AstroParticle Physics

Astroparticle Colloquium History
Date	Room	Speaker	Title
Oct 15 2013 14:00	SISSA, Room 005	C.J. Fewster (University of York, U.K.)	On preferred states and the Hadamard condition
ABSTRACT: The vacuum state of Minkowski space quantum field theory is distinguished as a state of maximal symmetry. \r\nGeneral curved spacetimes have no nontrivial symmetry and therefore lack an obvious candidate vacuum state.\r\nNonetheless, one might wonder whether there is still a way of selecting a preferred state. I will discuss various aspects of this issue, describing a general no-go theorem that excludes the existence of a local and covariant choice of preferred state and also a recent paper of Afshordi, Aslanbeigi and Sorkin [arXiv:1205.1296] which gives a prescription for a covariant, nonlocal, preferred \"SJ state\" of the free scalar field. I will give some positive results concerning SJ states but will show, on the other hand, that they fail to be Hadamard in general and have other undesirable properties that render them physically unsatisfactory. Ialso describe further results that \r\nstrengthen the physical motivation underlying the Hadamard condition.
Sep 05 2013 11:00	SISSA - Room 135	Martin Bojowald (Penn State)	Effective space-time in loop quantum gravity and signature change
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May 21 2013 14:00	Room 005	Sergio Palomares Ruiz (IST, Lisbon)	Seeing dark matter through neutrino eyes
ABSTRACT: In this talk I will discuss the different ways to use neutrinos as tools for dark matter detection. The annihilation or decay of dark matter particles in regions of high density, as the Galactic center, or after being captured in the Sun or the Earth provides us with the possibility to constrain different dark matter properties. Whereas in the first case limits on the annihilation cross section can be obtained, with neutrinos from annihilations in the Sun or Earth we can set constraints on the elastic scattering cross section of dark matter off nucleons, the same quantity the direct search experiments are sensitive to. I will discuss current and future limits and perspectives for a very large mass range, from MeV to TeV, by using different neutrino experiments, such as IceCube or Super-Kamiokande. I will also mention the main uncertainties involved in these searches.
May 07 2013 14:00	Sissa - Room 005	Diego Blas (CERN)	Aspects of Lorentz violation in cosmology
ABSTRACT: Recent approaches to quantum gravity question the role of Lorentz invariance as a fundamental symmetry of nature. This has several implications for cosmology, both at the fundamental and at the observational level. At the fundamental level it allows for new ideas for dark energy or dark matter. At the observational level, it predicts deviations from the standard ΛCDM paradigm at the level of perturbations. These can be tested very accurately with current data from CMB and large scale structure. In my talk I'll elaborate on the previous aspects.
Mar 27 2013 16:00	Room 005	Kostas Skenderis (University of Southampton)	A holographic view of the very early universe
ABSTRACT: In this talk I will give an overview of holographic cosmology. I will first discuss standard inflation, show that it is holographic and discuss the new insights that come from this. I will then present new holographic models that describe a universe that was non-geometric at early times and describe the phenomenology and the observational signatures of these models.
Mar 25 2013 16:00	Room 135	John Donoghue (University of Massachussets)	The effective field theory of quantum general relativity
ABSTRACT: Effective field theory techniques allow the extraction of reliable quantum predictions of General Relativity at low energy. I will describe the effective field theory treatment for gravitational physics, and show how one finds the quantum correction to the Newtonian potential.
Feb 06 2013 16:00	Room 135	Aaron Vincent (IFIC, Valencia)	Dark Matter and other exotic sources: possible origins of the galactic 511 keV positron signal
ABSTRACT: Observations tell us that 10^43 positrons are annihilating every second in the Milky Way, corresponding to the creation and subsequent destruction of a staggering 3 solar masses of antimatter over the lifetime of the Galaxy. The most up-to-date observations of the 511 keV annihilation line come from the INTEGRAL/SPI satellite, which has mapped this signal to unprecedented accuracy. I will give an overview of what can be learned from the spectrum, intensity and morphology 511 keV sky --- which is uncorrelated with any other signal in the EM spectrum --- including some developments in the field from the past year. A plethora of possible sources exist, but most cannot explain the large central bulge component of the observed signal. I will present some recent work which has focused on solving this 40 year-old mystery, including the effect of positrons from extragalactic sources, as well as a possible dark matter origin through decaying, annihilating or more exotic models, such as eXciting Dark Matter (XDM).
