Archivi tag: gravity

Observational anomalies challenging the Lambda-CDM cosmological model

In the current paradigm of the Lambda-CDM cosmology, the fundamental properties of the Universe are believed to be well understood, with only minor adjustment of the basic model being left to be done. The global picture of an expanding Universe originating during a singularity at Big Bang is now taken for granted, and some basic properties of the Universe are considered to be known with amazing accuracy. For instance, according to Lambda-CDM concordance cosmology, the age of the Universe is 13.798±0.037 Gyr, quoted with a precision higher than the one with which we know the age of our planet. Continua a leggere Observational anomalies challenging the Lambda-CDM cosmological model

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Testing Gravity

A three day workshop on various ways of testing gravity (cosmological, astrophysical and terrestrial). This is a topical theme, in part because of the growing interest in modified gravity theories motivated by the unexplained nature of dark matter and dark energy, and in part by improving technologies that open opportunities for new types of tests. Continua a leggere Testing Gravity

99 years of Black Holes: from Astronomy to Quantum Gravity

This meeting shall bring together the Black Hole community (from Quantum to supermassive) as well as the Gravitational Wave Community. The main topics of the conference will cluster around Black Holes, Gravitational Waves and the Future of General Relativity and Quantum Physics.
Continua a leggere 99 years of Black Holes: from Astronomy to Quantum Gravity

Frontier Objects in Astrophysics and Particle Physics

We announce the XV Vulcano Workshop, which will be held from May 18th to May 24th, 2014 in the Vulcano Island (Sicily, Italy). As in the past editions, the workshop will aim to gather people from High Energy Astrophysics and Particle Physics to discuss the most recent highlights in these fields.

The workshop will cover the following topics:

  • Astrophysics/Cosmology
  • Astrophysics/Gravity
  • Dark Matter
  • Particle Physics
  • Cosmic Rays
  • Gamma/Neutrino Astronomy
  • Neutrinos
  • Future Prospects

Neutrons method to test dark energy theories by sensitive measurements of gravity at small scales

Schema dello spettrometro di risonanza per lo studio degli effetti della gravità su scale molto piccole. Credit: TU
Non sempre occorre un acceleratore di particelle per fare esperimenti di fisica fondamentale. I primi risultati di un esperimento a bassa energia sulla gravità newtoniana, spinto fino ad un limite più piccolo di cinque ordini di grandezza, stringono il cerchio sulle proprietà potenziali che forze e particelle potrebbero assumere al di là di questo limite di sensibilità pari ad almeno qualche centinaia di migliaia di volte. Infatti, un nuovo metodo sviluppato da alcuni fisici della Vienna University of Technlogy, denominato spettroscopia di risonanza gravitazionale, si è rivelato così sensibile che ora potrà essere applicato per studiare le due componenti più enigmatiche dell’Universo, la materia scura e l’energia scura.

All the particles we know to exist make up only about five per cent of the mass and energy of the Universe. The rest, dark matter and dark Energy, remains mysterious. A European collaboration led by researchers from the Vienna University of Technology has now carried out extremely sensitive measurements of gravitational effects at very small distances at the Institut Laue-Langevin (ILL) in Grenoble. These experiments provide limits for possible new particles or fundamental forces, which are a hundred thousand times more restrictive than previous estimations.

Undiscovered Particles?
Dark matter is invisible, but it acts on matter by its gravitational pull, influencing the rotation of galaxies. Dark energy, on the other hand, is responsible for the accelerated expansion of the Universe. It can be described by introducing a new physical quantity, Albert Einstein’s cosmological constant. Alternatively, so-called quintessence theories have been put forward: “Perhaps empty space is not completely empty after all, but permeated by an unknown field, similar to the Higgs-field”, says Professor Hartmut Abele (TU Vienna), director of the Atominstitut and group leader of the research group. These theories are named after Aristotle’s “quintessence”, a hypothetical fifth element, in addition to the four classical elements of ancient Greek philosophy. 

