Dark matter, dark energy, and alternate models: A review

https://doi.org/10.1016/j.asr.2017.03.043Get rights and content

Abstract

The nature of dark matter (DM) and dark energy (DE) which is supposed to constitute about 95% of the energy density of the universe is still a mystery. There is no shortage of ideas regarding the nature of both. While some candidates for DM are clearly ruled out, there is still a plethora of viable particles that fit the bill. In the context of DE, while current observations favour a cosmological constant picture, there are other competing models that are equally likely. This paper reviews the different possible candidates for DM including exotic candidates and their possible detection. This review also covers the different models for DE and the possibility of unified models for DM and DE. Keeping in mind the negative results in some of the ongoing DM detection experiments, here we also review the possible alternatives to both DM and DE (such as MOND and modifications of general relativity) and possible means of observationally distinguishing between the alternatives.

Introduction

One of the most unexpected revelations about our understanding of the universe is that the universe is not dominated by the ordinary baryonic matter, but instead, by a form of non-luminous matter, called the dark matter (DM), and is about five times more abundant than baryonic matter (Ade et al., 2014). While DM was initially controversial, it is now a widely accepted part of standard cosmology due to observations of the anisotropies in the cosmic microwave background, galaxy cluster velocity dispersions, large-scale structure distributions, gravitational lensing studies, and X-ray measurements from galaxy clusters.

Another unresolved problem in cosmology is that the detailed measurements of the mass density of the universe revealed a value that was 30% that of the critical density. Since the universe is very nearly spatially flat, as is indicated by measurements of the cosmic microwave background, about 70% of the energy density of the universe was left unaccounted for. This mystery now appears to be connected to the observation of the non-linear accelerated expansion of the universe deduced from independent measurements of Type Ia supernovae (Riess et al., 1998, Perlmutter et al., 1999, Peebles and Ratra, 2003, Sivaram, 2009).

Generally one would expect the rate of expansion to slow down, as once the universe started expanding, the combined gravity of all its constituents should pull it back, i.e. decelerate it (like a stone thrown upwards). So the deceleration parameter (q0) was expected to be a positive value. A negative q0 would imply an accelerating universe, with repulsive gravity and negative pressure. And the measurements of Type Ia supernovae have revealed just that. This accelerated expansion is attributed to the so-called dark energy (DE).

There are several experiments to detect postulated DM particles running for many years that have yielded no positive results so far. Only lower and lower limits for their masses are set with these experiments so far. The motto seems to be ‘absence of evidence is not evidence of absence’. But if future experiments still do not give any clue about the existence of DM, one may have to consider looking forward for alternate theories (Sivaram, 1994a, Sivaram, 1999).

The best example of this is that of the orbit and position of Vulcan, which was theoretically inferred from the observation of Mercury orbit (Hsu and Fine, 2005). The deviation of its orbit, as predicted by Newtonian gravity, was attributed to the missing planet (DM). But the resolution of this discrepancy came through the modification of Newtonian gravity by Einstein and not by DM. This is unlike in the case of Uranus were the prediction and discovery were successful using DM (Neptune) theory (Kollerstrom, 2001).

Section snippets

Observational evidence for dark matter

The evidence for the existence of such non-radiating matter goes back to more than eighty years ago, when Zwicky (1937) was trying to estimate the masses of large clusters of galaxies. Surprisingly it was found that the dynamical mass of the cluster, deduced from the motion of the galaxies (i.e. their dispersion of velocities), in a large cluster of galaxies were at least a hundred times their luminous mass. This led Zwicky to conclude that most of the matter in such clusters is not made up of

Dark energy

Various observations of the dynamics of the universe have implied the dominance of DE. This has led to the introduction of a repulsive gravity source to make the deceleration parameter negative (Jones and Lambourne, 2004). The dimensionless quantity, deceleration parameter q measures the cosmic acceleration of the universe’s expansion:q=-a¨aȧ2where ‘a’ is the scale factor of the universe.

All postulated forms of matter yield a deceleration parameter q0 (positive q), except in the case of DE.

Dark matter and dark energy

As of today, we don't know if dark matter and dark energy are manifestations of the same dark “thing”. For now, we think of them as separate entities. But the difference between the two is in the pressure exerted by them. The dark energy and cosmic repulsion is associated with negative pressure, given by:PDE=-ρc2Quantum vacuum energy exerts a negative pressure, contributing a cosmological constant term to gravity. But both ordinary matter (atoms, molecules, and photons) and dark matter exert

Alternate models to dark matter and dark energy

As mentioned earlier, if future experiments still do not give any clue about the existence of DM, one may have to consider looking forward for alternate theories to DM. These alternatives range from modification of Newtonian dynamics and modification of Newtonian gravity to modifying the Einstein-Hilbert action. These models are still not complete and even in the modified scenarios; some amount of DM is still required to account for certain observations.

Summary and outlook

In this review, we have given an overview of the current understanding of Dark Matter and Dark Energy, along with the possible alternative theories. The only observational evidence we have so far is that we require some amount of DM to account for certain observations, but we do not yet understand the nature of these particles. The proposed candidates range from WIMPS and Axions to exotic particles. This review covers the entire spectrum of these DM candidates highlighting the different

References (169)

  • R. Abbasi

    First neutrino point-source results from the 22-string IceCube detector

    Astrophys. J. Lett.