Dec 18 2012 16:00	Room 005	Marco Cavaglia (University of Mississippi)	LIGO: The Laser Interferometer Gravitational-wave Observatory
ABSTRACT: Gravitational waves are distortions of the space-time geometry that propagate with the speed of light. They can be observed through the stretching and compression of the objects they traverse. Gravitational wave are produced by some of the most energetic and dramatic phenomena in the cosmos, including black holes, neutron stars and supernovae. Their discovery should help to address a number of fundamental questions in physics, from the evolution of stars and galaxies to the origin of dark energy and the nature of space-time itself. The Laser Interferometer Gravitational-wave Observatory (LIGO) is an international experiment for the detection of gravitational waves. LIGO's design uses a laser interferometer to measure with high precision the time it takes light to travel between suspended mirrors. The Advanced LIGO interferometers, currently being installed, will be the world's largest precision optical instruments and among the most sensitive scientific instruments ever built. In this talk we present an overview of the physics (and the challenges) of the LIGO experiment.
Dec 04 2012 16:00	Room 005	Luca Maccione (LMU, Munich and Max Planck Institute)	Propagating cosmic rays in the galaxy and in the heliosphere
ABSTRACT: Before being detected at Earth, cosmic rays at GeV energies undergo significant energy losses while diffusing in the solar system. These effects depend on the polarity of the solar magnetic field and therefore vary with the solar cycle. Accounting for them has become crucial in order to understand the propagation of cosmic rays in the Galaxy, thanks to the high precision data available nowadays. After having discussed the general features of galactic and solar propagations and the numerical techniques needed to describe them, we will show as a prime example that the puzzling discrepancy between the low-energy positron fraction measured by PAMELA and AMS-01 is easily explained by their different data-taking epochs. We will also show that the observed spectra of CR light nuclei can be reproduced within the same galactic and solar-system propagation model.
Nov 29 2012 16:00	Room 135	Yannis Bardoux (LPT, Orsay)	How to shape a black hole with matter fields
ABSTRACT: The main interest of the work exposed in this seminar is to explore new black hole solutions in a more general framework than General Relativity. A first extension will be detailed with the introduction of higher dimensions and p-form fields. These fields constitute the natural generalization of the electromagnetic interaction. We will build in this context new static black hole solutions where p-form fields allow to shape the geometry of the horizon. If time permits, we will explain the extension of this result in Einstein-Gauss-Bonnet gravity, which is the general extension of Einstein theory in 6 dimensions that produces second order field equations.\r\nSecondly, we will study a generalization of General Relativity in dimension 4 whose modification is induced by a conformally coupled scalar field. We will exhibit a new black hole solution with a NUT parameter using an elegant integration technique. After that, using our shaping trick in this framework, we will present a new black hole solution with a flat horizon in the presence of axionic fields. To conclude, we will examine phase transition phenomena in this context.
Nov 15 2012 16:00	Room 135	Sergey Sibiryakov (INR, Russian Academy of Science)	Testing Lorentz invariance of dark matter
ABSTRACT: I will discuss the possibility to constrain deviations from Lorentz invariance in dark matter (DM) with cosmological observations. Breaking of Lorentz invariance generically introduces new light gravitational degrees of freedom, that can be represented by a dynamical timelike vector field. If DM does not obey Lorentz invariance, it couples to this vector field, which affects the inertial mass of small DM halos leading to violation of the equivalence principle. However, for large enough lumps of DM a chameleon-type mechanism is identified that restores the inertial mass to its standard value. The above effects modify the dynamics of gravitational clustering. Two prominent features are a scale dependent enhancement in the growth of structure and a scale dependent bias between DM and baryon density perturbations. The comparison with the measured power spectra of the cosmic microwave background and matter distribution in principle allows to bound the departure from Lorentz invariance of DM at the per cent level.