If new kinds of particles or additional forces of nature exist, it should be possible to observe them here on Earth.

Tobias Jenke and Hartmut Abele from the Vienna University of Technology developed an extremely sensitive instrument, which they used together with their colleagues to study gravitational forces. Neutrons are perfectly suited for this kind of research. They do not carry electric charge and they are hardly polarizable. They are only influenced by gravity, and possibly by additional, yet unknown forces. 


Forces at Small Distances
The technique they developed takes very slow neutrons from the strongest continuous ultracold neutron source in the world, at the ILL in Grenoble and funnels them between two parallel plates. According to quantum theory, the neutrons can only occupy discrete quantum states with energies which depend on the force that gravity exerts on the particle. By mechanically oscillating the two plates, the quantum state of the neutron can be switched. That way, the difference between the energy levels can be measured. This work is an important step towards modelling gravitational interactions at very short distances. The ultracold neutrons produced at ILL together with the measurement devices from Vienna are the best tool in the world for studying the predicted tiny deviations from pure Newtonian gravity”, says Peter Geltenbort (ILL Grenoble)Different parameters determine the level of precision required to find such tiny deviations, for instance the coupling strength between hypothetical new fields and the matter we know. Certain parameter ranges for the coupling strength of quintessence particles or forces have already been excluded following other high-precision measurements. But all previous experiments still left a large parameter space in which new physical non-Newtonian phenomena could be hidden.

A Hundred Thousand Times Better than Other Methods
The new neutron method can test theories in this parameter range: “We have not yet detected any deviations from the well-established Newtonian law of gravity”, says Hartmut Abele. “Therefore, we can exclude a broad range of parameters”. The measurements determine a new limit for the coupling strength, which is lower than the limits established by other methods by a factor of a hundred thousand. Even if the existence of certain hypothetical quintessence particles is disproved by these measurements, the search will continue as it is possible that new physics can still be found below this improved level of accuracy. Therefore, Gravity Resonance Spectroscopy will need to be improved further, and increasing the accuracy by another few orders of magnitude seems feasible to the Abele’s team.

However, if even that does not yield any evidence of deviations from known forces, Albert Einstein would win yet another victory: his cosmological constant would then appear more and more plausible.

TU: Searching for Dark Energy with Neutrons
arXiv: Gravity Resonance Spectroscopy Constrains Dark Energy and Dark Matter Scenarios

Using the Universe as ‘tool’ to detect gravitons

La gravità è l’unica tra le quattro forze fondamentali per la quale gli scienziati non hanno ancora rivelato la sua unità fondamentale. Infatti, secondo il modello standard delle particelle elementari si ritiene che l’interazione gravitazionale venga trasmessa attraverso il gravitone, allo stesso modo con cui l’interazione elettromagnetica viene trasmessa dai fotoni. Oggi, nonostante esistano delle basi teoriche a favore dell’esistenza dei gravitoni rimane, però, il problema di rivelarli, almeno sulla Terra dove le possibilità sono estremamente basse se non quasi nulle.

For example, the conventional way of measuring gravitational forces, by bouncing light off a set of mirrors to measure tiny shifts in their separation, would be impossible in the case of gravitons. According to physicist Freeman Dyson, the sensitivity required to detect such a miniscule distance change caused by a graviton requires the mirrors to be so massive and heavy that they’d collapse and form a black hole. Because of this, some have claimed that measuring a single graviton is hopeless. But what if you used the largest entity you know of, in this case the Universe, to search for the telltale effects of gravitons. That is what two physicists are proposing. In the paper, “Using cosmology to establish the quantization of gravity”, published in Physical Review D (Feb. 20, 2014), Lawrence Krauss, a cosmologist at Arizona State University, and Frank Wilczek, a Nobel-prize winning physicist with MIT and ASU, have proposed that measuring minute changes in the cosmic background radiation of the Universe could be a pathway of detecting the telltale effects of gravitons.

