Date 
Room 
Speaker 
Title 
May 28 2019
14:00 
004

Pawan Kumar
(University of Texas at Austin)

The Mystery of Fast Radio Bursts 
ABSTRACT: Fast radio bursts (FRBs) are millisecond duration transient events of unknown physical origin. At least one FRB is located at a distance of several billion light years, and CHIME has established that there are many FRBs that repeat. Using very general arguments I will show that the radio emission is coherent, the magnetic field strength associated with the source of these events is 10^{14} Gauss or more, and the electric field is of order 10^{10} esu. I will describe recent works that magnetic field distortion and reconfiguration is responsible for the strong electric field and the coherent radiation produced in these enigmatic events. I will also address the polarization properties of the wellknown repeater. 
May 16 2018
14:00 
Room 005

Jishnu Bhattacharyya
(Perimeter Institute)

Lorentz violation, Penrose type energy mining and perpetual machines 
ABSTRACT: Black hole solutions in locally Lorentz violating theories of gravity generically admit various \"effective horizons\", acting as causal boundaries for particles of different speeds. The existence of multiple horizons has been used in the past to claim that black holes in such theories are unstbale (e.g., under Penrose type energy minining) and capable of violating the cherished generalized second law of thermodynamics. In this talk, I would like to revisit such claims carefully and argue that such processes can take place only if the background satisfies certain geometric properties. In particular, black hole solutions of *consistent* locally Lorentz violating theories of gravity (e.g., Einsteinaether theory and Horava gravity) do not seemingly allow for such energy mining. 
Jun 13 2017
14:00 

Silvio Bonometto
(INAFOATS, Trieste, IT)

Cosmologies with strong DMDE coupling and a WDM component 
ABSTRACT: In the era of big projects to inspect the DE nature, new cosmological models are welcome when predicting effects such experiments can test. Accordingly, cosmologies with strong DMDE coupling and WDM,predicting a null result in planned Big Physics programs, apparently diverge from the mean stream of thought. Being based on the finding of a kinetic attractor solution in the radiative era, they however meet quite a few existing datasets, otherwise hard to reconcile with LCDM models, even with extreme stretching of baryonic physics. Among them, let me list MW and M31 satellites, dwarf galaxy profiles, concentration distribution, Lymanalpha excess; not to forget the severe conundrums infecting LCDM models and the natural option, within SCDEW, that the same scalar field is Dark Energy and plays a key role in inflation. 
May 16 2017
14:00 

Jishnu Bhattacharyya
()

Lorentz violation, Penrose type energy mining and perpetual machines 
ABSTRACT: Black hole solutions in locally Lorentz violating theories of
gravity generically admit various "effective horizons", acting as causal
boundaries for particles of different speeds. The existence of multiple
horizons has been used in the past to claim that black holes in such
theories are unstable (e.g., under Penrose type energy mining) and capable
of violating the cherished generalized second law of thermodynamics. In this
talk, I would like to revisit such claims carefully and argue that such
processes can take place only if the background satisfies certain geometric
properties. In particular, black hole solutions of *consistent* locally
Lorentz violating theories of gravity (e.g., Einsteinaether theory and
Horava gravity) do not seemingly allow for such energy mining. 
May 11 2017
14:00 
Room 005

Christian Pfeifer
(Tartu University)

Curved Spacetimes with local kappaPoincare dispersion relation 
ABSTRACT: The kappaPoincare dispersion relation is one of the most studied
dispersion relation in the context of quantum gravity phenomenology. It
emerges as Casimir operator of the kappaquantum deformation of the
Poincare algebra and can be connected to quantum gravity by identifying
the deformation parameter kappa with the inverse of the Planck length.
Phenomenological studies about the observable consequences on particle
motion induced by the kappaPoincare dispersion relation focused so far
on maximally symmetric spacetimes. In this talk we will construct
kappadeformations of generically curved spacetimes, which have the
property that locally they look like Minkowski spacetime equipped with
the kappaPoincare dispersion relation.
This can be understood as generalization from local Lorentz invariant
spacetimes of general relativity to local kappaPoincare invariant
spacetimes. Having established the notion of local kappaPoincare
spacetimes e study the kappadeformations of Schwearzschild and FLRW
geometry including observable effects of the deformation on the photon
sphere, the redshift and the time of arrival of photons. 
Apr 12 2017
14:00 

