Events - Page 15

Time and place: Sep. 29, 2016 1:05 PM, Ø467

Anastasia Sokolenko, FI

In this work we propose a new interesting channel for searching new physics at the LHC. This channel is connected to the diphoton channel via electroweak gauge symmetry of the Standard Model (SM). We discuss the possibility that an apparent diphoton signal is in fact produced by the 4-photon channel, where a pair of collimated photons is misidentified as 1 photon due to finite angular resolution of the detector. In this case we expect that the gauge symmetry of the SM connects the diphoton channel to three boson channels. Also we notice that the same mechanism could give an experimental signature of $Z\rightarrow \gamma\gamma$ decay, which is theoretically forbidden by the Landau-Yang theorem. For definiteness we illustrate these ideas using one of the models that was discussed to explain the recent 750 GeV resonance, even if the later signal was not confirmed.

(The slides will be available here)

Time and place: Sep. 28, 2016 1:05 PM, Ø467

Motivated by recent experiments, we study lattices of magnetic adatoms exchange coupled to the surface of a conventional s-wave superconductor. We show that a variety of collective magnetic and electronic phases emerge in this system, due to the interplay between ferromagnetism and superconductivity. In particular, an adatom chain on a bulk (2d or 3d) superconductor can order into a magnetic spiral state leading to, and stabilized by, the opening of a topological superconducting gap within the band of YSR states induced by the adatoms. The spiral wave-vector increases sharply as the YSR energy is lowered from the quasiparticle continuum, due to a strong spin-spin exchange interaction mediated through the band of sub-gap YSR states. As the YSR band enters the topological phase, the wave-vector exhibits a peak and is thereafter driven down towards ferromagnetism due to YSR state double-exchange. We provide the range of YSR energies and adatom spacing where these phases exist for adatoms on a 3d, or 2d  superconductor. The magnetic ordering within a 2d YSR lattice is also explored.

(The slides will be available here)

Time and place: Sep. 22, 2016 5:30 PM7:00 PM, DNVA, Drammensveien 78

Professor Eric Priest, St Andrews University, Scotland:

Our Dynamic Sun

Time and place: Sep. 21, 2016 1:05 PM2:00 PM, Ø467

Oleg Lebedev, University of Helsinki

I will discuss a special role of the Higgs boson in probing the hidden sector and its connection to dark matter and inflation.

(The slides will be available here)

Time and place: Sep. 15, 2016 10:15 AM11:15 AM, Lille aud øst

Alfredo Galindo-Uribarri, Oak Ridge National Laboratory / University of Tennessee, Knoxville.

Time and place: Sep. 2, 2016 3:15 PM, Seminar Room FV414

by Octavio Palma

Time and place: Aug. 31, 2016 1:05 PM2:00 PM, Ø467

Andi Hektor, NICPB Tallinn

I will give a short introduction to Dark Matter physics. I will sum up the the main evidences of Dark Matter from the Galactic to large cosmological scales. So far the evidences are only gravitational. I will point out that even the gravitational signals of Dark Matter can hint about the deeper nature of Dark Matter, especially having soon new data from the Gaia and other soon starting experiments. Beyond gravitation, we have many experimental constraints on the ‘particle’ nature of Dark Matter and only few questionable hints of Dark Matter. Those experiments involve the accelerator (LHC at CERN), underground (‘direct detection') and cosmic experiments (‘indirect detection’). Due to rapidly evolving experimental and observational bounds the mainstream candidate of Dark Matter, Weakly Interacting Massive Particle, is losing its ground. I will point out some interesting escape scenarios of WIMP. I will conclude highlighting some interesting alternatives for WIMPy Dark Matter.

(Slides will be available here)

Time and place: July 6, 2016July 14, 2016, Crete

Conference poster and 1. Bulletin are available on the web site of theconference: 5th International Conference on New Frontiers in Physics

Time and place: June 22, 2016 1:05 PM, Ø467

Timo Hyart, University of Jyväskylä

Topological materials are characterised by the existence of momentum space topological defects, topological invariants and protected surface states. After the classification of the possible fully gapped topological phases, the attention has now turned to the possible momentum space topological defects appearing in gapless semimetals and nodal superconductors. In this talk I will give an overview of the gapless topological phases containing Weyl points (monopoles) and Dirac lines (vortex lines) in the momentum space. The next step in the increasing complexity of the momentum space topological defects is to consider the topology of the systems containing multiple Dirac lines. I will describe how the structural symmetries of the systems can allow stabilising a momentum-space topological defect where several Dirac lines meet and merge in the momentum space forming a momentum-space equivalent of the real space nexus considered before for Helium-3. By the bulk-boundary  correspondence of topological media the presence of Dirac lines leads to formation surface states. I will discuss the properties of these surface states in a nexus semimetal.

