Couplings between holographic dark energy and dark matter

We consider the interaction between dark matter and dark energy in the framework of holographic dark energy, and propose a natural and physically plausible form of interaction, in which the interacting term is proportional to the product of the powers of the dark matter and dark energy densities. We investigate the cosmic evolution in such models. The impact of the coupling on the dark matter and dark energy components may be asymmetric. While the dark energy decouples from the dark matter at late time, just as other components of the cosmic fluid become decoupled as the universe expands, interestingly, the dark matter may actually become coupled to the dark energy at late time. We shall call such a phenomenon incoupling. We use the latest type Ia supernovae data from the SCP team, baryon acoustics oscillation data from SDSS and 2dF surveys, and the position of the first peak of the CMB angular power spectrum to constrain the model. We find that the interaction term which is proportional to the first power product of the dark energy and dark matter densities gives an excellent fit to the current data.     

Effective theory for dark matter and a new force in the dark matter sector

An effective theory for dark matter has recently been proposed. The key assumption is that the dark matter particle which is a Dirac fermion is protected from decaying by a global U(1) symmetry. We point out that quantum gravity effects will violate this symmetry and that the dark matter candidate thus decays very fast. In order to solve that problem, we propose to consider a local gauge symmetry which implies a new force in the dark matter sector. It is likely that this new local U(1) symmetry will need to be spontaneously broken leading for a range of the parameters of the model to a Sommerfeld enhancement of the annihilation cross sections which is useful to explain the Pamela and ATIC results using a weakly interacting massive particle with a mass in the TeV range.     

Neutrino sector impacts SUSY dark matter

Motivated by the fact that neutrinos are massive, we study the effect of neutrino Yukawa couplings on neutralino dark matter observables within the framework of a supersymmetric seesaw. We find that neutrino couplings significantly affect the neutralino relic density in regions of parameter space where soft SUSY-breaking slepton masses and/or trilinear couplings are large. Depending on the size of the couplings, the neutralino relic density spans over an order of magnitude in the A-funnel, focus point and stop-coannihilation regions of mSUGRA. We also show that dark matter detection rates can be modified by up to several orders of magnitude.     

Perfect fluid dark matter

Taking the flat rotation curve as input and treating the matter content in the galactic halo region as perfect fluid we obtain a space–time metric at the galactic halo region in the framework of general relativity. We find that the resultant space–time metric is a non-relativistic dark matter induced space–time embedded in a static Friedmann–Lemaître–Robertson–Walker universe i.e. the flat rotation curve not only leads to the existence of dark matter but also suggests about the background geometry of the universe. Within its range of validity the flat rotation curve and the demand that the dark matter to be non-exotic together indicate for a (nearly) flat universe as favored by the modern cosmological observations. We obtain the expressions for energy density and pressure of dark matter there and consequently the equation of state of dark matter. Various other aspects of the solutions are also analyzed.     

Asymmetric dark matter from hidden sector baryogenesis

We consider the production of asymmetric dark matter during hidden sector baryogenesis. We consider a particular supersymmetric model where the dark matter candidate has a number density approximately equal to the baryon number density, with a mass of the same scale as the b, c and τ. Both baryon asymmetry and dark matter are created at the same time in this model. We describe collider and direct detection signatures of this model.     

Collider search of light dark matter model with dark sector decay

We explore the possibility that the dark matter relic density is not produced by a thermal mechanism directly, but by the decay of other heavier dark-sector particles which themselves can be produced by the thermal freeze-out mechanism. Using a concrete model with light dark matter from dark sector decay, we study the collider signature of the dark sector particles associated with Higgs production processes. We find that future lepton colliders could be a better place to probe the signature of this kind of light dark matter model than hadron colliders such as LHC. Also, we find that a Higgs factory with center-of-mass energy 250 GeV has a better potential to resolve the signature of this kind of light dark matter model than a Higgs factory with center-of-mass energy 350 GeV.     

Self-gravitating fluid systems and galactic dark matter

We study gravitational collapse with anisotropic pressures, whose end stage can mimic space–times that are seeded by galactic dark matter. To this end, we identify a class of space–times (with conical defects) that can arise out of such a collapse process, and admit stable circular orbits at all radial distances. These have a naked singularity at the origin. An example of such a space–time is seen to be the Bertrand space–time discovered by Perlick, that admits closed, stable orbits at all radii. Using relativistic two-fluid models, we show that our galactic space–times might indicate exotic matter, i.e one of the component fluids may have negative pressure for a certain asymptotic fall off of the associated mass density, in the Newtonian limit. We complement this analysis by studying some simple examples of Newtonian two-fluid systems, and compare this with the Newtonian limit of the relativistic systems considered.     