Riccardo Catena
(Chalmers University of Technology, Sweden)

Non relativistic effective theory methods for dark matter detection 
ABSTRACT: Unveiling the nature of dark matter is arguably one of the most
pressing research questions in science today. The direct detection technique will be pivotal in this context. It primarily searches for nuclear recoil events induced by the scattering of Milky Way dark matter particles in lowbackground detectors. A Non Relativistic Effective Field Theory (NREFT) has been developed in the past few of years to interpret results from direct detection experiments in a modelindependent manner, and to combine them with dark matter searches at neutrino telescopes. In this talk, I will apply the NREFT formalism to three problems: 1) the compatibility of DAMA with null results; 2) the capture of dark matter in the Sun and Earth; 3) the distortion of the dark matter speed distribution due to Earthscattering events. 
Mar 14 2017
14:00 
128129

Dr. Mehdi Saravani
(Nottingham University)

Nonlocality and dark matter? 
ABSTRACT: I will review recent works in nonlocal quantum field theory models
motivated by the Causal Set approach to quantum gravity. These models
generically include a "continuum" massive set of field excitations,
contrary to "isolated" mass excitations in local quantum field
theories. I will provide an example of phenomenological signatures of
these excitations.
Finally, I will explore the idea of the "continuum" modes playing the
role of dark matter, argue why they are a natural dark matter
candidate and discuss open problems in this approach. 
Feb 21 2017
2:00 
Room 136  SISSA Main Building,

Sumati Surya
(Raman Research Inst., Bangalore)

A study of two dimensional causal set quantum gravity 
ABSTRACT: I will begin with an introduction to causal set quantum\r\ngravity. In this approach\r\nthe spacetime continuum is replaced by an underlying locally finite\r\npartially ordered set, with the order relation corresponding to the\r\ncausal order on spacetime events. I will focus on a particular route\r\nto quantisation that takes its cue from the path integral\r\nconstruction. As in other approaches it is useful to analytically\r\ncontinue from a quantum to a statistical partition function, but here\r\nit is done without changing the Lorentzian character of the causal\r\nset. I will present results from Markov Chain Monte Carlo simulations\r\nof a two dimensional restriction of the theory. This theory exhibits\r\na first order phase transition from an ordered to a disordered phase. \r\nThe disordered phase is approximated by flat 2d Minkowski spacetime \r\nwhile the ordered phase possesses a high degree of causal\r\nconnectivity, with echoes of inflation. The system moreover obeys a\r\nconsistent finite size scaling behaviour, which suggests that one is\r\nin the \"large N\" regime. 
Jul 06 2016
14:00 
Room 005

Chunshan Lin
(Yukawa Institute for Theoretical Physics, Kyoto University)

Do we have to modify gravity in the very early universe? 
ABSTRACT: Do we have to modify gravity in the very early universe? It depends. In my talk I will introduce some wouldbe strong evidences if they are detected and/or confirmed by near future experiments. 
Jun 16 2016
14:00 
Room 004

Michele Vallisneri
(Jet Propulsion Laboratory, California Institute of Technology)