(The slides will be available after the talk)

Time and place: June 16, 2016 9:15 AMJune 17, 2016 5:15 PM, Lille Fysiske Auditorium (FV232), Physics Building, UiO

On June 16th and 17th, the second seminar for the Strategic Research Intitiative EarthFlows will be arranged at UiO.

Time: June 15, 2016June 28, 2016

The 2016 CERN-JINR European School of High-Energy Physics will take place in Skeikampen (close to Lillehammer), Norway, 15 - 28 June 2016.

Time and place: June 3, 2016 3:15 PM, Seminar Room V414

The next PGP-AMKS Poster Seminar is on 3 June! Are you also curious to know what research is brewing on the other side of the hall in PGP-AMKS group? Please join us to listen to short talks by our new colleagues, and to look at some posters!

Time and place: May 27, 2016 3:15 PM, Seminar Room FV414

Truls Norby from the Department of Chemistry (UiO) will talk about the SEALEM project.

Time and place: May 20, 2016 10:15 AM4:00 PM,

Trial lecture: Pattern formation in granular materials (10:15)

Dissertation: Statistical properties of sheared suspensions (13:15)

Time and place: May 18, 2016 1:05 PM2:00 PM, Ø467

Håvard Tveit Ihle, ITA

There is a growing interest in how the particle nature of dark matter (DM) can affect cosmological and astrophysical observables. Kinetic decoupling of DM from the heat bath in the early universe, e.g., leads to a pronounced cutoff in the matter power spectrum. Traditional WIMP models for DM (like SUSY) typically result in MeV-scale kinetic decoupling, corresponding to a cutoff at unobservably small scales. Here, we provide instead a classification of DM models that result in keV-scale kinetic decoupling. Such models result in a potentially observable cutoff in the power spectrum, at the scale of dwarf-galaxies and hence possibly addressing the missing satellite problem. The main focus of the talk will be on the decoupling process of DM in the early universe, implications for model building, and some examples from our work.

(The slides are now available)

Time and place: May 11, 2016 3:30 PM4:30 PM, Ø467

Robert Wagner, University of Stockholm

The past decade has seen a dramatic improvement in the quality of data available at high-energy gamma-rays. The all-sky LAT instrument on board of the Fermi satellite has revealed about 2,000 sources in the sky at the 100 MeV – 100 GeV band, and almost 200 sources have been detected at even higher energies, E>100 GeV, gamma rays energies by pointed, ground-based Imaging Air Cherenkov Telescopes.

These so-called very high-energy (VHE) gamma rays gamma rays cannot be produced in thermal processes, but are produced by interactions of high-energy particles. Gamma rays thus trace populations of such particles and enable the cosmic particle accelerators to be imaged and studied. Gamma-ray emitting particle accelerators are ubiquitous in the Galaxy and beyond; they include a variety of galactic and extragalactic objects. Details of the acceleration mechanisms as well as the role high-energy particles play in the evolution of star forming systems and galaxies remain to be fully understood. Gamma-rays can also be used as probes of the physics of the early universe, of fundamental physics, and could be products of dark matter annihilation in some cold dark matter realizations.

... (continued below)

(The slides will be available after the talk)

Time and place: May 4, 2016 1:15 PM, Ø467

Bjørn Solheim, FI

What do space and time look like on the very smallest scales ?  Do space and time really exist, or are they just emergent concepts that serve as useful approximations in some physical domains? Following Einstein's insights we are lead to believe that the answers to questions about microscopic geometry lie in finding a microscopic theory of gravity. Loop quantum gravity (LQG) is  a theory that encapsulates the core principles of quantum theory and general relativity (GR) with minimal extra assumptions. LQG can be seen both as a specific quantization of GR, and as a set of general methods for non-perturbative  quantization of diffeomorphism invariant theories in a background independent manner. LQG leads to a well-defined theory of (spatial) quantum geometry, where geometric variables like area and volume take discrete values. LQG has been "successfully" applied to cosmology and black holes where it eliminates the singularities and gives a fully quantum version of these gravitational systems. The presentation will focus on the foundations of LQG with some applications in cosmology.

