Archivi tag: Standard Cosmological Model

Massive or massless neutrinos?

Gli scienziati avrebbero risolto uno dei problemi aperti dell’attuale modello cosmologico standard combinando i dati del satellite Planck e quelli ottenuti grazie al fenomeno della lente gravitazionale allo scopo di determinare la massa dei neutrini.

The team, from the universities of Nottingham and Manchester, used observations of the Big Bang and the curvature of spacetime to accurately measure the mass of these elementary particles for the first time. The recent Planck spacecraft observations of the Cosmic Microwave Background (CMB), the fading glow of the Big Bang, highlighted a discrepancy between these cosmological results and the predictions from other types of observations. The CMB is the oldest light in the Universe, and its study has allowed scientists to accurately measure cosmological parameters, such as the amount of matter in the Universe and its age. But an inconsistency arises when large-scale structures of the Universe, such as the distribution of galaxies, are observed. Dr Adam Moss, from The University of Nottingham’s School of Physics and Astronomy said: “We observe fewer galaxy clusters than we would expect from the Planck results and there is a weaker signal from gravitational lensing of galaxies than the CMB would suggest. A possible way of resolving this discrepancy is for neutrinos to have mass. The effect of these massive neutrinos would be to suppress the growth of dense structures that lead to the formation of clusters of galaxies.” Neutrinos interact very weakly with matter and so are extremely hard to study. They were originally thought to be massless but particle physics experiments have shown that neutrinos do indeed have mass and that there are several types, known as flavours by particle physicists. The sum of the masses of these different types has previously been suggested to lie above 0.06 eV (much less than a billionth of the mass of a proton). Dr Moss and Professor Richard Battye from The University of Manchester have combined the data from Planck with gravitational lensing observations in which images of galaxies are warped by the curvature of spacetime.

They conclude that the current discrepancies can be resolved if massive neutrinos are included in the standard cosmological model.

They estimate that the sum of masses of neutrinos is 0.320 +/- 0.081 eV (assuming active neutrinos with three flavours). Professor Battye added: “If this result is borne out by further analysis, it not only adds significantly to our understanding of the sub-atomic world studied by particle physicists, but it would also be an important extension to the standard model of cosmology which has been developed over the last decade”.

Nottingham University: Massive neutrinos solve a cosmological conundrum

arXiv: Evidence for massive neutrinos from CMB and lensing observations

A holographic origin for the Big Bang

Un gruppo di fisici teorici hanno pubblicato un articolo in cui propongono una nuova idea che spiegherebbe l’origine dell’Universo. Secondo gli scienziati, è possibile che lo spazio e il tempo vennero creati dal collasso quadridimensionale di una stella che spazzò i detriti nel cosmo per poi trasformarsi in un buco nero.

As it stands, the prevailing theory states the Universe was born from an infinitely dense singularity through some currently unknown mechanism. Actually, the entire big bang event itself is entirely unknown. Our equations have yet to be complete enough to describe the moment of creation, a revelation physicists think will follow the discovery of the theory of everything (which scientists might be one-step closer to doing). Until then, what happened “before the big bang,” the nature of the ‘singularity’ that caused the big bang, and the event itself will remain unknown without some major scientific breakthrough. At the moment, it’s anyone’s guess what happened. (Important side note: we have a lot of knowledge and experimental evidence talking about what happened immediately after the big bang, up to about 10-35 or so seconds after the event, so our timeline for cosmology is still preserved.) The standard big bang theory has some limitations and some serious problems. It’s limitations are mostly summed up by our inability to mathematically or practically study the big bang singularity, as mentioned before. On the flip side, the big bang theory doesn’t really explain why the Universe has a nearly uniform temperature (that’s where inflation theory comes in, which suggests that the Universe went through a period of rapid, faster-than-light expansion in its early history).

This new model is based on the slightly older idea that our Universe is basically a three-dimensional membrane floating in a fourth-dimensional “bulk universe.” That’s the basic idea that’s supporting this new model.