LIGO vs pulsar timing: stellarmass black holes now, massive black holes soon 
ABSTRACT: On September 14, 2015, the two LIGO detectors simultaneously observed a transient gravitationalwave signal, which was named GW150914. The signal fits very precisely the general relativistic prediction for the inspiral, merger, and ringdown of a pair of black holes, with component masses greater than was thought possible for stellarmass systems. This was the first direct detection of gravitational waves and the first observation of a binary black hole merger. I describe the detection and its implications for astrophysics and fundamental physics.rnOn the other side of the spectrum, at very low frequencies, pulsartiming arrays have reached a mature stage where observations are beginning to constrain astrophysical expectations for the mergers of massive blackhole binaries at the centers of galaxies. A positive detection of the stochastic background from these systems is expected within the next ten years. I discuss this program, its prospects, and its peculiar requirements in terms of observations and analysis. 
Jun 14 2016
14:00 
Room 004

Andrea Dapor
(University of Erlangen)

How classical spacetimes could emerge from quantum gravity 
ABSTRACT: One of the central questions of Quantum Gravity is: how to recover classical spacetime from a fundamentally quantum description of geometry? Consider an experimentalist: she does not measure geometry directly, but rather infers it by studying the propagation of matter. Hence, if there are two geometries producing the same matter dynamics, then they should be considered physically equivalent. We will take this idea seriously, and apply it to QFT on quantum spacetime, finding that the dynamics of matter is equivalent to that of QFT on an effective classical spacetime. In this sense, we can think of such effective spacetime as emerging from the interaction between matter and quantum geometry. We will apply this general machinery to the homogeneous case (with attention to FLRW and Bianchi I quantum cosmologies), finding that under certain conditions the emergent spacetime breaks local Lorentz symmetry and the Universality principle. If there is enough time, we will embed these findings within physical cosmology (in the context of m^2inflation), and discuss a possible measurable signature in the modified dispersion relations of scalar and tensor modes. 
May 05 2016
14:00 
Room 5

Dr. Eduardo Martin Martinez
(Institue of Quantum Computing, University of Waterloo and Perimeter Institute, Canada)

Timelike information broadcasting, entanglement harvesting and Cosmology 
ABSTRACT: The strong Huygens principle states that the radiation Green's function has support only on the light cone. In the context of relativistic quantum communication, the violation of this principle implies that there can be a leakage of information towards the inside of the light cone, even for massless quantum fields. When this happens much more information reaches us through timelike channels (not mediated by real photons) than it is carried by rays of light, which are usually regarded as the only carriers of information. In this talk, we will discuss how this may have unexpected consequences in cosmological scenarios both in a standard cosmological model (in general relativity) and in the presence of a big bounce which removes the relativistic big bang singularity. 
Mar 15 2016
14:00 
room 137

Francesco Cianfrani
(University of Wroclaw, Poland)

Quantum Reduced Loop Gravity 
ABSTRACT: I will give a general overview on Quantum Reduced Loop Gravity, focusing on the relationship with Loop \r\nQuantum Gravity and its potential applications. 
Dec 15 2015
14:00 
Room 005

Prof. Thomas Sotiriou
(University of Nottingham)

Lorentz violations, causality, and black holes 
ABSTRACT: I will discuss some basic aspects of causality in theories that violate Lorentz symmetry. I will then focus on theories that have a preferred foliation that determines the causal structure and I will define the appropriate notion of black hole in such theories. Finally, I will explore some basic aspects of this new kind of black holes. 
Dec 10 2015
14:00 
Room 137

Prof. Fabrizio Tavecchio
(INAF, Osservatorio Astronomico di Brera)

Blazars: astrophysical laboratories and astroparticle beams 
ABSTRACT: Blazars are the sources dominating the extragalactic sky at gammaray energies. Their nonthermal emission, dominated by the relativistically boosted emission of a relativistic jet powered by a supermassive black hole, is the ideal tool to study the physical processes acting in jets and in the black hole vicinity. Their powerful highenergy beam can also be used to probe the extragalactic background light and the intergalactic magnetic field. In recent years blazars have been also considered as the possible sources of highenergy neutrinos and rnultrahigh energy cosmic rays. After a brief general introduction I will discuss the present status of the research in the field, highlighting some recent developments. 
Nov 05 2015
15:00 
Room 004