(The slides are now available)

Time and place: Apr. 29, 2016 3:15 PM, Seminar Room V414

by Vera Schlindwein (Alfred Wegner Institute, Bremen).

Time and place: Apr. 27, 2016 1:05 PM2:00 PM, Ø467

Felix Kahlhoefer, DESY (Hamburg)

I will discuss the motivation, the advantages and the problems of using simplified models as a tool to interpret LHC searches for dark matter. I will present a few examples for how this approach can be used to understand the complementarity of different dark matter search strategies. Finally, I will focus on various consistency conditions that should be imposed even on the most simplified models. These conditions can imply the presence of additional new particles and interactions that may change the phenomenology of the model in important ways.

(The slides are now available)

Time and place: Apr. 15, 2016 3:15 PM, Seminar Room V414

by Harald Throne-Holst from National Institute for Consumer Research (SIFO).

Time and place: Apr. 13, 2016 1:05 PM, Ø467

Anders Tranberg, University of Stavanger

The asymmetry between matter and antimatter is still an unsolved mystery of astroparticle physics. Presumably, the asymmetry was generated during a strong phase transition at or before the electroweak symmetry breaking transition in the Early Universe. Electroweak baryogenesis as a scenario has a long and illustrious history of trial and not-quite-success. I will present a related, competing model ("Cold" electroweak baryogenesis), and demonstrate how one may numerically compute and actual number for the generated asymmetry from first principles.

(The slides are now available)

Time and place: Apr. 1, 2016 3:15 PM, Seminar Room V414

Sebastian Westermann from the Department of Geosciences (UiO) will talk about:

Permafrost in a Changing Climate

Time and place: Apr. 1, 2016 10:15 AM4:00 PM,

Trial lecture: Electromagnetic methods for monitoring of CO2 sequestration (10:15)

Dissertation: Advances in 3D finite-difference modelling of electromagnetic fields in the conductive Earth (13:15)

Time and place: Mar. 30, 2016 1:05 PM, Ø467

Parampreet Walia, FI

Advancements in experiments for unveiling the nature of Dark Matter (DM) call for more accurate predictions from theorists. Thus a lot of recent interest has developed in calculating higher order corrections to DM annihilation and scattering processes.

Typical Majorana WIMP annihilation to fermions is helicity suppressed. But emission of an extra gauge boson can lift this suppression. Electroweak bremsstrahlung has been studied in much detail earlier, but surprisingly not equal attention has been given to gluon bremsstrahlung.

The major difference between the two cases comes from the fact that quarks and gluons fragment to form hadrons.  Computing the spectrum from model to model basis is computationally expensive. I will present a computation friendly approach, which agrees with the real spectrum to a very high accuracy. And then in the end, I would also discuss the impact of QCD corrections on relic density calculations.

(The slides are now available)

Time and place: Mar. 16, 2016 1:05 PMMar. 17, 2016 2:00 PM, Ø467

Riccardo Catena, Chalmers (Göteborg)

About five-sixths of all matter in the Universe remain hidden from our view and behave like a dissipation-less fluid called dark matter. The experimental technique known as direct detection (DD) will play a pivotal role in shedding light on the nature of dark matter during the next decade. It searches for nuclear recoil events induced by the non-relativistic scattering of Milky Way dark matter particles in low-background detectors. An effective theory approach is a solid strategy to interpret DD experiments when the momentum transferred in the dark matter scattering by nuclei is small compared to the mass of the particle mediating the interaction. In this talk I compare a recently developed non-relativistic effective theory for dark matter-nucleon interactions to current DD data, including the observation of a modulation signal in the nuclear recoil energy spectrum reported by the DAMA collaboration. Emphasis will be placed on the strength of the proposed effective theory approach and on how it compares to the standard paradigm for DD.

(The slides are now available)

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