Krauss and Wilczek suggest that the existence of gravitons, and the quantum nature of gravity, could be proved through some yet-to-be-detected feature of the early Universe.

This may provide, if Freeman Dyson is correct about the fact that terrestrial detectors cannot detect gravitons, the only direct empirical verification of the existence of gravitons”, Krauss said. “Moreover, what we find most remarkable is that the Universe acts like a detector that is precisely the type that is impossible or impractical to build on Earth”. It is generally believed that in the first fraction of a second after the Big Bang, the Universe underwent rapid and dramatic growth during a period called “inflation.” If gravitons exist, they would be generated as “quantum fluctuations” during inflation. Ultimately, these would evolve, as the Universe expanded, into classically observable gravitational waves, which stretch space-time along one direction while contracting it along the other direction. This would affect how electromagnetic radiation in the cosmic microwave background (CMB) radiation left behind by the Big Bang is produced, causing it to become polarized. Researchers analyzing results from the European Space Agency’s Planck satellite are searching for this “imprint” of inflation in the polarization of the CMB.

Krauss said his and Wilczek’s paper combines what already is known with some new wrinkles.

While the realization that gravitational waves are produced by inflation is not new, and the fact that we can calculate their intensity and that this background might be measured in future polarization measurements of the microwave background is not new, an explicit argument that such a measurement will provide, in principle, an unambiguous and direct confirmation that the gravitational field is quantized is new”, he said. “Indeed, it is perhaps the only empirical verification of this very important assumption that we might get in the foreseeable future”. Using a standard analytical tool called dimensional analysis, Wilczek and Krauss show how the generation of gravitational waves during inflation is proportional to the square of Planck’s constant, a numerical factor that only arises in quantum theory. That means that the gravitational process that results in the production of these waves is an inherently quantum-mechanical phenomenon. This implies that finding the fingerprint of gravitational waves in the polarization of CMB will provide evidence that gravitons exist, and it is just a matter of time (and instrument sensitivity) to finding their imprint. “I’m delighted that dimensional analysis, a simple but profound technique whose virtues I preach to students, supplies clear, clean insight into a subject notorious for its difficulty and obscurity”, said Wilczek. “It is quite possible that the next generation of experiments, in the coming decade or maybe even the Planck satellite, may see this background”, Krauss added.

ASU: Researchers propose a new way to detect the elusive graviton

arXiv: Using Cosmology to Establish the Quantization of Gravity

Essential Cosmology for the Next Generation

Berkeley Center for Cosmological Physics (BCCP) and the Advanced Institute for Cosmology (IAC) “Essential Cosmology For the Next Generation” annual school promotes a high level of intellectual exchange among young scientists and seasoned, frontier science researchers and is motivated by the need for astronomers and astrophysicists to remain informed of and understand the basis of advances in many interrelated fields. Innovative, as well as efficient utilization of forthcoming large data sets require awareness of the broad science questions and latest developments. International cooperation is becoming standard and furthering this atmosphere is an important product of the conference. Perhaps most telling is the extremely positive assessment of the previous schools by the student and postdoc participants, spreading the news to the next generation of students while themselves progressing to more advanced research positions.

A range of topics in cosmology will be covered at the conference by eminent scholars in the field, with elements of both a winter school and the latest research results. Students and postdocs will present posters and give short talks. We hope that the beauty of the natural and cultural environment will act as a catalyst for young researchers to interact and generate new ideas. We encourage a diverse group of advanced graduate students, postdocs, and researchers interested in attending to apply. See the general Cosmology on the Beach website for information on the whole series since 2009.

Looking for ‘new physics’ in the Universe

Con il termine “nuova fisica” si intende un nuovo campo di ricerca che tenta di spiegare quei fenomeni della natura che i fisici non sono ancora in grado di descrivere. Oggi, sta prendendo piede sempre più l’idea in base alla quale l’Universo può essere caratterizzato da una struttura diversa rispetto a quanto previsto dagli attuali modelli o teorie. In tal senso, un gruppo di fisici hanno avviato uno studio che avrà lo scopo di aiutare gli scienziati a rendere più facile, almeno in parte, la comprensione di alcuni fenomeni della fisica fondamentale.