Prof. Shinji Mukohyama
(Yukawa Institute for Theoretical Physics, Kyoto University)

Massive gravity and cosmology 
ABSTRACT: The search for a consistent theory of finiterange gravity is a longstanding problem and well motivated by both theoretical and observational considerations. On the theoretical side, whether there exists such a consistent extension of general relativity by a mass term is a basic question of classical field theory. After Fierz and Pauli's pioneering attempt in 1939, this issue has been attracting a great deal of interest. On the observational side, continuingrnexperimental probes of gravity have revealed new unexpected phenomena at large scales. One of the most profound discovery is the cosmic acceleration, which was found in 1998. The extremely tiny energyscale associated with the cosmic acceleration hints that gravity might needrnto be modified in the infrared. The massive gravity is one of the most interesting attempts in this direction. In this talk, after reviewing the history and recent developments of massive gravity, I will describe cosmological solutions and their stability. 
Oct 14 2015
11:00 
TBA

Prof. Robert Brandenberger
(McGill University, Montreal, Quebec)

Searching for Cosmic Strings in New Observational Windows 
ABSTRACT: Cosmic strings solutions exist in many particle physics models beyond the Standard Model. IfrnNature is described by such a model, then causality tells us that a network of strings will form in the early universe and will persistrnto the present time. The gravitational effects of these strings leave behind specific imprints in observational windows such asrnCMB temperature maps, CMB polarization maps, and 21cm redshift maps. I will discuss these signals and discuss what one can learn about particle physics by searching for them. 
Oct 13 2015
14:00 
Room 004

Dr. Francesca Vidotto
(Radboud University Nijmegen, Netherlands)

Possible quantumgravity signals from primordial black holes 
ABSTRACT: Quantum gravity may allow black holes to tunnel into white holes. If so, the lifetime of a black hole would be shorter than the one given by Hawking evaporation, solving the information paradox. More interestingly, this could open to a new window for quantumgravity phenomenology, in connection with the existence of primordial black holes. I discuss in particular the power of the associated explosion and the possibility to observe an astrophysical signal in the radio and in the gamma wavelengths. 
Feb 10 2015
16:00 
Room 005

Chiara Arina
(Institut d'Astrophysique de Paris)

Dark Matter direct detection and Bayesian statistics 
ABSTRACT: Abstract: Dark Matter direct detection experiments present an
ambiguous situation, with hints of WIMP detection at odds with
exclusion limits. Bayesian statistical methods offer a simple and
consistent framework for incorporating uncertainties into a
multiparameter inference problem. In this talk we apply these methods to a selection of experiments and discuss how astrophysical and particle
physics uncertainties affect the theoretical interpretation of
these bounds/hints. We then discuss the impact of going beyond the
spinindependent scalar interaction in term of compatibility among
experimental results. We conclude with the prospects for dark matter
direct detection experiments in the
forthcoming years. 
Dec 16 2014
16:00 
Room 005

Diego Blas
(CERN)

“Massive neutrinos and cosmological structure formation: analytical approaches beyond linear theory” 
ABSTRACT: Different observations have confirmed that neutrinos are massive particles, but the values of their masses are still unknown. Remarkably, cosmological observables, e.g. the power spectrum of the large scale structure, are\r\nvery sensitive to these fundamental quantities. In fact, it seems plausible that the first detection of the mass of the neutrinos will come from the next generation of cosmological experiments. In this talk, I’ll explain recent approaches to treat massive\r\nneutrinos in the linear and mildly nonlinear regime of cosmology. I will also show some of the observational consequences that appear in the matter power spectrum at large scales. 
Oct 07 2014
11:30 
room 005

Paolo Pani
(Instituto Superior Tecnico  Lisboa)

