DARK MATTER & DARK ENERGY | NEWS

DARK MATTER EXPERIMENT FINDS NO EVIDENCE OF AXIONS (28.03.2019)

All evidence for dark matter relies on its gravitational pull on baryons, and thus such evidence does not require any non-gravitational coupling between baryons and dark matter. Nonetheless, some small coupling can explain the comparable cosmic abundances of dark matter and baryons, as well as solving structure-formation puzzles in the pure cold-dark-matter models. Recent observations by the EDGES collaboration suggest that during the cosmic dawn, roughly 200 million years after the Big Bang, the baryonic temperature was half of its expected value. This observation is difficult to reconcile with the standard cosmological model but could be explained if baryons are cooled down by interactions with dark matter. Here we report that if a small fraction - less than one per cent - of the dark matter has a mini-charge, a million times smaller than the charge on the electron, and a mass in the range of 1-100 times the electron mass, then the data from the EDGES experiment can be explained while remaining consistent with all other observations. We also show that the entirety of the dark matter cannot have a

mini-charge.

 

Source: phys.org : https://phys.org/news/2019-03-dark-evidence-axions.html

A SMALL AMOUNT OF MINI-CHARGED DARK MATTER COULD COOL THE BARYONS IN THE EARLY UNIVERSE (2018)

All evidence for dark matter relies on its gravitational pull on baryons, and thus such evidence does not require any non-gravitational coupling between baryons and dark matter. Nonetheless, some small coupling can explain the comparable cosmic abundances of dark matter and baryons, as well as solving structure-formation puzzles in the pure cold-dark-matter models. Recent observations by the EDGES collaboration suggest that during the cosmic dawn, roughly 200 million years after the Big Bang, the baryonic temperature was half of its expected value. This observation is difficult to reconcile with the standard cosmological model but could be explained if baryons are cooled down by interactions with dark matter. Here we report that if a small fraction - less than one per cent - of the dark matter has a mini-charge, a million times smaller than the charge on the electron, and a mass in the range of 1-100 times the electron mass, then the data from the EDGES experiment can be explained while remaining consistent with all other observations. We also show that the entirety of the dark matter cannot have a

mini-charge.

 

Source: phys.org : https://www.nature.com/articles/s41586-018-0151-x

DARK MATTER LESS INFLUENTIAL IN GALAXIES IN EARLY UNIVERSE (2017)

New observations indicate that massive, star-forming galaxies during the peak epoch of galaxy formation, 10 billion years ago, were dominated by baryonic or “normal” matter. This is in stark contrast to present-day galaxies, where the effects of mysterious dark matter seem to be much greater.

 

Source: www.eso.org : https://www.eso.org/public/unitedkingdom/news/eso1709/?lang

NEUTRON STARS MAY HOLD AN ANSWER TO NEUTRON PUZZLE ON EARTH (pdf)

According to University of Illinois physicist Douglas H. Beck, "Neutrons play some unusual roles in our world. Free neutrons decay in about 900 s but, bound in nuclei, they are stable and make up somewhat more than half the mass of the visible universe."

Scientists use two different experimental methods to determine the value of τ, the neutron lifetime. Experiments that measure the products of neutron decay ‑ protons, electrons, and neutrinos ‑ tend to predict a longer lifetime than do experiments where the number of neutrons at a specific starting time and ending time are simply compared.

In January, theorists Bartosz Fornal and Ben Grinstein at UC San Diego posited that the difference could be explained by an "invisible" decay missed by the decay-product experiments; namely, that some 1 percent of the time, neutrons decay to dark matter particles that go undetected. Remarkably, the stability of ordinary nuclei does not completely rule out such a possibility.

Source : phys.org : 

https://phys.org/news/2018-08-neutron-stars-puzzle-earth.html?utm_source=nwletter&utm_medium=email&utm_campaign=daily-nwletter

Arman Shafieloo, Dhiraj Kumar Hazra, Varun Sahni, Alexei A. Starobinsky

METASTABLE DARK ENERGY WITH RADIOACTIVE-LIKE DECAY (pdf)

The new class of metastable dark energy (DE) phenomenological models proposed in which the DE decay rate does not depend on external parameters such as the scalefactor or the curvature of the Universe. Instead, the DE decay rate is assumed to be a constant depending only on intrinsic properties of DE and the type of a decay channel, similar to case of the radioactive decay of unstable particles and nuclei. Testing metastable DE models with observational data, we find that the decay half-life must be many times larger than the age of the Universe. Models in which DE decays into dark matter lead to lower values of the Hubble parameter at large redshifts relative to Λ cold dark matter (CDM). Consequently these models provide a better fit to cosmological BAO data (especially data from high-redshift quasars) than concordance (ΛCDM) cosmology.