New physics is about searching for unknown physical phenomena not known from the current perception of the Universe. Such phenomena are inherently very difficult to detect“, explains Matin Mojaza from CP3-Origins. Together with colleagues Stanley J. Brodsky from Stanford University in the U.S. and Xing-Gang Wu from Chongqing University in China, Mojaza has now succeeding in creating a new method that can make it easier to search for new physics in the Universe (post).

The method is a so called scalesetting procedure, and it fills out some empty, but very important, holes in the theories, models and simulations, which form the basis for all particle physics today.

With this method we can eliminate much of the uncertainty in theories and models of today“, says Matin Mojaza. Many theories and models in particle physics today has the problem that they, together with their predictions, provide some parameters that scientists do not know how to set. “Physicists do not know what values they should give these parameters. For example, when we study the Standard Model and see these unknown parameters, we cannot know whether they should be interpreted as conditions that support or oppose to the Standard Model, this makes it quite difficult to study the Standard Model accurately enough to investigate its value”, explains Matin Mojaza. With the new approach researchers can now completely clean their models for the unknown parameters and thus become better at assessing whether a theory or a model holds water.

The Standard Model has for the last 50 years been the prevailing theory of how the Universe is constructed. According to this theory, 16 (17 if we include the Higgs particle) subatomic particles form the basis for everything in the Universe.

But the Standard Model is starting to fall short, so it is now necessary to look for new physics in the Universe. One of the Standard Model’s major problems is that it cannot explain gravity, and another is that it cannot explain the existence of dark matter, believed to make up 25 percent of all matter in the Universe. In addition, the properties of the newly discovered Higgs particle, as described in the Standard Model, is incompatible with a stable Universe. “A part of the Standard Model is the theory of quantum chromodynamics, and this is one of the first things, we want to review with our new method, so that we can clean it from the uncertainties“, explains Matin Mojaza. The theory of quantum chromodynamics predicts how quarks (such as protons and neutrons) and gluons (particles that keeps quarks in place inside the protons and neutrons) interact. Matin and his Chinese and American colleagues now estimate that there may be a basis for reviewing many scientific calculations to clean the results from uncertainties and thus obtain a more reliable picture of whether the results support or contradict current models and theories. “Maybe we find new indications of new physics, which we would not have exposed if we had not had this new method”, says Matin Mojaza.

He believes that the Standard Model needs to be extended so that it can explain the Higgs particle, dark matter and gravity.

One possibility in this regard is to examine the so-called technicolor theory, and another is the theory of supersymmetry. According to the supersymmetry theory, each particle has a partner somewhere in the Universe (these have not yet been found though). According to the technicolor theory there is a special techni-force that binds so-called techni-quarks, which can form other particles, perhaps this is how the Higgs particle is formed. This could explain the problems with the current model of the Higgs particle. Also Rolf-Dieter Heuer, director of CERN in Switzerland, where the famous 27 km long particle accelerator, the LHC, is situated, believes that the search for new physics is important. According to him, the Standard Model cannot be the ultimate theory, and it is only capable of describing about 35 percent of the Universe. Like CP3-Origins, also CERN has put focus on weeding out old theories and search for new physics, this happening in 2015, when the accelerator starts up again (post).

University of Southern Denmark: New groundbreaking research may expose new aspects of the Universe

arXiv: A Systematic All-Orders Method to Eliminate Renormalization-Scale and Scheme Ambiguities in PQCD

Exascale Radio Astronomy

The topics covered by the next-generation of radio telescopes will touch upon cosmology, dark ages, epoch of reionization, galaxy evolution, dark energy, dark matter, general relativity, cosmic magnetism, and pulsars etc.

Why Exascale Radio Astronomy? (PDF)