Nov 13 2012 16:00	Room 005	Marcello Musso (UCL Louvain)	Non-Gaussian halo statistics from excursion sets
ABSTRACT: The abundance of gravitationally bound objects of a given mass (the halo mass function) is an important tool to predict the effect of non-Gaussian initial conditon on the process of structure formation, and to constrain the amount of primordial non-Gaussianity in cosmological perturbations. In the excursion set formalism the mass function is mapped into the first crossing probability of random walks through a threshold, where each walk is given by the average of the matter density over a set of volumes corresponding to a set of mass scales. The main technical difficulty of this approach has always been the presence of strong correlations between the steps of the walks. I will present a novel solution to deal with these correlations for a Gaussian field, and show how to incorporate non-Gaussianity. The extension of this method to other probes of non-Gaussianity in Large Scale Structure (like the scale dependent bias) will also be described.
Mar 20 2012 16:00	Room 005	Christoph Weniger (MPI for Physics, Munich)	Gamma-ray Lines & Co. in Indirect Searches for Dark Matter
ABSTRACT: Searches for signatures from dark matter annihilation or decay in the cosmic gamma-ray fluxes are plagued by the question of how to disentangle the astrophysical backgrounds from a potential dark matter signal. Fortunately, most dark matter models feature very sharp signatures in their gamma-ray energy spectrum, coming from monochromatic photons, final-state radiation or virtual internal bremsstrahlung. These features could appear above the continuous astrophysical backgrounds as clear smoking-gun signatures for dark matter. I will discuss in how far ongoing experiments like the Fermi LAT, or future Air Cherenkov Telescopes like the CTA, do or do not have the potential to discover these signatures in the next future. In fact, we already find weak evidence for a line-like signature at ~130 GeV in the galactic center observation of the Fermi LAT.
Feb 07 2012 16:00	room 005	Viatcheslav Mukhanov (LMU)	Quantum origin of the universe's structure
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Jun 14 2011 17:00	SISSA, room 005	John Kelley (University of Massachusetts, USA)	A New Window onto Ultra-high Energy Cosmic Rays: Super-hybrid Air Shower Observations at the Pierre Auger Observatory
ABSTRACT: Ultra-high-energy cosmic rays, with energies exceeding 10²⁰ eV, are the most energetic particles in the Universe, and yet we still know little of their origin or composition. The Pierre Auger Cosmic Ray Observatory, completed in 2008 and instrumenting an area of over 3000 km² in Argentina, has produced the most detailed measurements to date of these particles, including their arrival directions and energy spectrum, by employing hybrid observations of air showers with particle detectors and fluorescence telescopes. To fully determine the properties of the cosmic rays at the highest energies, however, requires new techniques, such as radio detection of air showers. With this goal in mind, we have constructed the Auger Engineering Radio Array (AERA), presently consisting of 21 radio-detection stations in Argentina. After reviewing Auger's recent results, I will explain the radio detection technique, its advantages and challenges, and show the first hybrid and super-hybrid cosmic ray events from AERA.
Apr 05 2011 16:00	SISSA, room 005	Albert Roura (Albert Einstein Institute, Potsdam, Germany)	Quantum effects and the stability of de Sitter spacetime
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Feb 22 2011 16:00	SISSA, room 005	Robert Wagner (Max Planck Instutute for Physics, Munich, Germany)	Recent Results from the MAGIC Telescopes
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Dec 02 2010 16:00	SISSA, room 135	Sudipta Sarkar (University of Maryland, USA)	Membrane Paradigm in f(R) gravity
ABSTRACT: The membrane paradigm is the remarkable view that, to an external observer, a black hole appears to behave exactly like a dynamical fluid membrane, obeying pre-relativistic equations. We extend the existing membrane formalism for General relativity to black holes in any general f(R)-theory of gravity and derive the stress tensor and various transport coefficients of the membrane fluid. The membrane turns out to behave like a non-Newtonian fluid except for the case of General Relativity. We also derive dynamical equations describing the fluid membrane. This result establishes the general analogy of the properties of black hole horizon with fluid mechanics beyond General Relativity to any general f(R) gravity theory.