letter, we consider a well-motivated class of theories based on the cubic Galileon action and present a procedure for explicitly constructing examples of a nonsingular cosmological bounce without encountering any pathologies and maintaining a subluminal sound speed for comoving curvature modes throughout the NEC violating phase...
September 16, 2016: Physical Review Letters
Emanuele Berti, Alberto Sesana, Enrico Barausse, Vitor Cardoso, Krzysztof Belczynski
We estimate the potential of present and future interferometric gravitational-wave detectors to test the Kerr nature of black holes through "gravitational spectroscopy," i.e., the measurement of multiple quasinormal mode frequencies from the remnant of a black hole merger. Using population synthesis models of the formation and evolution of stellar-mass black hole binaries, we find that Voyager-class interferometers will be necessary to perform these tests. Gravitational spectroscopy in the local Universe may become routine with the Einstein Telescope, but a 40-km facility like Cosmic Explorer is necessary to go beyond z∼3...
September 2, 2016: Physical Review Letters
Nico Hamaus, Alice Pisani, P M Sutter, Guilhem Lavaux, Stéphanie Escoffier, Benjamin D Wandelt, Jochen Weller
The Universe is mostly composed of large and relatively empty domains known as cosmic voids, whereas its matter content is predominantly distributed along their boundaries. The remaining material inside them, either dark or luminous matter, is attracted to these boundaries and causes voids to expand faster and to grow emptier over time. Using the distribution of galaxies centered on voids identified in the Sloan Digital Sky Survey and adopting minimal assumptions on the statistical motion of these galaxies, we constrain the average matter content Ω_{m}=0...
August 26, 2016: Physical Review Letters
A Trenkwalder, G Spagnolli, G Semeghini, S Coop, M Landini, P Castilho, L Pezzè, G Modugno, M Inguscio, A Smerzi, M Fattori
Symmetry-breaking quantum phase transitions play a key role in several condensed matter, cosmology and nuclear physics theoretical models1-3. Its observation in real systems is often hampered by finite temperatures and limited control of the system parameters. In this work we report for the first time the experimental observation of the full quantum phase diagram across a transition where the spatial parity symmetry is broken. Our system is made of an ultra-cold gas with tunable attractive interactions trapped in a spatially symmetric double-well potential...
September 2016: Nature Physics
Bron Taylor, Gretel Van Wieren, Bernard Daley Zaleha
Lynn White Jr.'s "The Historical Roots of Our Ecologic Crisis," which was published in Science in 1967, has played a critical role in precipitating interdisciplinary environmental studies. Although White advances a multifaceted argument, most respondents focus on his claim that the Judeo-Christian tradition, especially Christianity, has promoted anthropocentric attitudes and environmentally destructive behaviors. Decades later, some scholars argue contrarily that Christianity in particular and the world's predominant religions in general are becoming more environmentally friendly, known as the greening-of-religion hypothesis...
October 2016: Conservation Biology: the Journal of the Society for Conservation Biology
Yi-Fu Cai, Salvatore Capozziello, Mariafelicia De Laurentis, Emmanuel N Saridakis
Over recent decades, the role of torsion in gravity has been extensively investigated along the main direction of bringing gravity closer to its gauge formulation and incorporating spin in a geometric description. Here we review various torsional constructions, from teleparallel, to Einstein-Cartan, and metric-affine gauge theories, resulting in extending torsional gravity in the paradigm of f (T) gravity, where f (T) is an arbitrary function of the torsion scalar. Based on this theory, we further review the corresponding cosmological and astrophysical applications...
October 2016: Reports on Progress in Physics
Luca Alberto Rizzo, David F Mota, Patrick Valageas
We present exact kinematic consistency relations for cosmological structures that do not vanish at equal times and can thus be measured in surveys. These rely on cross correlations between the density and velocity, or momentum, fields. Indeed, the uniform transport of small-scale structures by long-wavelength modes, which cannot be detected at equal times by looking at density correlations only, gives rise to a shift in the amplitude of the velocity field that could be measured. These consistency relations only rely on the weak equivalence principle and Gaussian initial conditions...
August 19, 2016: Physical Review Letters
Paul Richard Kauffman
There are many historical examples of people who heard voices or saw visions but were not classified as having a mental illness and who were supported by a religious community. The article offers a perspective for effective psychosocial supports for schizophrenia. The author analyzes data on 95 people who experienced verifiable persistent non-drug-assisted hallucinations in Europe, North America, and Australasia and discusses the life outcomes of 39 subjects. They include founders of religions, dysfunctional monarchs, persons with cosmological beliefs, and mental health workers...
