Events - Page 26

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)

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)

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)

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)

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)

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)

Abram Michael Beauregard Krislock, FI

Go effectively models physics itself: The game has an enormous amount of complexity and is full of beautiful and mind-boggling phenomena. In spite of this, there are only a small number of rules to the game. A study of go can help one with pattern recognition, logical determinism, strategic planning, and concentration. As physicists are becoming more and more proficient in using sophisticated statistics and computer science for their studies, they may be inspired by an ultra recent advancement in computer learning: For the first time, a computer has beaten a professional player in go. Last but not least, go is a ton of fun.

(Slides will be available after the talk)

Ivica Picek, university of Zagreb

Besides being a first indication for the second scalar particle, a recent hint for the 750 GeV resonance at the LHC  requires additional particles such as those employed in models of radiative neutrino mass generation. The scalar triplet realizations seem to be preferable with respect to the 2HDM benchmark and provide in the inert variant the dark matter candidates.

(The slides are now available)

Andrzej Hryczuk, FI

The thermal relic abundance of the dark matter is now determined observationally to a per cent level accuracy. It is also an increasingly useful tool to exclude, constrain or motivate models beyond the Standard Model of particle physics. It comes then with no surprise that in the recent years a considerable effort has been made to revise and improve some of the aspects of thermal relic density calculations. In this talk I will concentrate on the important physics concepts used in such calculations, highlighting some less commonly discussed details. Towards the end I will show some recent results, serving as examples of the relevance of the effects studied.

(The slides are now available)

Chad Finley, Oskar Klein Centre (Stockholm)

The IceCube Neutrino Observatory lies two kilometers deep within the ice at the South Pole, Antarctica.  With one cubic kilometer of instrumented volume, IceCube enables the study of a wide range of phenomena: neutrino astronomy, dark matter searches, neutrino oscillations, and cosmic ray physics.  Recently IceCube has announced the long-awaited discovery of high energy neutrinos from deep space.  These neutrino energies are approximately 100 million times greater than the energies of neutrinos previously observed from the sun and supernovae. I will review IceCube's latest results with particular attention to this new flux. I will also discuss what we hope to measure in the near future with IceCube and the next generation of neutrino telescopes.

(The Slides are now available)

Stefan Hofmann, LMU Munich

A relativistic framework for describing black-hole interiors as bound states of a large number of quantum constituents will be presented. The macroscopic and microscopic description can be linked via a simple scaling law relating the black-hole mass to the number of black-hole constituents.

(The slides will be available after the talk).

Piero Ullio, SISSA (Trieste)

The dark matter puzzle is one of deepest and longest-standing problems in Science. While there is overwhelming evidence that dark matter is the building block of all structures in the Universe, its nature remains unknown.

There are several theoretical frameworks predicting that dark matter halos - including the halo of our own galaxy - are made of particles which can annihilate in pairs or decay into ordinary Standard Model states, giving rise to exotic astrophysical signals.

The focus in recent years has been in particular on the search for exotic components with gamma- and cosmic-ray observatories, with a dramatic improvement in quality and coverage of the available data. 

Unfortunately, for none of the originally proposed targets a dark matter signal stands clearly above backgrounds from standard astrophysical sources: it is then apparent that to keep exploiting these channels as efficient tools to either discover dark matter or set constraints on dark matter candidates, a closer addressing of signals and backgrounds are needed. 

We illustrate this point for two targets, the Galactic center and dwarfs satellites which most recently have been highlighted, respectively, as most promising for a tentative detection and most constraining on particle dark matter models.

Björn Herrmann, LAPTh (Annecy)

A powerful tool to constrain a new physics model is to predict the relic density of dark matter and compare it to the recent limits published by Planck in order to identify (dis)favoured regions of parameter space. After reviewing the standard calculation of the dark matter relic density in the freeze-out picture, I will discuss several uncertainties entering this calculation. Focusing then on the particle physics aspects, I will consider the case of the Minimal Supersymmetric Standard Model and present the project DM@NLO, which aims at improving the preciction of the neutralino relic density by including radiative corrections to the (co)annihilation cross-section of the dark matter candidate. In particular, I will show that the impact of these corrections can be numerically larger than the current experimental uncertainty on cosmological data.

(The slides are now available).

Joachim Kopp, University of Mainz

We consider two scenarios in which the first experimental hint for the particle physics nature of dark matter (DM) comes from highly boosted DM particles. The first scenario interprets the high energy events observed in IceCube as a signal of PeV DM decaying to a much lighter state, which in turn is detected in IceCube. The model explains the event rate and spectrum observed in IceCube, it shows a preference for shower-like events at the highest energies, and it features a small dip in the spectrum at few hundred TeV.  The second scenario is a very generic dark photon model. We point out that DM production at the LHC can be accompanied by final state radiation in the form of "dark photons", which decay back to SM particles.  We discuss this process analytically and numerically in analogy to collinear particle showers in QED and QCD. The smoking gun signal of this "radiating DM" scenario are collimated jets or lepton jets with unusual properties.

