Hawking radiation from the quantum Lemaitre-Tolman-Bondi model

In an earlier paper, we obtained exact solutions of the Wheeler-DeWitt equation for the Lemaitre-Tolman-Bondi (LTB) model of gravitational collapse, employing a lattice regularization. In this paper, we derive Hawking radiation in non-marginally bound models from our exact solutions. We show that a non-vanishing energy function does not spoil the (approximate) Planck spectrum near the horizon. We can also reliably compute corrections to the Bogoliubov coefficient because our solutions are exact. The corrections are obtained by going beyond the near horizon region and are shown to introduce additional greybody factors, which modify the black body spectrum of radiation from the black hole.Comment: 14 page

No black hole information puzzle in a relational universe

The introduction of a relational time in quantum gravity naturally implies that pure quantum states evolve into mixed quantum states. We show, using a recently proposed concrete implementation, that the rate at which pure states naturally evolve into mixed ones is faster than that due to collapsing into a black hole that later evaporates. This is rather remarkable since the fundamental mechanism for decoherence is usually very weak. Therefore the ``black hole information puzzle'' is rendered de-facto unobservable.Comment: 4 pages, no figures, revte

Signatures of magnetic activity in the seismic data of solar-type stars observed by Kepler

In the Sun, the frequencies of the acoustic modes are observed to vary in phase with the magnetic activity level. These frequency variations are expected to be common in solar-type stars and contain information about the activity-related changes that take place in their interiors. The unprecedented duration of Kepler photometric time-series provides a unique opportunity to detect and characterize stellar magnetic cycles through asteroseismology. In this work, we analyze a sample of 87 solar-type stars, measuring their temporal frequency shifts over segments of length 90 days. For each segment, the individual frequencies are obtained through a Bayesian peak-bagging tool. The mean frequency shifts are then computed and compared with: 1) those obtained from a cross-correlation method; 2) the variation in the mode heights; 3) a photometric activity proxy; and 4) the characteristic timescale of the granulation. For each star and 90-d sub-series, we provide mean frequency shifts, mode heights, and characteristic timescales of the granulation. Interestingly, more than 60% of the stars show evidence for (quasi-)periodic variations in the frequency shifts. In the majority of the cases, these variations are accompanied by variations in other activity proxies. About 20% of the stars show mode frequencies and heights varying approximately in phase, in opposition to what is observed for the Sun.Comment: Accepted for publication in ApJS, 19(+86) pages, 11(+89) figures, 2(+87) table

Seismic signatures of magnetic activity in solar-type stars observed by Kepler

The properties of the acoustic modes are sensitive to magnetic activity. The unprecedented long-term Kepler photometry, thus, allows stellar magnetic cycles to be studied through asteroseismology. We search for signatures of magnetic cycles in the seismic data of Kepler solar-type stars. We find evidence for periodic variations in the acoustic properties of about half of the 87 analysed stars. In these proceedings, we highlight the results obtained for two such stars, namely KIC 8006161 and KIC 5184732.Comment: 4 pages, 1 figure, to appear in the Proceedings of the IAUS34

Topology, Decoherence, and Semiclassical Gravity

We address the issue of recovering the time-dependent Schr\"{o}dinger equation from quantum gravity in a natural way. To reach this aim it is necessary to understand the nonoccurrence of certain superpositions in quantum gravity. We explore various possible explanations and their relation. These are the delocalisation of interference terms through interaction with irrelevant degrees of freedom (decoherence), gravitational anomalies, and the possibility of $\theta$ states. The discussion is carried out in both the geometrodynamical and connection representation of canonical quantum gravity.Comment: 18 pages, ZU-TH 3/93, to appear in Phys. Rev.