The tenets for the new theory are as follows:

  • The “bulk universe” has fourth-dimensional stars that go through the same life cycle that our three-dimensional stars go through.
  • Just as with our stars, the stars in the bulk universe could go supernova and collapse into a black hole.
  • This is where things start to get really cool. Just as our three-dimensional black holes have event horizons that appear two-dimensional, it’s plausible that the fourth-dimensional black holes have event horizons that appear three-dimensional.
  • This three-dimensional event horizon is knows as a hypersphere. This is the region of space in which our Universe exists.

This new way of looking at the Universe has some strong points in its favor. The model is able to explain the expansion of the Universe and is able to describe the Universe’s nearly uniform temperature, with one (rather large) limitation. The model disagrees with observations made by the Planck telescope, which recently created the most detailed map we have of the cosmic microwave background (post). The hypersphere model has about a four percent discrepancy, which means the hypersphere needs to be refined before it’ll gain any credence.

This new model could go a long way to helping us understand the nature of inflation.

Currently, the only thing we really know about inflation is that “it’s happening.” We don’t know why or how, but the named mechanism for it is known as dark energy. The model proposes that inflation is caused by the Universe’s motion through higher dimensions of space. It’s important to note that the paper where this study was published does not state whether the paper has been submitted to peer review. So, whereas the hypersphere idea is fantastic and fun, it has a long way to go before we can considered a viable hypothesis.

From Quarks to Quasars: Revising the Big Bang? New Theory on Creation.
arXiv: Out of the White Hole: A Holographic Origin for the Big Bang

Is the Universe really expanding?

Un cosmologo dell’Università di Heidelberg, Christof Wetterich, ritiene che il modello relativo all’espansione dell’Universo, ossia il modello cosmologico standard, potrebbe essere errato. Egli suggerisce che il redshift, cioè lo spostamento verso il rosso misurato dagli astronomi, sarebbe dovuto ad un incremento della massa presente nell’Universo.

For nearly a century, the consensus among astrophysicists has been that the Universe started with a Big Bang and has been expanding ever since. This hypothesis formed because researchers found that in analyzing the light emitted from stars, a redshift occurred, where its frequency changes as an object that emits light moves away from us.

But Wetterich says the redshift might me due to something else, an increase in the total mass in the universe.

Wetterich’s idea is that light emitted from an atom is governed by the mass of its particles, if that atom were to become larger in mass, the light that it emits would change in frequency as its electrons became more energetic. More energy would appear as light moving toward the blue spectrum, while less energy (an atom losing mass), would move toward the red spectrum. Thus, Wetterich reasons, if the mass of observable objects were once less, we would now see them with a redshift as they expand.

If his line of reasoning is true, Wetterich says it’s possible that the Universe is actually contracting.

Wetterich’s paper hasn’t been peer reviewed yet, but thus far, comments by others in the field suggest openness to this new line of thinking. That might be because one exciting prospect of this new theory is that it would do away with the idea of a singularity existing just before the Big Bang, a point at which conventional physics breaks down. Instead it might suggest that the Universe is simply in a constant state of flux with no real beginning and no real end. Unfortunately, Wetterich’s theory can’t be tested because of the relative nature of mass. Everything we are able to see has a mass that is relative in size to everything else. Thus if it’s all growing, we wouldn’t have anything to measure it against to see that it’s happening.

Nature: Cosmologist claims Universe may not be expanding
arXiv: A Universe without expansion

Large galaxy clusters contain the right proportion of visible matter

Grazie ad uno studio recente condotto da alcuni ricercatori della University of Alabama in Huntsville (UAH) guidati da Massimiliano Bonamente, i barioni, che costituiscono la materia visibile nell’Universo e che si riteneva un tempo assente dagli ammassi di galassie, sono presenti in accordo alle proporzioni attese dal modello cosmologico standard negli ammassi di galassie più grandi e luminosi.

The new research studied very large galaxy clusters and concludes that they indeed contain the proportion of visible matter that is being worked out as part of the Big Bang Theory.

The work may prompt new efforts to explain past research findings that some clusters have a deficit in baryons from what is expected.