Black holes as stronggravity labs 
ABSTRACT: Black holes are multifaceted objects that probe the strongfieldrnnature of gravity and can be used to test fundamental physics. From anrnastrophysical standpoint, massive black holes may undergornsuperradiance instabilities in the presence of light bosonic fields.rnThis effect, together with precision measurements of the mass and spinrnof astrophysical black holes, has been used to constrain axions andrnultralight scalars, to derive bounds on light vector fields and on thernmass of the graviton, as well as to put intrinsic bounds on magneticrnfields near black holes and on the fraction of primordial black holesrnin dark matter. From a more fundamental perspective, various problemsrnrelated to blackhole formation in the gravitational collapse  suchrnas the appearance of singularities and the cosmic censorship  arernstill open. I present the theoretical potential of these phenomena asrnalmostmodelindependent smoking guns for beyondStandard Modelrnphysics, and recent developments on understanding the formation ofrnblack holes in general relativity. 
Apr 01 2014
14:00 
room 005

Fay Dowker
(Imperial College, London)

In search of lost time....in quantum gravity 
ABSTRACT: In some of the earliest existing records of human intellectual
exploration of the nature of the world, the dichotomy between a static view of the world (Being) and a dynamic view (Becoming) shows itself. The debate continues to this day and there is no consensus, though some
philosophers and physicists claim that General Relativity (GR) wins it for Being. I will describe why such a conclusion is drawn within GR. I will then show that developments in quantum gravity research seem to open the door once again to Becoming. I will raise the question as to whether, despite this progress, Mathematics could ever truly capture the
fleeting, dynamic quality of the world as we experience it. 
Mar 11 2014
14:00 
room 005B

Emanuele Berti
(University of Mississipi)

Fundamental physics and astrophysics of compactbinary mergers 
ABSTRACT: Compactbinary mergers are an ideal laboratory for strongfield gravitational physics. I will describe two lines of work illustrating this point.
In the first part of my talk I will discuss compact binaries as the main observational targets of upcoming gravitationalwave detectors, such as Advanced LIGO/Virgo, KAGRA, the Einstein Telescope and eLISA. It is imperative to develop a longterm strategy to learn as much as possible from individual gravitationalwave observations and
from the statistical properties of observed systems.
I will address two central questions in the development of this strategy:
1) Can we constrain the formation history of compact binaries using Earthbased and spacebased gravitationalwave observations?
2) What sort of strongfield tests of general relativity (if any) will be possible with Earth and spacebased detectors?
In the second part of the talk I will discuss compact binaries as "gedanken experiment laboratories" for strongfield gravitational physics. I will report results from numerical simulations of ultrarelativistic black hole collisions that highlight interesting properties of the strongfield dynamics of general relativity, including critical phenomena, the ultrarelativistic version of the
effacement principle, and the role of absorption in highenergy black hole encounters. 
Nov 27 2013
16:00 
SISSA  room 005

Alejandro Ibarra
(TU Munich)

Searching for spectral features in the gammaray sky 
ABSTRACT: The search for the gammarays which are presumably produced in dark matter annihilations is hindered by the existence of large, and still poorly understood, astrophysical backgrounds. In this talk we will emphasize the importance of sharp spectral features for the identification of a dark matter signal. We will review the status of the search of the various spectral features that arise in Particle Physics scenarios and we will discuss the interplay with other search strategies. 
Nov 26 2013
14:00 
SISSA  room 004

Ted Jacobson
(University of Maryland College Park)

Spacetime approach to forcefree magnetospheres 
ABSTRACT: This talk will review how forcefree magnetospheres of neutron stars and black holes convert rotational to electromagnetic energy, and will show how the theory becomes remarkably simple and elegant when treated relativistically with the help of differential forms. 
Nov 21 2013
14:00 
SISSA, Room 135

J.F. Kamenik
(Dept. of Physics, University of Ljubljana, Slovenia)

