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The current standard model of cosmology, ΛCDM, requires dark matter to make up around 25% of the total energy budget of the Universe. Yet, quite puzzlingly, there appears to be no candidate particle in the current Standard Model of particle physics. Assuming the validity of the cold dark matter (CDM) paradigm, dark matter has evaded detection thus far either because it is intrinsically a weakly interacting substance or because its interactions are suppressed by its high constituent mass and low number density. Most approaches to explain dark matter to date assume the former and therefore require beyond-the-Standard-Model particles that have yet to be observed directly or indirectly. Given the dearth of evidence for this class of candidates it is timely to consider the latter possibility, which allows for candidates that may or may not arise from the Standard Model. In this work we extend a recent study of this general class of so-called macro dark matter--candidates with characteristic masses of grams and geometric cross sections of cm². We consider new bounds that can be set using existing data from the resonant bar gravitational wave detectors NAUTILUS and EXPLORER. [ABSTRACT FROM AUTHOR]

We study a model of interacting dark matter and dark energy, in which the two components are coupled. We calculate the predictions for the 21-cm intensity mapping power spectra, and forecast the detectability with future single-dish intensity mapping surveys (BINGO, FAST and SKA-I). Since dark energy is turned on at z∼1, which falls into the sensitivity range of these radio surveys, the HI intensity mapping technique is an efficient tool to constrain the interaction. By comparing with current constraints on dark sector interactions, we find that future radio surveys will produce tight and reliable constraints on the coupling parameters. [ABSTRACT FROM AUTHOR]

A violation of the reciprocity relation, which induces a violation of the distance-duality relation, reflects itself in a change in the normalization of the cosmic microwave spectrum in such a way that its spectrum is grey. We show that existing observational constraints imply that the reciprocity relation cannot be violated by more than 0.01% between decoupling and today. We compare this effect to other sources of violation of the distance-duality relations which induce spectral distortion of the cosmic microwave background spectrum. [ABSTRACT FROM AUTHOR]

The dispersion measure--redshift relation of fast radio bursts (FRBs), DM(z), has been proposed as a potential new probe of the cosmos, complementary to existing techniques. In practice, however, the effectiveness of this approach depends on a number of factors, including (but not limited to) the intrinsic scatter in the data caused by intervening matter inhomogeneities. Here, we simulate a number of catalogues of mock FRB observations, and use Markov Chain Monte Carlo techniques to forecast constraints, and assess which parameters will likely be best constrained. In all cases, we find that any potential improvement in cosmological constraints are limited by the current uncertainty on the diffuse gas fraction, fd(z). Instead, we find that the precision of current cosmological constraints allows one to constrain fd(z) and possibly its redshift evolution. Combining Cosmic Microwave Background + Baryon Acoustic Oscillations + Supernovae + H0 constraints with just 100 FRBs (with redshifts), we find a typical constraint on the mean diffuse gas fraction of a few percent. A detection of this nature would alleviate the "missing baryon problem," and therefore highlights the value of localization and spectroscopic follow-up of future FRB detections. [ABSTRACT FROM AUTHOR]

We investigate the cosmological solutions coming from the double field theory equations of motion after coupling a matter source to them. Assuming constant dilaton and imposing the section condition with respect to the regular coordinates leads to a universe dominated by momentum modes while imposing the section condition with respect to the dual coordinates naturally leads to a universe dominated by momentum modes. We show that both regimes have asymptotic behaviors related by T duality. This hints towards defining a duality between the clocks considered in each regime and interpreting winding modes as being radiation from the point of view of a Euclidean time. [ABSTRACT FROM AUTHOR]

Making use of the T-duality symmetry of superstring theory and of the double geometry from double field theory, we argue that cosmological singularities of a homogeneous and isotropic universe disappear. In fact, an apparent big bang singularity in Einstein gravity corresponds to a universe expanding to infinite size in the dual dimensions. [ABSTRACT FROM AUTHOR]

We generalize the action for point particle motion to a double field theory background. After deriving the general equations of motion for these particle geodesics, we specialize to the case of a cosmological background with vanishing antisymmetric tensor field. We then show that the geodesics can be extended to infinity in both time directions once we define the appropriate physical clock. Following this prescription, we also show the existence of a singularity-free cosmological solution. [ABSTRACT FROM AUTHOR]

At present, the best model for the evolution of the cosmos requires that dark matter make up approximately 25% of the energy content of the Universe. Most approaches to explain the microscopic nature of dark matter, to date, have assumed its composition to be of intrinsically weakly interacting particles; however, this need not be the case to have consistency with all extant observations. Given decades of inconclusive evidence to support any dark matter candidate, there is strong motivation to consider alternatives to the standard particle scenario. One such example is macro dark matter, a class of candidates (macros) that could interact strongly with the particles of the Standard Model, have large masses and physical sizes, and yet behave as dark matter. Macros that scatter completely inelastically could have altered the primordial production of the elements, and macro charge-dependent constraints have been obtained previously. Here we reconsider the phenomenology of inelastically interacting macros on the abundance of primordially produced 4He and revise previous constraints by also taking into account improved measurements of the primordial 4He abundance. The constraints derived here are limited in applicability to only leptophobic macros that have a surface potential V(RX) ≳ 0.5 MeV. However, an important conclusion from our analysis is that even neutral macros would likely affect the abundance of the light elements. Therefore, constraints on that scenario are possible and are currently an open question. [ABSTRACT FROM AUTHOR]