Source:

- ArXiv.org

OXFORD Academic

 

 

DOING WITHOUT DARK ENERGY: MATHEMATICIANS PROPOSE ALTERNATIVE EXPLANATION FOR COSMIC ACCELERATION (pdf)

Three mathematicians have a different explanation for the accelerating expansion of the universe that does without theories of "dark energy." Einstein's original equations for General Relativity actually predict cosmic acceleration due to an "instability," they argue in paper published recently in Proceedings of the Royal Society A.

 

Source: phys.org :https://phys.org/news/2017-12-dark-energy-mathematicians-alternative-explanation.html  

Andre Maeder

DYNAMICAL EFFECTS OF THE SCALE INVARIANCE OF THE EMPTY SPACE: THE FALL OF DARK MATTER (pdf)

The hypothesis of the scale invariance of the macroscopic empty space, which intervenes through the cosmological constant, has led to new cosmological models. They show an accelerated cosmic expansion after the initial stages and satisfy several major cosmological tests. Developing the weak-field approximation, we find that the here-derived equation of motion corresponding to Newton's equation also contains a small outward acceleration term. The new term is thus particularly significant for very low density systems.

A modified virial theorem is derived and applied to clusters of galaxies. For the Coma Cluster and Abell 2029, the dynamical masses are about a factor of 5–10 smaller than in the standard case. This tends to leave no room for dark matter in these clusters. Thus, we tend to conclude that neither dark energy nor dark matter seems to be needed in the proposed theoretical context.

Standard model of the universe withstands most precise test by Dark Energy Survey. (2017)

The survey's researchers analyzed light from 26 million galaxies to study how structures in the universe have changed over the past 7 billion years - half the age of the universe.

The scientists used the fact that images of faraway galaxies get slightly distorted by the gravity of galaxies in the foreground - an effect known as weak gravitational lensing. This analysis led to the largest map ever constructed for the distribution of mass - both regular and dark matter - in the universe, as well as its evolution over time.

 

 

Cosmologists produce new maps of dark matter dynamics. (2017)

 

Using advanced computer modelling techniques, the research team has translated the distribution of galaxies into detailed maps of matter streams and velocities for the first time, which allows us to estimate the distribution of "dark matter" in the universe.

 

 

Can we ditch dark energy by better understanding general relativity? (2017)

 

In standard cosmology, we assume a Univerce expanding as if there were no cosmic structures. We then do computer simulations using only Newton's 330-year old theory. This produces a structure resembling the observed cosmic web in a reasonably compelling fashion. But it requires including dark energy and dark matter as ingredients. Further, standard cosmology also fixes the curvature of space to be uniform everywhere, and decoupled from matter. But that's at odds with Einstein's basic idea that matter tells space how to curve.

Since the early 2000s, some cosmologists have been exploring the idea that while Einstein's equations link matter and curvature on small scales, their large-scale average might give rise to backreaction – average expansion that's not exactly homogeneous.

Matter and curvature distributions start out near uniform when the universe is young. But as the cosmic web emerges and becomes more complex, the variations of small-scale curvature grow large and average expansion can differ from that of standard cosmology.

Recent numerical results of a team in Budapest and Hawaii that claim to dispense with dark energy used standard Newtonian simulations. But they evolved their code forward in time by a non-standard method to model the backreaction effect.

 

 

Explaining the accelerating expansion of the universe without dark energy. (2017)

 

Enigmatic 'dark energy', thought to make up 68% of the universe, may not exist at all, according to a Hungarian-American team. The researchers believe that standard models of the universe fail to take account of its changing structure, but that once this is done the need for dark energy disappears. In practice, normal and dark matter appear to fill the universe with a foam-like structure, where galaxies are located on the thin walls between bubbles, and are grouped into superclusters. The insides of the bubbles are in contrast almost empty of both kinds of matter. Using a computer simulation to model the effect of gravity on the distribution of millions of particles of dark matter, the scientists reconstructed the evolution of the universe, including the early clumping of matter, and the formation of large scale structure. Unlike conventional simulations with a smoothly expanding universe, taking the structure into account led to a model where different regions of the cosmos expand at different rate. The average expansion rate though is consistent with present observations, which suggest an overall acceleration.

