The accepted wisdom is that a large fraction of our Universe is comprised of particle dark matter. Modified models of gravity have been studied for a long time, but the notion of emergent spacetime has given this approach a new direction. Verlinde’s emergent gravity (EG) proposal has revived the discussion, and since last November there have several works in the literature testing this new scenario.
Neutrinos are the most elusive particles of the Standard Model (SM) of particle physics. They can be produced in a number of reactions, such as natural radioactivity in the earth (geo-neutrinos), nuclear fission in reactors (reactor neutrinos), supernova explosions (supernova neutrinos), and fusion processes in the Sun (solar neutrinos).
A galaxy rotation curve is a plot of the orbital velocities of stars or gas in the observed galaxy versus the radial distance from the galaxy's center. What turns out is that galaxies in our universe seem to achieve too high velocities, such that the gravity generated by the observable matter (stars, gas) could not hold them together. This has led scientists to believe that there is some extra matter, not visible, that generates the extra gravity that galaxies need to stay intact. This extra matter is what we call dark matter, one of the most fascinating problems in physics nowadays. Unlike normal matter, dark matter does not interact with the electromagnetic force; therefore it does not absorb, emit or reflect light and because of this it is very hard to detect. It is possible that it interacts through gravity and weak force (WIMPs-weakly interacting massive particles), but it is also possible that it interacts only through gravity, which would make it even harder to spot.
The first combined search for neutrino point sources has been performed by the ANTARES and IceCube collaborations. The result of this joint analysis has been submitted to the Astrophysical Journal as well as to the ArXiv (hep-ex/1511.02149v1). No source has been identified, but the complementarity of the two experiments improves the sensitivity to point sources, thus allowing for more stringent upper limits on the neutrino flux from the sources considered in the analysis.
The Cosmic Neutrino Background (CNB) is a solid prediction of the Standard Models of Particle Physics and Cosmology. In the early universe, neutrinos were formed as part of the thermal bath, a hot plasma filling the universe (thermal production). As the universe expanded and cooled down to MeV temperatures, the neutrinos decoupled from the thermal bath, traveling freely through space ever since. Neutrinos are very weakly interacting particles, which makes the detection of this neutrino background very challenging and so far experimentally inaccessible. However, on the other hand, this same property implies that once we succeed in measuring the cosmic neutrino background, we can not only learn something about the properties of neutrinos but also the CNB is a window to the very early universe, back to the times of the formation of light elements in Big Bang Nucleosynthesis (BBN), when the neutrinos decoupled from the thermal bath at about two minutes after the “Big Bang”. For comparison, the cousin of the CNB, the better-known Cosmic Microwave Background (CMB), consisting of background photons instead of neutrinos, had lead to major breakthroughs in modern cosmology. This window however only leads back to temperature around 1 eV, nearly 400,000 years later than the CNB window. This paper discusses how physics beyond the standard model, in particular non-thermally generated right-handed neutrinos, can modify the CNB predictions.
Alicia Rivera (El Pais), interviews Fabiola Gianotti, future Director General at CERN, on her professional career, the discovery of the Higgs boson, gender balance in Science and her musical expertise as a pianist.
Article published in El País on 21 june 2015.
Alicia Rivera reports on Invisibles15, particularly outlining synergies between Science and Art. Exploring those connections is the aim of the outreach sessions organised in collaboration with the Thyssen Bornemisza Museum.
Indirect searches for dark matter through γ-rays are among the most promising ways to unravel the nature of this mysterious component of the Universe. Here we discuss a recent analysis performed by the Fermi-LAT collaboration focused on observations of dwarf galaxies.
Did the early Universe undergo inflation, a period of extremely rapid, almost exponential, expansion? Since its development in the 1980s, the idea of inflation has been very appealing from a theoretical viewpoint, although solid observational evidence was still to be found. Recently, the Planck satellite released its full survey data, shedding some light on the question.
The axion – a hypothetical light elementary particle – is among the most promising extensions of the Standard Model of particle physics. Not only does it solve a long-standing problem within the Standard Model, the strong CP problem, but it could also be the source of dark matter, a mysterious substance five times more abundant than the ordinary 'visible' matter in our Universe. This paper reports on recent results and future plans for the search of this particle. If they exist, axions should be produced abundantly in the sun and can be searched for with special telescopes such as CAST and IAXO.
Neutrino oscillations have been confirmed in many experiments in the last two decades. Almost all the observed oscillations fit quite well in the standard three neutrino picture where we have electron, tau and muon ”type or flavour” neutrinos. Oscillations can occur as the flavour of the neutrino does not correspond to a distinct massive particle. The distinct mass-state neutrinos are the physical particles that move freely through space and are made up of a combination of electron, tau and muon flavour neutrinos. So if you observe a neutrino in flight, you might observe the muon component one time, and the electron component the next. It is this change of neutrino flavour over time that we call neutrino oscillations.
One of the most exciting news of this year was the recent claim from the BICEP2 experiment of an indirect measurement of primordial gravitational waves. The experiment is based in the South Pole and designed to measure the polarization of the cosmic background radiation, focusing on the so-called B-modes. These modes can give insight on the physics of early stages of the Universe. In particular, inflationary theories predict the existence of a gravitational wave background which in turn can be seen nowadays as B-modes of polarized cosmic radiation. Unfortunately, there are other sources of B-modes, such as synchrotron radiation, gravitational lensing or polarized thermal emission from diffuse galactic dust.
The Fermi-LAT Space Telescope looks deeply inside the high energy cosmos providing a detailed picture of the Universe's most extraordinary phenomena. Among its powerful discoveries (blazars, active galaxies, gamma-ray bursts, neutron stars and even high energy eruptions from our own Sun) the most surprising and challenging one is an excess in gamma-rays coming from the center of our Galaxy, that cannot be explained with the standard astrophysical background. What are these unexpected high energy messengers telling us?
Below you will find a recently published article about Invisibles. The article discusses the general topics of dark matter, dark energy and neutrinos, and the European efforts to research them.
It also highlights the training nature of the network, which provides next generation scientists with the necessary skills to lead this quest for knowledge.