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recent progress in numerical modeling of magnetically-dominated plasmas and show applications to pulsar magnetospheres in increasing levels of realism, including ideal and resistive force-free,

relativistic MHD and kinetic models. The knowledge of the magnetospheric shape together with the new observations of gamma-ray emission from pulsars with Fermi telescope allow to directly constrain the location and physics of the acceleration regions in the magnetosphere and the origin of high energy emission. The pulsar magnetosphere is a prototype for other strongly magnetized

astrophysical objects, and I will discuss how the lessons from pulsar modeling can be useful in predicting EM counterparts to gravitational wave sources.]]>

as almost-model-independent smoking guns for exotic particles and modified gravity, as well as their limitations in realistic astrophysical scenarios, are discussed.]]>

WDNS systems - the neglected child among compact binaries - generate detectable gravitational waves (GWs) and may also generate observable electromagnetic (EM) signals. One of the most fascinating aspects about these systems is that they are known to exist, but the final fate of massive, merged WDNSs remnants is currently work in progress. Determining the fate of WDNS remnants will be important for interpreting observations from future transient surveys. I will review recent work that provides insight into the physics of WDNSs remnants.

Black hole - neutron star systems are among the most promising sources for gravitational waves, and at the same time also possible sources of detectable precursor and aftermath EM signals. I will present recent the results from general relativistic force-free simulations of binary BHNSs and a type of EM precursor signatures expected from these systems.

]]>Einstein's field equations inside a cylindrical region, given suitable initial

and boundary data. We analyze the restrictions on the boundary data that result

from the requirement of constraint propagation and the minimization of spurious

reflections, and choosing harmonic coordinates we show how to cast the problem

into well-posed form. Then, we consider the particular case where the boundary

represents null infinity of an asymptotically flat spacetime. Here, the rôle of

the boundary conditions is to provide adequate regularity and gauge conditions

at infinity.

As an application of our setup we mention ongoing work on

the computation of quasi-stationary scalar field configurations on a

non-rotating supermassive black hole background.]]>

effects in the waveforms, existing and future gravitational-wave detectors

therefore provide a natural way to test gravity in strong-field, highly

dynamical regimes.

In the first part of my talk, I will show that the

inclusion of the spins in the gravitational templates for future space-based

detectors will permit testing scenarios for the formation and cosmological

evolution of supermassive black holes, and possibly shed light on models of

galaxy formation. In the second part, I will show that the effective-one-body

(EOB) model provides an efficient way to account for spin effects in both the

dynamics and waveforms, by combining information from post-Newtonian theory,

the self-force formalism, and numerical-relativity simulations.]]>

Thermodynamic instability of a family of black holes need not imply dynamic instability because the perturbations towards other members of the family will not, in general, have vanishing linearized ADM mass and/or angular momentum. However, we prove that all black branes corresponding to

thermodynmically unstable black holes are dynamically unstable, as conjectured by Gubser and Mitra. We also prove that positivity of $mathcal E$ is equivalent to the satisfaction of a ``local Penrose inequality,'' thus showing that satisfaction of this local Penrose inequality is necessary and sufficient for dynamical stability.]]>

the Einstein equations, as well as what this all means for the singular boundary

of generic space times within black hole regions.]]>

Based on arXiv:1405.4243 ]]>

Optomechanics experiments can also be used to search for possible deviations from standard quantum mechanics when macroscopic objects are involved. In this case, experiments are designed to highlight as much as possible the quantum-state evolution of the macroscopic objects. It is hoped that these macroscopic quantum mechanics experiments will either lead our way toward new physics, or at least put experimental constraints on how standard quantum mechanics might be modified.

]]>References

[1] JW Armstrong, Living Rev. Relativity 9, (2006), 1 [2] AC Vutha, arXiv:1501.01733 (2015)

]]>black holes exhibit novel chemical-type phase behaviour, hitherto unseen. ]]>

entanglement entropy at subleading orders in N (on the boundary) or

hbar (in the bulk). This involves a new concept of "quantum extremal

surfaces" defined as the surface which extremizes the sum of the area

and the bulk entanglement entropy. This conjecture reduces to

previous conjectures in suitable limits, and satisfies some nontrivial

consistency checks. Based on arXiv:1408.3203 ]]>

References:

[1]

[2]

[3]

]]>

For early universe cosmology before the formation of stars and galaxies, the mass $m_phi$, determined by the scalar field $mu(x)$, is bigger, $m_phi >> 2.6times 10^{-28},eV$, and can act as an ultralight cold dark matter photon with gravitational strength coupling to matter. The modified gravity can fit the cosmological data up to the epoch when stars and galaxies are first formed, and when the $phi_mu$ field density $rho_phi$ is significantly diluted compared to the baryon density $rho_b$. After the commencement of the star and galaxy formation epoch, the modified gravity without dark matter takes over. A prediction of the matter power spectrum is made of the first formation of galaxies that do not have dark matter halos. The lack of detectability of the gravitationally sourced dark photon can explain why no convincing detection has so far been made of dark matter particles in laboratory and satellite experiments.