 

 

Physicists have doubted the possibility of the existence of "lightweight" dark matter. (2016) (In Russian)

 

As scientists explain, axions, if they really exist, should interact in a special way with photons, light particles, if they pass through strong magnetic fields existing in the vicinity of central black holes in galaxies or in magnetars and other "magnetized" compact objects. But, as observations of the space gamma-telescope "Fermi" have shown, there are no traces of the fact that the axions can somehow influence the behavior of photons. This means that the axions either do not exist, or that their mass is much larger than previously thought. The second scenario is unlikely, but in principle it is possible - in this case the dark matter would consist only of axions, and not any other particles. The verification of such a theory will require the construction and launching into space of new telescopes capable of operating at higher energies than Fermi.

 

 

Project "Pamela": ten years in search of dark matter. (2016) (In Russian)

 

Starting from June 15, 2006, MEPHI scientists consistently measured the characteristics of cosmic particles (electrons and positrons, protons and antiprotons and light nuclei). As a result of painstaking analysis of materials, it was found that the positron flux behaves differently than predicted by theoretical calculations. The share of positrons increases in cosmic radiation relative to ordinary particles to electrons. This could be associated with hypothetical particles "WIMPs", of which dark matter is supposedly composed. When colliding with one another, WIMPs can annihilate, turning into known particles, for example, into protons and antiprotons, electrons and positrons. But during the measurements with the magnetic spectrometer "Pamela" it became clear that the WIMPs can also disintegrate themselves, turning into the same well-known particles.

The data obtained in 2008 with the help of the Pamela magnetic spectrometer were later confirmed twice by other experiments in space - on the Gamma-telescope Fermi and on the AMS-02 magnetic spectrometer.

 

A high stellar velocity dispersion and ~100 globular clusters for the ultra-diffuse galaxy "Dragonfly 44". (2016)

 

The high mass of "Dragonfly 44" is accompanied by a large globular cluster population. Our results add to other recent evidence that many ultra-diffuse galaxies are "failed" galaxies with the sizes, dark matter content and globular cluster systems of much more luminous objects. The dark matter fraction of "Dragonfly 44" is about 98%.

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Explaining the accelerating expansion of the universe without dark energy (30.03.2017)

Enigmatic 'dark energy', thought to make up 68% of the universe, may not exist at all, according to a Hungarian-American team. The researchers believe that standard models of the universe fail to take account of its changing structure, but that once this is done the need for dark energy disappears. The team publish their results in a paper in Monthly Notices of the Royal Astronomical Society. 

 

Source: Phys.org: https://phys.org/news/2017-03-expansion-universe-dark-energy.html

A high stellar velocity dispersion and ~100 globular clusters for the ultra-diffuse galaxy "Dragonfly 44"

 

(Pieter van Dokkum, Roberto Abraham, Jean Brodie, Charlie Conroy, Shany Danieli, Allison Merritt, Lamiya Mowla, Aaron Romanowsky and Jielai Zhang) (2016)

 

The high mass of Dragonfly 44 is accompanied by a large globular cluster population. Our results add to other recent evidence that many ultra-diffuse galaxies are "failed" galaxies with the sizes, dark matter content and globular cluster systems of much more luminous objects. The dark matter fraction of Dragonfly 44 is about 98%.

 

 

Team simulates a magnetar to seek dark matter particle (2016)

 

In a paper published online in Physical Review Letters, the MIT team proposes an experiment to detect axions by simulating an extreme astrophysical phenomenon known as a magnetar—a type of neutron star that generates an immensely powerful magnetic field. The physicists reasoned that in the presence of an axion such a huge magnetic field should waver ever so slightly, producing a second, vastly smaller magnetic field as a signature of the axion itself.

 

 

The CERN has launched its hunt of the mysterious « dark photons » (2016) (In Russian)

 

The presence of dark matter is betrayed only by its gravitational effect, this is how modern science generally knows about its existence. Leading physicists at the CERN have set out to discover the so-called “dark photon”, a hypothetical elementary particle which is allegedly analogous to the photons for dark matter. 