(The slides are now available.)

Bryan Webber, University of Cambridge

Tests of the Standard Model and searches for new phenomena at the Large Hadron Collider depend heavily on computer simulations of signal and background processes.  Monte Carlo event generators aim to simulate the final states of high-energy collisions in full detail, down to the level of individual stable particles.   The talk will review the physics behind these programs, their main ingredients and theoretical status, with emphasis on recent work to improve their precision.  Comparisons with the latest LHC data will illustrate these developments, and the places where further improvements are needed.

(The Slides are now available)

Gabrijela Zaharijas, University of Nova Gorica

The Isotropic Gamma-ray Background (IGRB) up to 820 GeV has been recently measured by the Fermi LAT using 50 months of data. Understanding the origin of this IGRB is a crucial task that requires to identify and model possible contributions in detail. Dark matter annihilation signals integrated over all cosmic epochs have been proposed to account for a portion of the measured IGRB intensity. I will discuss the theoretical predictions for the clustering of dark matter signal and refined predictions for the contribution of the unresolved astrophysical source populations to the IGRB. We use these ingredients to set the limits on the dark matter annihilation cross section which turn out to be comparable to the ones set by the observation of dwarf spheroidal galaxies and Milky Way halo for sub-TeV dark matter masses, while they improve upon them at the high mass end due to the significant energy extension of the isotropic measurement. In addition I will  compare these finding with complementary techniques which probe the cosmological dark matter annihilations, as those of the small scale angular anisotropies and gamma ray cross correlations with galaxy catalogs.

(Slides are now available)

David Mota, ITA

Several extensions of the standard cosmological model include scalar fields as new degrees of freedom in the underlying gravitational theory. A particular class of these scalar field theories include screening mechanisms intended to hide the scalar field below observational limits in the solar system, but not on galactic scales, where data still gives freedom to find possible signatures of their presence.  I describe how one can use structure formation to study screening mechanisms in extensions to General Relativity. In particular, I will present observable signatures of modified gravity in the nonlinear matter power spectrum, on the halo mass function and other properties of galaxy clusters. Those would help us to discriminate between models with and without scalar fields and even between different screening mechanisms.

(The slides are now available)

Dr. Terry Onsager, National Oceanic and Atmospheric Administration, USA/Space Weather Prediction Center, USA.

Kåre Olaussen, NTNU Trondheim

After 100 years people are still trying to modify (or mutilate) the Einstein General Theory of Relativity. I will first give a general overview of various possibilities, as I learned at a workshop this summer.

Next I will discuss in more detail the possibility of a non-minimal coupling of Einstein gravity to scalar fields, and some modest computations I have done with a master student on that model (in the Robertson-Walker geometry).

The presentation will mainly be aimed at an audience with limited experience with general relativity.

(Slides will be available after the talk).

Ipsita Mandal, Perimeter institute

We devise a renormalization group analysis for quantum field theories with Fermi surface to study scaling behaviour of non-Fermi liquid states in a controlled approximation. The non-Fermi liquid fixed points are identified from a Fermi surface in (m+1) spatial dimensions, while the co-dimension of Fermi surface is also extended to a generic value. We also study superconducting instability in such systems as a function of dimension and co-dimension of the Fermi surface. The key point in this whole analysis is that unlike in relativistic QFT, the Fermi momentum k_F enters as a dimensionful parameter, thus modifying the naive scaling arguments. The effective coupling constants are found to be combinations of the original coupling constants and k_F.

The slides are now available.

Tomás Gonzalo, University College London

Grand Unified Theories are a very well motivated extension of the Standard Model, but the landscape of models and possibilities is overwhelming, and different patterns present rather distinct and unique phenomenology. We present in this work a way to automatise the model building process, by considering a top-bottom approach that constructs viable and sensible theories from a small and controllable set of inputs at the high scale. By providing a GUT scale symmetry group and the field content, all the possible symmetry breaking paths are generated and checked for consistency, ensuring anomaly cancellation and Standard Model embedding. We emphasise the usefulness of this process for various models such as a Supersymmetric SO(10) model, a non-SUSY left-right symmetry model or a theory of GUT inflation. 

(Slides are now available).

The conference aims to promote scientific exchange and the development of novel ideas, with a particular emphasis on interdisciplinarity.

Yong Tang, KIAS

This talk will discuss some possible connections between neutrinos and dark matter, in light of astrophysical observations. Contents include self-interacting dark matter, sterile neutrinos and IceCube Events. 

The slides are now available.