Bardeen black hole surrounded by perfect fluid dark matter

We derive an exact solution for a spherically symmetric Bardeen black hole surrounded by perfect fluid dark matter (PFDM). By treating the magnetic charge g and dark matter parameter \begin{document}$\alpha$\end{document} as thermodynamic variables, we find that the first law of thermodynamics and the corresponding Smarr formula are satisfied. The thermodynamic stability of the black hole is also studied. The results show that there exists a critical radius \begin{document}$r_{+}^{C}$\end{document} where the heat capacity diverges, suggesting that the black hole is thermodynamically stable in the range \begin{document}$0<r_{+}<r_{+}^{C}$\end{document} . In addition, the critical radius \begin{document}$r_{+}^{C}$\end{document} increases with the magnetic charge g and decreases with the dark matter parameter \begin{document}$\alpha$\end{document} . Applying the Newman-Janis algorithm, we generalize the spherically symmetric solution to the corresponding rotating black hole. With the metric at hand, the horizons and ergospheres are studied. It turns out that for a fixed dark matter parameter \begin{document}$\alpha$\end{document} , in a certain range, with the increase of the rotation parameter a and magnetic charge g, the Cauchy horizon radius increases while the event horizon radius decreases. Finally, we investigate the energy extraction by the Penrose process in a rotating Bardeen black hole surrounded by PFDM.     

Entanglement in holographic dark energy models

We study a process of equilibration of holographic dark energy (HDE) with the cosmic horizon around the dark-energy dominated epoch. This process is characterized by a huge amount of information conveyed across the horizon, filling thereby a large gap in entropy between the system on the brink of experiencing a sudden collapse to a black hole and the black hole itself. At the same time, even in the absence of interaction between dark matter and dark energy, such a process marks a strong jump in the entanglement entropy, measuring the quantum-mechanical correlations between the horizon and its interior. Although the effective quantum field theory (QFT) with a peculiar relationship between the UV and IR cutoffs, a framework underlying all HDE models, may formally account for such a huge shift in the number of distinct quantum states, we show that the scope of such a framework becomes tremendously restricted, devoid virtually any application in other cosmological epochs or particle-physics phenomena. The problem of negative entropies for the non-phantom stuff is also discussed.     

Theoretical aspects of holographic dark energy

We review the theoretical aspects of holographic dark energy(HDE) in this paper.Making use of the holographic principle(HP) and the dimensional analysis, we derive the core formula of the original HDE(OHDE) model, in which the future event horizon is chosen as the characteristic length scale. Then, we describe the basic properties and the corresponding theoretical studies of the OHDE model, as well as the effect of adding dark sector interaction in the OHDE model. Moreover, we introduce all four...     

Restoring holographic dark energy in brane cosmology

We present a generalized version of holographic dark energy arguing that it must be considered in the maximally subspace of a cosmological model. In the context of brane cosmology it leads to a bulk holographic dark energy which transfers its holographic nature to the effective 4D dark energy. As an application we use a single-brane model and we show that in the low energy limit the behavior of the effective holographic dark energy coincides with that predicted by conventional 4D calculations. However, a finite bulk can lead to radically different results.     

Explaining the W boson mass anomaly and dark matter with a U(1) dark sector

The W boson mass recently reported by the CDF collaboration shows a deviation from the standard model prediction with an excess at the \begin{document}$ 7\sigma $\end{document} level. We investigate two simple extensions of the standard model with an extra \begin{document}$ U(1) $\end{document} dark sector. One is the \begin{document}$ U(1)_x $\end{document} extension, where the \begin{document}$ U(1)_x $\end{document} gauge field mixes with the standard model through gauge kinetic terms. The other is a general \begin{document}$ U(1)_{\mathbf{A} Y+\mathbf{B} q} $\end{document} extension of the standard model. Fitting various experimental constraints, we find that the \begin{document}$ U(1)_x $\end{document}extension with only kinetic mixing can enhance the W boson mass by 10 MeV at most. The\begin{document}$ U(1)_{\mathbf{A} Y+\mathbf{B} q} $\end{document}extension can easily generate a 77 MeV enhancement of the W boson mass and also offer a viable dark matter candidate with a mass ranging from several hundred GeV to TeV, which may be detected by future dark matter direct detection experiments with improved sensitivities.     

Spin in the dark matter problem

Weakly interacting massive particles (WIMPs) are among the main candidates for the relic dark matter (DM). The idea of direct DM detection relies on elastic spin-dependent (SD) and spin-independent (SI) interaction of WIMPs with target nuclei. In this review, formulas for the DM event rate calculations are collected. The importance of the SD WIMP-nucleus interaction for reliable DM detection is argued and the spin nuclear structure functions relevant to DM search are discussed. The effective low-energy minimal supersymmetric standard model (MSSM) is used for calculation of the DM cross sections, provided the lightest neutralino is the WIMP. It is shown that the absolute lower bound for the rate of direct DM detection is due to the SD WIMP-nucleon interaction and a new-generation experiment aimed at detecting DM with sensitivity higher than 10⁻⁵ event/day/kg should have a non-zero-spin target to avoid missing of the DM signal. The mixed spin-scalar couplings approach is argued. Prospects of DM experiments with high-spin Ge-73 are discussed in the mixed coupling scheme. The DAMA experiment has claimed observation of WIMPs due to annual signal modulation. Some important consequences of the DAMA claim for the other DM searches as well as for collider physics are considered. The text was submitted by the author in English.