 

Scientists from South Africa have catched signs of the heavy boson " Madala”, which interacts with both normal and dark matter (2016) (In Russian)

 

Two separate experiments on the ATLAS detector and the Compact Muon Solenoid (CMS), at the large Hadron Collider (LHC, CERN), suggest the existence of a new elementary particle weighing some 270 GeV.

 

If its existence is confirmed, this particle will bring us closer to solving one of the biggest mysteries of the universe — what is dark matter. Madala could become the first known particle, which can interact with dark matter.

 

See also, in English : https://www.sciencealert.com/physicists-have-caught-signs-of-a-brand-new-particle-the-madala-boson

 

 

Axion alert! Exotic-particle detector may miss out on dark matter. (2016)

 

An ambitious supercomputer calculation has brought good and bad news for physicists hunting the "axion" — a hypothetical particle that is considered a leading candidate for dark matter. The result shows that the axion, if it exists, could be at least ten times heavier than previously thought. If true, that’s a useful clue on how to find the particle. But it also suggests that an experiment that has been hunting the axion for two decades might be unlikely to find it, because the detector was designed to search for a lighter version.

 

 

Controversial declaration about the discovery of dark matter will finally be checked with decisive experiments (2016) (In Russian)

 

The original statement was made by the collaboration DAMA, which is located in a lab deep beneath the Gran Sasso mountain, to the East of Rome. More than a decade ago, it has provided preliminary evidence of the discovery of dark matter. In the next five years additional similar detectors will be built in Korea, Australia, Spain and Italy. They will all be used to search for dark matter when monitoring micro-blasts during collisions of particles in crystals of sodium iodide.

 

 

A look at WIMPs : let’s study alternative theories for dark matter (2016) (In Russian)

Many scientists assumed that the dark matter consists of weakly interacting massive particles (WIMP), whose mass is approximately 100 times greater than the mass of the proton, but which interact as neutrinos. Nevertheless, all attempts to find WIMPs during experiments in particle accelerators were unsuccessful. So scientists began sorting through possible alternatives to the composition of dark matter.

 

 

Two new methods have been proposed in the search for dark energy (2016) (In Russian)

 

Where is the dark matter? Scientists who hunt for decades for these ephemeral substance, if it can be called such way, are beginning to worry that they are looking for it not in the right place. So far the search for dark matter have focused largely on "weakly interacting massive particles" (WIMP) — theoretical particles weighing between 1 GeV and 1 TeV, between 1 and 1000 masses of the proton. But there are larger areas available for the existence of dark matter, as particles with a smaller mass.

 

 

The world’s most sensitive detector didn’t find dark matter (2016) (In Russian)

 

The incredibly sensitive dark matter detector LUX, lying under one kilometer of rocks, haven't found anything during 20 months of search for dark matter : this has substantially narrowed the range of possible properties of mysterious substances.

 

 

New idea proposed for the search of light dark matter particles (2015) (In Russian)

 

The search of dark matter particles with a mass less than 1 GeV is an exceptionally difficult technical task. None of the existing detectors is sensible to such particles. In this article, American theorists proposed the idea of a new superconducting detector which would be able to “feel” dark matter particles with masses in the MeV, or even in the keV, ranges, thus expanding the scope of searches by 4 - 5 orders of magnitude.

 

 

NASA: the Earth may have its own « beard » made of dark matter (2015) (In Russian)

Using computer simulations, NASA scientists found out what happens when the "threads" of dark matter particles approach the Earth. The analysis revealed that the particles’ flux is concentrated in ultradense threads, or “hairs”, of dark matter. As a result, there should be pretty much of such hairs, which stretch out from the Earth’s ground (like a “beard”).

Computer simulations also showed that changes in density, which occur inside the Earth — from its internal core to the mantle and the crust — will be reflected on these "hairs".

 

 

Dark matter may have been detected – streaming from the sun’s core. (2014)

 

Researchers at Leicester University spotted the curious signal in 15 years of measurements taken by the European Space Agency’s orbiting XMM-Newton observatory. They noticed that the intensity of x-rays recorded by the spacecraft rose by about 10% whenever it observed the boundary of Earth’s magnetic field that faces towards the sun.

The x-ray background – the sky, after the bright x-ray sources are removed – appears to be unchanged whenever you look at it. The seasonal signal in this x-ray background, which has no conventional explanation was discovered, that is consistent with the discovery of axions.

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