Neutron limit on the strongly-coupled chameleon field.

The physical origin of the dark energy that causes the accelerated expansion rate of the Universe is one of the major open questions of cosmology. One set of theories postulates the existence of a self-interacting scalar field for dark energy coupling to matter. In the chameleon dark energy theory, this coupling induces a screening mechanism such that the field amplitude is nonzero in empty space but is greatly suppressed in regions of terrestrial matter density. However measurements performed under appropriate vacuum conditions can enable the chameleon field to appear in the apparatus, where it can be subjected to laboratory experiments. Here we report the most stringent upper bound on the free neutron-chameleon coupling in the strongly coupled limit of the chameleon theory using neutron interferometric techniques. Our experiment sought the chameleon field through the relative phase shift it would induce along one of the neutron paths inside a perfect crystal neutron interferometer. The amplitude of the chameleon field was actively modulated by varying the millibar pressures inside a dual-chamber aluminum cell. We report a 95% confidence level upper bound on the neutron-chameleon coupling ß ranging from ß < 4.7 × 106 for a Ratra-Peebles index of n = 1 in the nonlinear scalar field potential to ß < 2.4 × 107 for n = 6, one order of magnitude more sensitive than the most recent free neutron limit for intermediate n. Similar experiments can explore the full parameter range for chameleon dark energy in the foreseeable future.

Decoupling of a neutron interferometer from temperature gradients.

Neutron interferometry enables precision measurements that are typically operated within elaborate, multi-layered facilities which provide substantial shielding from environmental noise. These facilities are necessary to maintain the coherence requirements in a perfect crystal neutron interferometer which is extremely sensitive to local environmental conditions such as temperature gradients across the interferometer, external vibrations, and acoustic waves. The ease of operation and breadth of applications of perfect crystal neutron interferometry would greatly benefit from a mode of operation which relaxes these stringent isolation requirements. Here, the INDEX Collaboration and National Institute of Standards and Technology demonstrates the functionality of a neutron interferometer in vacuum and characterize the use of a compact vacuum chamber enclosure as a means to isolate the interferometer from spatial temperature gradients and time-dependent temperature fluctuations. The vacuum chamber is found to have no depreciable effect on the performance of the interferometer (contrast) while improving system stability, thereby showing that it is feasible to replace large temperature isolation and control systems with a compact vacuum enclosure for perfect crystal neutron interferometry.

[Aspects of aetiology of neuro-psychic disorders in male liquidators of Chernobyl nuclear power accident consequences].

The author considered aetiology of neuro-psychic disorders in liquidators of Chernobyl nuclear power accident consequences, demonstrated scientific value of studying the liquidators cohort, as they were protected from internal radiation factors and reside on radiation "pure" territories. External radiation doses in those liquidators vary from 16 cGy to 18.7 +/- 10.8 cGy, according to the author. Catamnesis enabled to doubt radiation aetiology of psychic organic syndrome revealed in 1991-1994 by clinical and instrumental studies among 53.6% of 213 male examinees. According to the author, prolonged over 1-2 months external radiation of low dose could not cause health deterioration in adult males. Diagnosed psychic organic syndrome and vascular encephalopathy in some cases could have alcohol aetiology. This conclusion is not extrapolated to the whole liquidators cohort.