The Universe is composed of about 75 percent dark energy and 25 percent matter. Of the portion that is matter, about 16 percent is the familiar visible matter that is all around us and the remaining 84 percent is dark matter. “We call it dark matter because we don’t know what it is made of, but it is made of some type of particles and it doesn’t seem to emit visible energy”, said Bonamente. Together dark energy, dark matter and ordinary baryonic matter form a pie chart of the mass of the Universe, where everything has to add up to 100 percent. “We don’t know what dark matter is”, he said, “but we have the means to put the pie together”. While dark energy has a repulsive energy, dark matter and baryonic matter have an attractive force where “everything likes to clump together” to form stars and planets and galaxies. Using x-rays, astrophysicists discovered that there is a diffuse hot plasma gas that fills the space between galaxies. “Basically, the space between galaxies is filled with this hot plasma that is 100 million degrees in temperature”, said Bonamente. Because the gas is so diffuse, it has very low heat capacity. “It is like if I posed this question to you: Which would you rather put your finger in, a boiling cup of water or a room that had been heated to 212 degrees Fahrenheit? You choose the room because the temperature inside it is more diffused than it would be in the concentrated cup of water, and so you can tolerate it”. So why doesn’t the hot gas simply escape? “It is bound to the cluster by gravity”, said Bonamente. “With hot gas, you can do two things. You can measure the regular matter, which is the baryon content. And two, since the hot gas is bound, you can measure how much matter it would take to hold the gas and therefore you can tell how much dark matter there is. “All of a sudden, there is something really wonderful about the hot gas”, he said. “You can have your cake and eat it, too”. Theoretically, the Universe should contain the same proportions of visible and dark matter regardless of where it is sampled. Using cosmic microwave radiation readings, astrophysicists have been able to do a type of forensics of the Universe’s past, and those findings have shown the proportions that were present at the Big Bang or shortly thereafter (post). “Because it started in the Big Bang, that ratio should persist”, Bonamente said. “It is like if I go to the ocean with a scoop. The scoop of water I get should have the same concentration of salt as the rest of the ocean, no matter where I get it”.

But past research had indicated that some clusters were short on the expected percentage of baryons, posing the question of where they were.

Since recently, people believed that clusters had less than 16 percent of baryons, so there were missing baryons”, Bonamente said. “We said no, they are there. So, how did we find clusters with this correct ratio? We studied the most luminous ones, because they have more mass and retain more baryons”.

The findings could open new areas of investigation into why the deficits in baryons were recorded in past research.

Bonamente suggests one theory. “We know that some smaller clusters do have lower concentrations of baryons than the larger ones”, he said. Perhaps because of weaker gravitational forces, the hot gases escaped in similar fashion as planets that have no atmosphere. “Maybe the gas can be bound but maybe a little bit can fly off if there is just not quite enough gravity”. For further studies on smaller clusters, Bonamente looks forward to the arrival of new faculty member Ming Sun, formerly at the University of Virginia, who is an expert on groups having less than 16 percent baryons. “I am excited that Ming has decided to join our research group”, says Bonamente. “With him on board, UAH is poised to continue making discoveries on the makeup of the universe, and that is the most exciting question to answer that I can think of”.

UAH: UAH findings on makeup of universe may spawn new research
arXiv: Chandra Measurements of a Complete Sample of X-ray Luminous Galaxy Clusters: the Gas Mass Fraction

The New Standard Model of the Universe

The new concordance model in agreement with observations: ΛWDM (Lambda-dark energy- Warm Dark Matter). Recently, Warm (keV scale) Dark Matter emerged impressively over CDM (Cold Dark Matter) as the leading Dark Matter candidate. Astronomical evidence that Cold Dark Matter (LambdaCDM) and its proposed tailored cures do not work at galactic and small scales is staggering. LambdaWDM solves naturally the problems of LambdaCDM and agrees remarkably well with the observations at galactic and small as well as large and cosmological scales. In contrast, LambdaCDM simulations only agree with observations at large scales. In the context of this new Dark Matter situation, which implies novelties in the astrophysical, cosmological and keV particle physics context, this 17th Paris Colloquium 2013 is devoted to the LambdaWDM Standard Model of the Universe.

