Archivi tag: modified gravity

Hot Topics in General Relativity and Gravitation

In this centennial anniversary of General Relativity, we will hold a conference on Hot Topics in General Relativity and Gravitation with the motivation to emphasize the tremendous progresses that have been made in Astrophysics and in Cosmology since Einstein’s discovery of General Relativity (GR) in 1915. This international conference will be held at ICISE as part of the Rencontres du Vietnam. Continua a leggere Hot Topics in General Relativity and Gravitation

Annunci

Dark Side of the Universe 2014

The theme of this years’ meeting is Surveying the Dark Side of the Universe – Theory and Observations. Continua a leggere Dark Side of the Universe 2014

2014 Higgs Symposium: New Horizons in Particle Cosmology

The Standard Model of Cosmology is now on a solid observational foundation. But the empirical success of the model forces us to consider its outstanding fundamental problems: What drives the current expansion of the Universe to accelerate? Did a period of Cosmological Inflation set the initial conditions for the observable Universe? What is the nature of the Dark Matter which molds the formation of structure and how is it connected to Particle Physics? Is Einstein’s Theory of Gravity correct on all scales or will we have to modify it on cosmological scales? Continua a leggere 2014 Higgs Symposium: New Horizons in Particle Cosmology

Rencontres de Moriond on Cosmology

The Rencontres de Moriond session on Cosmology will review the subject 2 years after the last edition.

The main topics of the conference are:

  • CMB anisotropies
  • Reionization
  • Dark energy probes
  • Dark Matter
  • Inflation
  • Modified gravity
  • Massive gravity
  • Galaxy clusters
  • SZ
  • Non gaussianities

The conference will include both review and contributed talks and will be organized only in plenary sessions

27° Texas Symposium on Relativistic Astrophysics

The 27th Texas Symposium on Relativistic Astrophysics will be held in downtown Dallas December 8 – 13, 2013. It is organized by the Department of Physics at The University of Texas at Dallas (UTD) and is chaired by Wolfgang Rindler and Mustapha Ishak. The Symposium will include both invited and contributed talks and posters. This will be a special and historically meaningful Jubilee meeting, marking the 50th anniversary, almost to the day, of the very first of these Texas Symposia, held in Dallas in December 1963. We are excited to welcome hundreds of international astrophysicists back to Dallas fifty years later, both to celebrate the past 50 years of Texas Symposia and relativistic astrophysics and to kick off the next 50 years of remarkable discoveries.

The Symposium will cover the following topics:

Cosmology

  • Cosmic acceleration/dark energy
  • Cosmic microwave background
  • Early universe (Inflation, Cyclic Model, CCC cosmology …)
  • Galaxy formation and reionization
  • Inhomogeneous cosmologies, averaging, and backreaction
  • Large-scale surveys
  • Quantum gravity/cosmology and string cosmology
  • Weak gravitational lensing
  • Experimental/observational cosmology – other topics
  • Theoretical cosmology – other topics
Compact objects and galactic/cluster scales
  • Black holes, mergers, and accretion discs
  • Galaxy evolution and supermassive black holes
  • Imaging black holes
  • Microlensing and exoplanets
  • Neutron stars, pulsars, magnetars, and white dwarfs
  • Nuclear Equation of State for Compact Objects
  • Singularities
  • Strong gravitational lensing
  • Supermassive black hole binaries
  • Tidal disruption of stars by supermassive black holes
  • Compact object observations – other topics
  • Compact object theory – other topics
High-energy astrophysics and astroparticle physics
  • Active galactic nuclei and jets
  • Cosmological implications of the Higgs and the LHC
  • Dark matter astrophysics
  • Dark matter experiments and data
  • Gamma-ray bursts, SNe connection, and sources
  • High-energy cosmic rays (VHE, UHE, mechanisms, etc.)
  • High-energy gamma-rays
  • Nuclear Astrophysics
  • Supernovae and their remnants
  • High-energy astrophysics/astroparticle physics – other topics
Testing general relativity and modified gravity
  • Alternative theories of gravity
  • Strong-field tests of general relativity
  • Testing general relativity at cosmological scales
  • Testing general relativity – other topics
  • Modified gravity – other topics
Gravitational waves
  • Electromagnetic counterparts of gravitational wave sources
  • Ongoing and planned gravitational wave experiments
  • Gravitational wave theory and simulations
  • Results and progress from gravitational wave searches
  • Supernovae and Gravitational Wave Emission
  • Gravitational waves – other topics
Numerical relativity
  • Computer algebra and symbolic programming
  • Locating black hole horizons
  • Numerical simulations
  • Relativistic magnetohydrodynamics
  • Numerical relativity – other topics
Other ongoing and future experiments and surveys
  • ACT, AMS, BOSS, CFHT, Chandra, DES, Euclid, Fermi, HETDEX, HSC, JWST,
  • LHC, LSST, NuSTAR, Pan-STARRS, Planck, SDSS, SKA, SPT, WFIRST, WMAP, …
  • (to be completed after abstract submissions)
And also:
History of relativistic astrophysics
History of the Texas Symposium and interface with other anniversaries
The Kerr solution – 50 years later

Cosmology in the Planck Era

The Rencontres du Vietnam on Cosmology in the Planck Era will review the most recent status of the field. The conference will consist of plenary sessions for invited indepth oral presentations (review talks and talks on specific specialised topics), and contributed papers, in the form of relatively short oral papers (sollicitated or selected from abstract submission). Special emphasis is being placed on active participation by young researchers and post-docs.