    (2009)
  • N. Abe et al.

    Anomaly-mediated supersymmetry breaking with axion

    J. High Energy Phys.

    (2002)
  • P.A.R. Ade

    Planck 2013 results. XVI. Cosmological parameters

    Astron. Astrophys.

    (2014)
  • S. Adrián-Martínez

    Searches for Point-like and extended neutrino sources close to the Galactic Centre using the ANTARES neutrino Telescope

    Astrophys. J. Lett.

    (2014)
  • R. Agnese

    New results from the search for low-mass weakly interacting massive particles with the CDMS low ionization threshold experiment

    Phys. Rev. Lett.

    (2016)
  • G.W. Angus et al.

    Can MOND take a bullet? Analytical comparisons of three versions of MOND beyond spherical symmetry

    Mon. Not. R. Astron. Soc.

    (2006)
  • M. Arik

    Search for sub-eV mass solar axions by the CERN axion solar telescope with 3He buffer gas

    Phys. Rev. Lett.

    (2011)
  • S.J. Asztalos

    SQUID-based microwave cavity search for dark-matter axions

    Phys. Rev. Lett.

    (2010)
  • G. Aad

    The ATLAS experiment at the CERN large hadron collider

    J. Instrum.

    (2008)
  • J. Bahcall

    Neutrino Astrophysics

    (1989)
  • E.A. Baltz et al.

    Detection of leptonic dark matter

    Phys. Rev. D

    (2003)
  • K. Barth

    CAST constraints on the axion-electron coupling

    J. Cosmol. Astropart. Phys.

    (2013)
  • K. Batygin et al.

    Evidence for a distant giant planet in the solar system

    Astron. J.

    (2016)
  • M.A. Beasley

    An overmassive Dark Halo around an ultra-diffuse Galaxy in the Virgo Cluster

    Astrophys. J.

    (2016)
  • C. Beck

    Possible resonance effect of axionic dark matter in Josephson junctions

    Phys. Rev. Lett.

    (2013)
  • J.D. Bekenstein

    Relativistic gravitation theory for the MOND paradigm

    Phys. Rev. D

    (2004)
  • J.D. Bekenstein

    Erratum: relativistic gravitation theory for the modified Newtonian dynamics paradigm

    Phys. Rev. D

    (2005)
  • E.F. Bell et al.

    Stellar mass-to-light ratios and the Tully-fisher relation

    Astrophys. J.

    (2001)
  • M.C. Bento et al.

    Generalized Chaplygin gas, accelerated expansion and dark energy-matter unification

    Phys. Rev. D

    (2002)
  • J. Beringer

    Review of particle physics

    Phys. Rev. D

    (2012)
  • G. Bertone et al.

    Dark matter dynamics and indirect detection

    Mod. Phys. Lett. A

    (2005)
  • C. Boehm

    MeV dark matter: has it been detected?

    Phys. Rev. Lett.

    (2004)
  • A. Boyarsky

    Unidentified line in X-ray spectra of the andromeda galaxy and perseus galaxy cluster

    Phys. Rev. Lett.

    (2014)
  • E. Bulbul

    Detection of an unidentified emission line in the stacked X-ray spectrum of galaxy clusters

    Astrophys. J.

    (2014)
  • M. Byrne et al.

    Bounds on charged, stable superpartners from cosmic ray production

    Phys. Rev. D

    (2002)
  • R.R. Caldwell et al.

    Phantom energy and cosmic doomsday

    Phys. Rev. Lett.

    (2003)
  • H.B. Callen

    Thermodynamics and an Introduction to Thermostatistics

    (1985)
  • B. Carr et al.

    Primordial black holes as dark matter

    Phys. Rev. D

    (2016)
  • J. Carson

    GLAST: physics goals and instrument status

    J. Phys: Conf. Ser.

    (2007)
  • M. Casse

    Gamma rays from the galactic bulge and large extra dimensions

    Phys. Rev. Lett.

    (2004)
  • S. Chaplygin

    Sci. Mem. Moscow Univ. Maths. Phys.

    (1904)
  • D. Cheng et al.

    Cosmological structure formation in Decaying Dark Matter models

    J. Cosmol. Astropart. Phys.

    (2015)
  • K.-Y. Choi et al.

    Decaying WIMP dark matter for AMS-02 cosmic positron excess

    Phys. Rev. D

    (2014)
  • T.E. Clarke

    Soft X-ray absorption due to a foreground edge-on spiral galaxy toward the core of A2029

    Astrophys. J.

    (2004)
  • D. Clowe

    A direct empirical proof of the existence of dark matter

    Astrophys. J. Lett.

    (2006)
  • S. Chatrchyan

    The CMS experiment at the CERN LHC

    J. Instrum.

    (2008)
  • C. Corda

    Interferometric detection of gravitational waves: the definitive test for General Relativity

    Int. J. Mod. Phys. D

    (2009)
  • H.J.M. Cuesta

    Hubble diagram of gamma-ray bursts calibrated with Gurzadyan-Xue cosmology

    Astron. Astrophys.

    (2008)
  • M. Davis

    The evolution of large-scale structure in a universe dominated by cold dark matter

    Astrophys. J.

    (1985)
  • E. Di Valentino

    Cosmological axion and neutrino mass constraints from Planck 2015 temperature and polarization data

    Phys. Lett. B

    (2015)
  • Cited by (0)

    View full text