Scaling up business plans in Tajikistan: a qualitative study of the history, barriers, facilitators and lessons learnt

BACKGROUND: To improve health planning at primary health care (PHC) level, Business Plans were introduced in Tajikistan by the Enhancing Primary Health Care (EPHC) Services Project. OBJECTIVE: To describe the history and process of implementation of Business Plans and to identify barriers, facilitators and lessons learnt from scaling up Business Plans. METHODS: Set in a qualitative research design, we conducted a desk review of project and official documents and seventeen semi-structured interviews with key stakeholders at national and sub-national levels between May and July 2020. We used an interview guide informed by the ExpandNet/WHO framework and analyzed the data following a content analysis approach facilitated by MAXQDA. RESULTS: With the participation of various user organizations and resource teams and through a variety of strategic scale-up choices, Business Plans have been scaled up from a vertical pilot project to institutionalized health management tools covering 45% of Tajikistan's PHC facilities. The most prominent facilitators for scaling up Business Plans were the institutionalization and integration of the tool into the Tajik health system, the close collaboration with Community Health Teams (CHTs), the high acceptance of the tool among the users, the advocacy through champions and policy-makers and the large dissemination network. The most outstanding barriers to scaling up Business Plans were insufficient financial or human resources, general weaknesses in health governance, the lack of a strategic scale-up plan and strategic decisions, the lack of motivation or overall vision to implement Business Plans at a large scale and difficulties in donor coordination. CONCLUSION: To ensure the continuity of scaling up Business Plans, developing a scale-up strategy, strengthening cross-sectoral collaboration and participation during scaling up, and capacitating the user organizations of Business Plans are important next steps to ensure the sustainability and effectiveness of Business Plans in the future

Solitonic lattice and Yukawa forces in the rare earth orthoferrite TbFeO3

The control of domains in ferroic devices lies at the heart of their potential for technological applications. Multiferroic materials offer another level of complexity as domains can be either or both of a ferroelectric and magnetic nature. Here we report the discovery of a novel magnetic state in the orthoferrite TbFeO3 using neutron diffraction under an applied magnetic field. This state has a very long incommensurate period ranging from 340 Angstrom at 3K to 2700 Angstrom at the lowest temperatures and exhibits an anomalously large number of higher-order harmonics, allowing us to identify it with the periodic array of sharp domain walls of Tb spins separated by many lattice constants. The Tb domain walls interact by exchanging spin waves propagating through the Fe magnetic sublattice. The resulting Yukawa-like force, familiar from particle physics, has a finite range that determines the period of the incommensurate state.Comment: 11 pages 14 figure

Noncommutative Geometry and Cosmology

We study some consequences of noncommutativity to homogeneous cosmologies by introducing a deformation of the commutation relation between the minisuperspace variables. The investigation is carried out for the Kantowski-Sachs model by means of a comparative study of the universe evolution in four different scenarios: the classical commutative, classical noncommutative, quantum commutative, and quantum noncommutative. The comparison is rendered transparent by the use of the Bohmian formalism of quantum trajectories. As a result of our analysis, we found that noncommutativity can modify significantly the universe evolution, but cannot alter its singular behavior in the classical context. Quantum effects, on the other hand, can originate non-singular periodic universes in both commutative and noncommutative cases. The quantum noncommutative model is shown to present interesting properties, as the capability to give rise to non-trivial dynamics in situations where its commutative counterpart is necessarily static.Comment: 22 pages, 5 figures, substantial changes in the presentation, results are the same, to appear in Physical Review

Noncommutative Conformally Coupled Scalar Field Cosmology and its Commutative Counterpart

We study the implications of a noncommutative geometry of the minisuperspace variables for the FRW universe with a conformally coupled scalar field. The investigation is carried out by means of a comparative study of the universe evolution in four different scenarios: classical commutative, classical noncommutative, quantum commutative, and quantum noncommutative, the last two employing the Bohmian formalism of quantum trajectories. The role of noncommutativity is discussed by drawing a parallel between its realizations in two possible frameworks for physical interpretation: the NC-frame, where it is manifest in the universe degrees of freedom, and in the C-frame, where it is manifest through theta-dependent terms in the Hamiltonian. As a result of our comparative analysis, we find that noncommutative geometry can remove singularities in the classical context for sufficiently large values of theta. Moreover, under special conditions, the classical noncommutative model can admit bouncing solutions characteristic of the commutative quantum FRW universe. In the quantum context, we find non-singular universe solutions containing bounces or being periodic in the quantum commutative model. When noncommutativity effects are turned on in the quantum scenario, they can introduce significant modifications that change the singular behavior of the universe solutions or that render them dynamical whenever they are static in the commutative case. The effects of noncommutativity are completely specified only when one of the frames for its realization is adopted as the physical one. Non-singular solutions in the NC-frame can be mapped into singular ones in the C-frame.Comment: explanations added, references include