This Colloquium is within the astrofundamental physics spirit of the Chalonge School, focalised on recent observational and theoretical progress in the CMB, dark matter, dark energy, the new WDM framework to galaxy formation, and the theory of the early universe inflation with predictive power in the context of the LambdaWDM Standard Model of the Universe. The Colloquium addresses as well the theory and experimental search for the WDM particle physics candidates (keV sterile neutrinos). Astrophysical constraints including sterile neutrino decays points the sterile neutrino mass m around 2 keV. WDM predictions for EUCLID and PLANCK start to be available. MARE and an adapted KATRIN experiment could detect a keV sterile neutrino. A formidable WDM work to perform is ahead of us. In summary, the aim of the meeting is to put together real data : cosmological, astrophysical, particle, nuclear physics data, and hard theory predictive approach connected to them in the framework of the LambdaWDM Standard Model of the Universe.

Context, CDM crisis and the CDM decline: On large cosmological scales, CDM agrees in general with observations but CDM does not agree with observations on galaxy scales and small scales. Over most of twenty years, increasing number of cyclic arguments and ad-hoc mechanisms or recipes were-and continue to be- introduced in the CDM galaxy scale simulations, in trying to deal with the CDM small scale crisis: Cusped profiles and overabundance of substructures are predicted by CDM. Too many satellites are predicted by CDM simulations while cored profiles and no such overabundant substructures are seen by astronomical observations. Galaxy formation within CDM is increasingly confusing and in despite of the proposed cures, does not agree with galaxy observations. On the CDM particle physics side, the situation is no less critical: So far, all the dedicated experimental searches after most of twenty years to find the theoretically proposed CDM particle candidate (WIMP) have failed. The CDM indirect searches (invoking CDM annihilation) to explain cosmic ray positron excesses, are in crisis as well, as wimp annihilation models are plagued with growing tailoring or fine tuning, and in any case, such cosmic rays excesses are well explained and reproduced by natural astrophysical process and sources. The so-called and repeatedly invoked ‘wimp miracle’ is nothing but being able to solve one equation with three unknowns (mass, decoupling temperature, and annihilation cross section) within wimp models theoretically motivated by SUSY model building twenty years ago (at that time those models were fashionable and believed for many proposals). After more than twenty years -and as often in big-sized science-, CDM research has by now its own internal inertia: growing CDM galactic simulations involves large super-computers and large number of people working with, without agreement with the observations ; CDM particle wimp search involve large and long-time planned experiments, huge number of people, (and huge budgets) without producing wimp detection; one should not be surprised in principle, if a fast strategic change would not yet operate in the CDM and wimp research, although its interest would progressively decline.

Topics

  • Observational and theoretical progress on the nature of dark matter : keV scale warm dark matter
  • Cored density profiles in agreement with observations.
  • Large and small scale structure formation in agreement with observations at large scales and small (galactic) scales.
  • Warm (keV scale) dark matter from theory and observations.
  • The new quantum mechanical framework to galactic structure. WDM core sizes in agreement with observations.
  • Supermassive Black Holes : Theory and Observations. The clarifing and unifying WDM framework for stars, galaxies and cosmology.
  • Warm (keV scale) dark matter N-body simulations in agreement with observations.
  • Neutrinos in astrophysics and cosmology.
  • The new serious dark matter candidate: Sterile neutrinos at the keV scale.
  • Neutrinos mass bounds from cosmological data and from high precision beta decay experiments.
  • Dark energy: cosmological constant: the quantum energy of the cosmological vacuum.
  • The analysis of the CMB+LSS+SN data with the effective (Ginsburg-Landau) effective theory of inflation: New Inflation (double well inflaton potential) strongly favored by the CMB + LSS + SN data.
  • The presence of the lower bound for the primordial gravitons (non vanishing tensor to scalar ratio r) with the present CMB+LSS+SN data.
  • CMB news and polarization. Forecasts and Planck results.