Neutron limit on the strongly-coupled chameleon field

Abstract

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 β ranging from β < 4.7 × 10 6 for a Ratra-Peebles index of n = 1 in the nonlinear scalar field potential to β < 2.4 × 10 7 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.

Noise refocusing in a five-blade neutron interferometer

“…Matter wave interferometry is a powerful and extremely sensitive tool to probe effects ranging from material properties to foundational physics [1][2][3][4] . Although high sensitivity and accuracy are achieved due to matter waves' small deBroglie wavelength and statistical inference, these massive particles couple to external degrees of freedom (DOF) leading to loss of coherence.…”

Cold and Ultra-cold Neutrons as Probes of New Physics

“…Lemmel et al [162] recently presented phase shift measurements for neutron matter waves in vacuum and in low pressure helium using a method originally developed for neutron scattering lengths measurements. Li et al [163] reported an upper bound on the neutron-chameleon 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.…”

Three Phase-Grating Moiré Neutron Interferometer for Large Interferometer Area Applications

“…Amplitude division from Bragg diffraction off of crystal planes was later used to make perfect crystal NIs with Mach-Zehnder (MZ) path separations of several centimeters [4]. This relatively large path separation along with the macroscopic size of the interferometer contributed to its success in exploring the nature of the neutron and its interactions [5][6][7][8][9][10]. However, perfect crystal NIs possess a very narrow wavelength acceptance, are difficult to fabricate, and operate only under stringent forms of vibration isolation and beam collimation [11][12][13][14][15].…”