The modified gravity theory vacuum field equations with a smooth vector field source energy-momentum tensor are solved to produce a black hole that differs from the Schwarzschild, Kerr and Reissner-Norstr"om black holes when the parameter $alphaneq 0$. A modified gravity solution is also obtained from a nonlinear regular vector field solution that is regular at $r=0$. This solution can describe a black hole with two horizons as well as a no black hole solution with no horizon. The black hole MOG solutions possess a photosphere and they cast a shadow against a bright background. The sizes and deformations of these shadows can be detected by the VLBI and Event Horizon (EHT) project. These observations will be able to test general relativity for strong gravitational fields. A traversable wormhole can be constructed using the modified gravity theory with a wormhole throat stabilized by the gravitationally sourced repulsive vector field.

]]>The masses and interactions of the different flavors show a very hierarchical structure and the origin of these hierarchies remains an unsolved mystery of particle physics. The same hierarchies lead to a very high sensitivity of flavor changing processes to new undiscovered particles even outside the reach of direct searches at particle colliders.

In this colloquium I will present recent developments in constructing a theory of flavor and highlight the complementarity of flavor, Higgs, and collider physics in searching for new phenomena at the TeV scale and beyond. ]]>

duals of theories deformed by localized Dirac delta sources for scalar

operators. We perform two different constructions, one at zero and

the other at nonzero temperature. Surprisingly we find that imposing the preservation of scale

invariance at zero temperature requires the bulk scalar self-interaction potential to be

the one found in a certain Kaluza-Klein compactification of 11D supergravity.

The gravitational setup seems a-priori to be quite unusual and challenging

from the numerical relativity perspective. ]]>

I will show how to embed this problem in holography, where such effective actions can be computed explicitly for the class of relativistic conformal fluids. In particular I will identify the geometric counterpart of certain Goldstone bosons, the light degrees of freedom responsible for the low energy excitations in hydrodynamics. Moreover I will show how the underlying UV Schwinger-Keldysh structure arises at the level of the effective action.

]]>constraints are available from observations? Based on a precise

mapping between particle production in cosmology to resistivity in disordered, quasi one-dimensional wires, I will provide a statistical framework to resolve such seemingly intractable calculations. A number of phenomenon in disordered wires find an analogue in particle production. For example, Anderson localization in quasi one-dimensional wires can be directly mapped to exponential particle production in the early universe. The talk will be focussed on the general framework and some toy examples, though in the end I will discuss possible (future) applications to calculating observables.

]]>mode functions, which are the fundamental building blocks in perturbative treatments of nonlinearities. While complicated explicit expressions for these mode functions are available in the literature, they hide a good deal of the elegant underlying structure dictated by the AdS symmetries. Extending the mode functions in the flat embedding space (in which the AdS space can be realized as a hyperboloid) results in families of homogeneous polynomials, on which the AdS isometries act in a straightforward manner. This suggests a simple proof of important selection rules in nonlinear perturbation theory.

Studies of multiplet structures of the mode functions furthermore reveal a relation to the Higgs oscillator, a well-known quantum-mechanical superintegrable system. This AdS connection leads to an explicit construction of the hidden symmetry generators for the Higgs oscillator, a long-standing problem in mathematical quantum mechanics.

]]>theoretical physics due to the AdS/CFT correspondence. However, the

question of stability of AdS space is unanswered till now. After

giving the motivation for studies of asymptotically AdS spaces, I will

review dynamics of such spacetimes in the context of AdS instability

problem. This survey will include: evidence for instability of AdS

space, existence and properties of time-periodic solutions, and

finally an application of analytical technique called multiscale or

resonant approximation approach. If time permits, I will comment on

other asymptotically AdS solutions. Along with the results, I will

highlight some details of methods relevant to the topic. ]]>

gravitational wave measurements, makes black holes into

nature's laboratories to search for new light bosons. We will present

analytic results for superradiance of light vector (spin-1) particles,

valid in the regime where the vector's Compton wavelength is much

larger than the horizon size of a black hole. If superradiance is

efficient, the occupation number of the vectors in the black hole's

vicinity grows exponentially and the black hole spins down. We will

present preliminary signatures of this process, including black hole

spin measurements and gravitational wave signals. Current measurements

of black hole spins disfavor a range of masses of (gravitationally

coupled) vectors. Vectors annihilating to gravitons would emit

strong monochromatic gravitational wave signals, which may be

visible in future LIGO observations. ]]>

Related Arxiv #: https://arxiv.org/abs/1706.06155 ]]>

One of the preferred candidates are globular clusters, massive systems of very old stars densely packed together and bound together by gravity. Globular clusters are factories for black hole binary mergers. But we are only able to observe these factories in operation now. In order to understand how they were built and the treasures they should be expected to produce at present, we must somehow rewind their evolution over billions of years to say something about the initial conditions. Only then will we be able to understand how these beasts birth BH binaries, and are contributing to the gravitational waves currently being observed by aLIGO. After a brief overview of the concept of chaos, I will discuss recent progress in advancing our understanding of the origins of BH-BH mergers.

