Gibbons-Hawking Effect in the Sonic de Sitter Space-Time of an Expanding Bose-Einstein-Condensed Gas

We propose an experimental scheme to observe the Gibbons-Hawking effect in the acoustic analog of a 1+1-dimensional de Sitter universe, produced in an expanding, cigar-shaped Bose-Einstein condensate. It is shown that a two-level system created at the center of the trap, an atomic quantum dot interacting with phonons, observes a thermal Bose distribution at the de Sitter temperature.Comment: 4 pages, 2 figures, RevTex4; as publishe

The fate of the zero mode of the five-dimensional kink in the presence of gravity

We investigate what becomes of the translational zero-mode of a five-dimensional domain wall in the presence of gravity, studying the scalar perturbations of a thick gravitating domain wall with AdS asymptotics and a well-defined zero-gravity limit. Our analysis reveals the presence of a wide resonance which can be seen as a remnant of the translational zero-mode present in the domain wall in the absence of gravity and which ensures a continuous change of the physical quantities (such as e.g. static potential between sources) when the Planck mass is sent to infinity. Provided that the thickness of the wall is much smaller than the AdS radius of the space-time, the parameters of this resonance do not depend on details of the domain wall's structure, but solely on the geometry of the space-time.Comment: 29 pages, 4 figures; v2: 2 machine-generated typos in the introduction correcte

Dirac eigenvalues for a softcore Coulomb potential in d dimensions

A single fermion is bound by a softcore central Coulomb potential V(r) = -v/(r^q + b^q)^(1/q), v>0, b>0, q \ge 1, in d>1 spatial dimensions. Envelope theory is used to construct analytic lower bounds for the discrete Dirac energy spectrum. The results are compared to accurate eigenvalues obtained numerically.Comment: 8 pages 1 figur

Discovery of carotenoid red-shift in endolithic cyanobacteria from the Atacama Desert

Las respuestas bioquímicas de las cianobacterias que habitan en las rocas hacia el estrés ambiental nativo se observaron in vivo en uno de los entornos climáticos extremos más desafiantes de la Tierra. La colonización criptoendolítica de cianobacterias, dominada por Chroococcidiopsis sp., Se estudió en una ignimbrita en un área volcánica de gran altitud en el desierto de Atacama, Chile. El cambio en la composición de carotenoides (desplazamiento al rojo) dentro de un transecto a través de la comunidad microbiana dominante de cianobacterias (grosor promedio de ~ 1 mm) se reveló inequívocamente en su microhábitat endolítico natural. La cantidad de carotenoides desplazados al rojo, observada por primera vez en un ecosistema microbiano natural, depende de la profundidad y se incrementa a medida que aumenta la proximidad a la superficie de la roca, como lo demuestra la resonancia Raman y la resonancia puntual del perfil Raman. Se atribuye a un cambio dependiente de la luz en la conjugación de carotenoides, asociado con la estrategia de adaptación a la luz de las cianobacterias. Se propone una hipótesis para el posible papel de un mecanismo de extinción no fotoquímica (NPQ) mediado por la proteína carotenoide naranja (OCP) que influye en el comportamiento espectral observado. Simultáneamente, se obtuvo información sobre la distribución de scytonemin y phycobiliproteins. Scytonemin fue detectado en los agregados de cianobacterias superiores. Se registró un gradiente de intensidad de señal inverso de las ficobiliproteínas, que aumenta con las posiciones más profundas como respuesta del complejo de captura de luz de cianobacterias a condiciones de poca luz.The biochemical responses of rock-inhabiting cyanobacteria towards native environmental stresses were observed in vivo in one of the Earth’s most challenging extreme climatic environments. The cryptoendolithic cyanobacterial colonization, dominated by Chroococcidiopsis sp., was studied in an ignimbrite at a high altitude volcanic area in the Atacama Desert, Chile. Change in the carotenoid composition (red-shift) within a transect through the cyanobacteria dominant microbial community (average thickness ~1 mm) was unambiguously revealed in their natural endolithic microhabitat. The amount of red shifted carotenoid, observed for the first time in a natural microbial ecosystem, is depth dependent, and increased with increasing proximity to the rock surface, as proven by resonance Raman imaging and point resonance Raman profiling. It is attributed to a light-dependent change in carotenoid conjugation, associated with the light-adaptation strategy of cyanobacteria. A hypothesis is proposed for the possible role of an orange carotenoid protein (OCP) mediated non-photochemical quenching (NPQ) mechanism that influences the observed spectral behavior. Simultaneously, information about the distribution of scytonemin and phycobiliproteins was obtained. Scytonemin was detected in the uppermost cyanobacteria aggregates. A reverse signal intensity gradient of phycobiliproteins was registered, increasing with deeper positions as a response of the cyanobacterial light harvesting complex to low-light conditions.• Ministry of Education, Youth and Sports (República Checa) y el National Sustainability Program I (NPU I). Beca LO1415 • CzeCOS ProCES. Proyecto CZ.02.1.01/0.0/0.0/16_013/0001609 • Ministerio de Economía y Competitividad. Proyecto CGL2013-42509P, para Jaket Wierzchos, Octavio Artieda, Carmen Ascaso, María Cristina CaseropeerReviewe