The main topics of the conference are:

  • Planck Cosmology Results
  • Cosmology with wide-field SZ cluster surveys
  • Polarization
  • Supernovae
  • BAO
  • Inflation
  • Modified Gravity
  • Dark matter candidates
  • Dark matter searches

Did the Milky Way and Andromeda already collide?

Gli scienziati ritengono che tra circa 3 miliardi di anni la Via Lattea si scontrerà con Andromeda e che tale evento sarà il primo di una serie di collisioni galattiche. Oggi, però, un gruppo di astronomi guidati da Hongsheng Zhao della University of St Andrews propone un nuovo scenario in cui viene ipotizzato che le due galassie si sono già scontrate una volta, circa 10 miliardi di anni fa, e che la nostra conoscenze sulla gravità sono fondamentalmente errate. In realtà, questa idea potrebbe spiegare non solo la struttura della nostra galassia e quella di Andromeda ma anche la presenza delle galassie satelliti.

The Milky Way, made up of about 200 billion stars, is part of a group of galaxies called the Local Group. Astrophysicists often theorise that most of the mass of the Local Group is invisible, made of so-called dark matter. Most cosmologists believe that across the whole Universe, this matter outweighs ‘normal’ matter by a factor of five.

The dark matter in both Andromeda and the Milky Way then makes the gravitational pull between the two galaxies strong enough to overcome the expansion of the cosmos, so that they are now moving towards each other at around 100 km per second, heading for a collision 3 billion years in the future.

But this model is based on the conventional model of gravity devised by Newton and modified by Einstein a century ago, and it struggles to explain some properties of the galaxies we see around us. Zhao and his team argue that at present the only way to successfully predict the total gravitational pull of any galaxy or small galaxy group, before measuring the motion of stars and gas in it, is to make use of a model first proposed by Prof. Mordehai Milgrom of the Weizmann Institute in Israel in 1983. This modified gravity theory (Modified Newtonian Dynamics or MOND) describes how gravity behaves differently on the largest scales, diverging from the predictions made by Newton and Einstein.

Zhao and his colleagues have for the first time used this theory to calculate the motion of Local Group galaxies. Their work suggests that the Milky Way and Andromeda galaxies had a close encounter about 10 billion years ago.

If gravity conforms to the conventional model on the largest scales then taking into account the supposed additional pull of dark matter, the two galaxies would have merged. “Dark matter would work like honey: in a close encounter, the Milky Way and Andromeda would get stuck together, figuratively speaking“, says team member Prof. Pavel Kroupa from Bonn University. “But if Milgrom’s theory is right“, says his colleague Benoit Famaey (Observatoire Astronomique de Strasbourg), “then there are no dark particles and the two large galaxies could have simply passed each other thereby drawing matter from each other into long thin tidal arms“. New little galaxies would then form in these arms, a process often observed in the present-day Universe. Zhao explains: “The only way to explain how the two galaxies could come close to each other without merging is if dark matter isn’t there. Observational evidence for a past close encounter would then strongly support the Milgromian theory of gravity”. Just such a signature might already have been found. Astronomers struggle to account for the distribution of dwarf galaxies in orbit around both the Milky Way and Andromeda.

The dwarf galaxies could be explained if they were born from gas and stars ripped out of the two parent galaxies during their close encounter. Pavel Kroupa sees this as the ‘smoking gun’ for the collision.

Given the arrangement and motion of the dwarf galaxies, I can’t see how any other explanation works”, he comments. The team now plan to model the encounter using Milgromian dynamics and are developing a computer code at Bonn University for this purpose. In the new model, the Milky Way and Andromeda are still going to crash into each other again in the next few billion years, but it will feel like ‘deja vu’. And the team believes that their discovery has profound consequences for our current understanding of the Universe. Pavel Kroupa concludes, “If we are right, the history of the cosmos will have to be rewritten from scratch”.

RAS: Did Andromeda crash into the Milky Way 10 billion years ago?
arXiv: Local Group timing in Milgromian dynamics. A past Milky Way-Andromeda encounter at z>0.8

20th International Conference on General Relativity and Gravitation (GR20) and the 10th Amaldi Conference on Gravitational Waves (Amaldi10)

The 20th  International Conference on General Relativity and Gravitation (GR20)  and the 10th Amaldi Conference on Gravitational Waves (Amaldi10) will  take place from 7th – 13th July 2013 at Uniwersytet Warszawski, Warsaw, Poland. GR20  is the latest in the series of triennial international conferences held under the auspices of the International Society on General Relativity and Gravitation. This conference series constitutes the principal international meetings for scientists working in all the areas of relativity and gravitation. The Amaldi conferences are held under the auspices of the Gravitational Wave International Committee. Since 1997, they have been held every two years and are regarded as the most important international conferences for the gravitational wave detection community. This time, in Warsaw,   GR20  and Amaldi10 are organized as a joint event.

The program of the conference, among many topics,  includes:  Planck Results,  Dark Energy,  Formation of the Trapped Surfaces, Dynamics of Asymptotically AdS spacetimes,  Gravity and Condensed Matter Correspondence,  Numerical Relativity and Its Applications to Astrophysics and High Energy Physics, Neutron Stars, Formation of Supermassive Black Holes, Modified Gravity as Alternatives to Dark Energy or Dark Matter,  Cold Atoms for Equivalence Principle Tests and GW Detection, Quantum Fields in Curved Space-time, Higher-Dimensional Spacetimes, Loop Quantum Gravity, Strings and Branes.