September 2016: Journal of Nervous and Mental Disease
Joseph A Tainter
The study of cultural complexity is entwined with ancestors myths from contemporary cosmology. Gowdy & Krall expose this mythology by arguing that complexity emerged from economic changes following cultivation. There is more, however, to the development of cultural complexity. Complexity can emerge from abundant energy or from addressing societal problems, which compels still further energy production.
January 2016: Behavioral and Brain Sciences
J Colin Hill, Simone Ferraro, Nick Battaglia, Jia Liu, David N Spergel
The kinematic Sunyaev-Zel'dovich (KSZ) effect-the Doppler boosting of cosmic microwave background (CMB) photons due to Compton scattering off free electrons with nonzero bulk velocity-probes the abundance and the distribution of baryons in the Universe. All KSZ measurements to date have explicitly required spectroscopic redshifts. Here, we implement a novel estimator for the KSZ-large-scale structure cross-correlation based on projected fields: it does not require redshift estimates for individual objects, allowing KSZ measurements from large-scale imaging surveys...
July 29, 2016: Physical Review Letters
B Wang, E Abdalla, F Atrio-Barandela, D Pavón
Models where dark matter and dark energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector...
September 2016: Reports on Progress in Physics
Dennis Sölch
The case of William Morton Wheeler and Alfred North Whitehead represents a striking example of how biologists and philosophers engaged in a common enterprise in the early twentieth century. Both challenge the notion that the living world is composed of distinct organisms. Based on his studies of the behavior of social insects, Wheeler developed a concept of superorganisms that paved the way for a theory of emergent evolution. This paper argues that Whitehead, whose relation to academic biology has been largely ignored, drew on Wheeler's findings and integrated them into a universal philosophical cosmology...
July 2016: Journal of the History of Ideas
Steffen Gielen, Neil Turok
We study quantum cosmology with conformal matter comprising a perfect radiation fluid and a number of conformally coupled scalar fields. Focusing initially on the collective coordinates (minisuperspace) associated with homogeneous, isotropic backgrounds, we are able to perform the quantum gravity path integral exactly. The evolution describes a "perfect bounce", in which the Universe passes smoothly through the singularity. We extend the analysis to spatially flat, anisotropic universes, treated exactly, and to generic inhomogeneous, anisotropic perturbations treated at linear and nonlinear order...
July 8, 2016: Physical Review Letters
J Jeknić-Dugić, M Arsenijević, M Dugić
Recently we pointed out the so-called local time scheme as a novel approach to quantum foundations that solves the preferred pointer-basis problem. In this paper, we introduce and analyse in depth a rather non-standard dynamical map that is imposed by the scheme. On the one hand, the map does not allow for introducing a properly defined generator of the evolution nor does it represent a quantum channel. On the other hand, the map is linear, positive, trace preserving and unital as well as completely positive, but is not divisible and therefore non-Markovian...
June 2016: Proceedings. Mathematical, Physical, and Engineering Sciences
Toomas Gross
"Air (aire, also aigre) in the body" is a frequent explanation of illness according to the traditional medical beliefs in Mexico. Anthropologists have generally scrutinized aire in the context of other common folk illnesses treated by traditional healers (curanderas). However, drawing on my research in the communities of Northern Oaxaca I suggest that aire occupies a more distinct position in the folk medical cosmology than it has usually been credited with. This distinction rests on the notion's exceptional ambivalence and openness to multiple interpretations...
July 18, 2016: Culture, Medicine and Psychiatry
John T Giblin, James B Mertens, Glenn D Starkman
While the use of numerical general relativity for modeling astrophysical phenomena and compact objects is commonplace, the application to cosmological scenarios is only just beginning. Here, we examine the expansion of a spacetime using the Baumgarte-Shapiro-Shibata-Nakamura formalism of numerical relativity in synchronous gauge. This work represents the first numerical cosmological study that is fully relativistic, nonlinear, and without symmetry. The universe that emerges exhibits an average Friedmann-Lemaître-Robertson-Walker (FLRW) behavior; however, this universe also exhibits locally inhomogeneous expansion beyond that expected in linear perturbation theory around a FLRW background...
June 24, 2016: Physical Review Letters
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