Dark side of Higgs boson 
ABSTRACT: I will discuss the impact of hypothetical new neutral light particles on the tiny width of a light Higgs boson. To this end, I will review the possible signatures in the Higgs decay modes with missing energy, including all the relevant effective interactions, whether renormalizable or not. This includes the fully invisible Higgs boson decay, as well as modes with SM gauge bosons or fermions in the final state. In many cases, simply preventing these modes from being dominant suffices to set tight modelindependent constraints on the masses and couplings of the new light states. Then I will apply this analysis to Higgs portal models of dark matter (DM), where DM is light enough to contribute to invisible Higgs decays. I will show that DM can be a thermal relic only if there are additional light particles present with masses below a few 100 GeV. Three concrete examples of viable Higgs portal models of light DM will be presented where the invisible Higgs decay constraint is not too restrictive, because it is governed by different parameters than the relic abundance. Implications of additional light particles for flavor violation and collider searches will be briefly discussed. 
Oct 24 2013
16:15 
SISSA  Big Meeting Room (7th floor)

Bill Unruh
(University of British Columbia, Canada)

Black hole entropy, unitarity, firewalls, etc 
ABSTRACT: In the past few months the black hole information problem has becomernproblematic. The argument has been made that if the black hole was created byrncollapse of a pure state, it will create a pure state after the evaporationrnhas finished, then there must be a "firewall", a very large flux of energyrnjust on or inside the horizon must exist. This talks will quiclky review thernargument, and give my take on the possibilities this creates for the bahaviourrnof black holes. 
Oct 22 2013
14:00 
SISSA, Room 005

L. Lehner
(Perimeter Institute for Theoretical Physics, Ontario, Canada)

Gravitational and (possible) electromagnetic signals from compact binaries 
ABSTRACT: Direct detection of gravitational waves is likely (hopefully!) happening in less
than a decade. Beyond what they can intrinsically tell us about gravity and
the systems that produce them, an exciting prospect is to detect signals
of multiple nature. This talk will examine a few relevant cases, what
might induce electromagnetic counterparts and how. 
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 nogo 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 spacetime in loop quantum gravity and signature change 
ABSTRACT: 
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 SuperKamiokande. 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
nongeometric 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 uptodate 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 yearold 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 Gravitationalwave Observatory 
ABSTRACT: Gravitational waves are distortions of the spacetime 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 spacetime itself.
The Laser Interferometer Gravitationalwave 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 lowenergy positron fraction measured by PAMELA and AMS01 is easily explained by their different datataking epochs. We will also show that the observed spectra of CR light nuclei can be reproduced within the same galactic and solarsystem 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 pform fields. These fields constitute the natural generalization of the electromagnetic interaction. We will build in this context new static black hole solutions where pform fields allow to shape the geometry of the horizon. If time permits, we will explain the extension of this result in EinsteinGaussBonnet 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 chameleontype 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)

NonGaussian 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 nonGaussian initial conditon on the process of structure formation, and to constrain the amount of primordial nonGaussianity 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 nonGaussianity.
The extension of this method to other probes of nonGaussianity 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)

Gammaray Lines & Co. in Indirect Searches for Dark Matter

ABSTRACT:
Searches for signatures from dark matter annihilation or decay in the cosmic
gammaray 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 gammaray
energy spectrum, coming from monochromatic photons, finalstate radiation or
virtual internal bremsstrahlung. These features could appear above the
continuous astrophysical backgrounds as clear smokinggun 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 linelike 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 
ABSTRACT: 
Jun 14 2011
17:00 
SISSA, room 005

John Kelley
(University of Massachusetts, USA)

A New Window onto Ultrahigh Energy Cosmic Rays: Superhybrid Air Shower Observations at the Pierre Auger Observatory

ABSTRACT: Ultrahighenergy cosmic rays, with energies exceeding 10^{20} 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 km^{2} 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 radiodetection 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 superhybrid 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 
ABSTRACT: 
Feb 22 2011
16:00 
SISSA, room 005

Robert Wagner
(Max Planck Instutute for Physics, Munich, Germany)

Recent Results from the MAGIC Telescopes 
ABSTRACT: 
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 prerelativistic 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 nonNewtonian 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. 