Constraining D-foam via the 21-cm line

Abstract

We have suggested earlier that D-particles, which are stringy space-time defects predicted in braneinspired models of the Universe, might constitute a component of dark matter, and that they might contribute to the masses of singlet fermions that could provide another component. Interactions of the quantum-fluctuating D-particles with matter induce vector forces that are mediated by a massless effective U(1) gauge field, the "D-photon", which is distinct from the ordinary photon and has different properties from dark photons. We discuss the form of interactions of D-matter with conventional matter induced by D-photon exchange and calculate their strength, which depends on the density of D-particles. Observations of the hydrogen 21 cm line at redshifts 15 can constrain these interactions and the density of D-matter in the early Universe. I. INTRODUCTIONThe nature of dark matter (DM) is one of the biggest mysteries in cosmology and particle physics. It is commonly thought to be composed of one or more unknown species of particles, with popular candidates ranging from ultralight bosons such as axions, through sterile neutrinos and TeV-scale to supermassive metastable particles [1]. Alternatively, the possibility that dark matter might be composed of black holes has gained in interest following the recent observations of gravitational waves emitted by mergers of black holes [2]. Another current of opinion is that dark matter might be due to some unexpected gravitational phenomenon [3]. We have been pursuing a scenario for dark matter that is complementary to these approaches, though with some aspects in common.Our starting-point is an attempt to model quantum fluctuations in space-time -"space-time foam" [4] -using elements derived from string theory [5], in which the Universe may be modelled as a three-brane world moving in a higher-dimensional bulk space [6][7][8][9][10][11]. Generic string models predict the appearance in this bulk space of point-like space-time defects called D-particles [12], such as D0-branes in Type IIA strings and D3-branes wrapped around appropriate three-cycles in Type IIB strings. As the three-brane world and the D-particles move in the bulk, they may encounter each other, in which case an observer on the three-brane perceives the D-particle defects as flashing on and off, giving the 3+1-dimensional space-time a foamy structure. In such a scenario, ordinary matter and radiation are represented by open strings with their ends attached on the three-brane.Some of the D-particles may be trapped on the three-brane, in which case they would act as dark matter [13,14]. However, depending on the dynamics of the bulk and the three-brane, the density of D-particles on the three-brane may evolve differently from the conventional dust-like dilution of matter density as the Universe expands. The D-particles interact with conventional matter particles via the capture and subsequent re-emission of open strings, accompanied by recoil of the D-particle [15]. Such interactions with D-particles could contrib...

Testing Lorentz Invariance Violation at the Pierre Auger Observatory

“…Potential LIV signatures are expected from several different astrophysical contexts. Previous studies have searched for LIV signals using distinct results, such as the time of flight of photons generated in gamma-ray bursts [2,3,4], modulations of the energy spectrum in TeV gamma-rays [5,6,7] and ultra-high energy cosmic rays (UHECR) [8,9], and upper limits on the flux of EeV photons [10,11]. No LIV signal has yet been found [1] and, thus, restrictive limits on the violation have been set [12].…”