]]>In this seminar, we address its extension to modified gravities, considering first the example of massless scalar-tensor theories (ST). We reduce the ST two-body dynamics, which is known at second post-Keplerian order, to a simple parametrized deformation of the general relativistic EOB Hamiltonian, and estimate the ST corrections to the strong-field regime; in particular, the ISCO location and orbital frequency.

We then discuss the class of Einstein-Maxwell-dilaton (EMD) theories, which provide simple examples of "hairy" black holes. We compute the EMD post-Keplerian two-body Lagrangian, and show that it can, as well, be incorporated within the EOB framework. Finally, we highlight that, depending on their scalar environment, EMD black holes can transition to a regime where they strongly couple to the scalar and vector fields, inducing large deviations from the general relativistic two-body dynamics.

]]>symmetries. These are genuine phase space symmetries that stand in contrast to the more familiar symmetries of the configuration space

discussed in truncated versions of Noether's theorem. Proceeding to a relativistic description, I will demonstrate that such symmetries -- encoded

in the so called Killing-Yano tensors -- play a crucial role in the study of rotating black holes described by the Kerr geometry. Even more remarkably, I will show that one such special symmetry is enough to guarantee complete integrability of particle and light motion in general rotating black hole spacetimes in an arbitrary

number of spacetime dimensions. Recent developments on the separability of test fields in these spacetimes will also be discussed. ]]>

our results showing that no continuous

degenerations exist between the shadows of observers at any point in the exterior region of any Kerr-Newman black hole spacetime of unit mass. Therefore an observer can, by measuring the black holes shadow, in principle determine the angular momentum and the charge of the black hole under observation, as well as his radial distance from the black hole and his angle of elevation above the equatorial plane. ]]>

lead to detailed investigations of the origin of these objects. In my talk

I will discuss the questions: What is the astrophysical origin of these objects?

What do these detections tell us about the formation of black holes and neutron stars?

What are the main problems that they pose?

What to expect in the coming gravitational observations? ]]>

The formation of a gravitational vacuum condensate star with a p=−ρ interior solves these problems and remarkably, actually follows from Schwarzschild's second paper over a century ago. The surface tension of the condensate star surface is the difference of equal and opposite surface gravities between the exterior and interior Schwarzschild solutions. The First Law is then recognized as a purely mechanical classical relation at zero temperature and zero entropy. The Schwarzschild time of such a non-singular gravitational condensate star is a global time, fully consistent with unitary time evolution in quantum theory.

The advent of BH imaging by the EHT and Gravitational Wave Astronomy with LIGO should allow for observational tests of the gravastar hypothesis, particularly in the discrete surface modes of oscillation and GW resonances or “echoes,” which may be observable by advanced LIGO and successor GW detectors.

]]>ingredient of consistent thermodynamics is to ensure that the system is not over-constrained by including the possibility of varying the string tensions that are responsible for the acceleration of the black hole. The first law assumes the standard form, with the entropy given by one quarter of the horizon area and other quantities identified by standard methods. The dual

energy-momentum tensor can be written as a three-dimensional perfect fluid plus a non-hydrodynamic contribution. Some novel thermodynamic phase behavior related to the black hole acceleration will also be discussed. ]]>

have opened a new and exciting window into observing the Universe.

Persistent sources of gravitational waves must also exist; searches for

continuous gravitational-wave signals generally look for signals from

non-axisymmetric neutron stars, but are also suitable for continuous

gravitational waves from axion annihilations in clouds around black

holes. I will discuss the expected axion annihilations signal from an

astrophysical standpoint, starting from the Galactic isolated black hole

population. ]]>

the beginning of a new era of astrophysical observations. When the

emitters include a compact object like a neutron star, the GW signal

is accompanied by emissions in different bands, e.g. X-rays,

gamma-rays, optical and neutrinos. The interpretation of such

multimessenger signals allows us to gain a deeper understanding of the

interiors of compact objects. One main challenge is to link our

knowledge of nuclear interactions to macroscopic properties of dense

objects in the Universe. In this talk I will discuss selected aspects

along the interface of nuclear physics and astrophysics ]]>

I will show how the information carried in the gravitational wave signal of GW170817 can be used to constrain the EOS at densities above saturation and what we can learn about the possible existence of phase transitions. I will

also comment on how we can improve on those limits with upcoming observations of the NICER mission.In the second part of the talk I will focus on what we can learn about exotic states of matter from neutron star mergers.I will comment briefly on the impact of high spins in mergers and the importance of accurate numerical modelling in the context of these studies.Finally I will show how neutron star mergers can be used to study quark phase transitions and the phase diagram of QCD. ]]>

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]]>Previous studies considered the Doppler effect on the phase of GWs as a potential signature of a time-dependent velocity of the source. However, the Doppler shift only accounts for the time component of the wave vector, and in principle motion also affects the spatial components. In my talk I discuss the latter effect, known as “aberration” for light, for GWs and how it affects the waveform modeling of an accelerating source. I show that the additional aberrational phase shift could be detectable in two astrophysical scenarios, namely, a recoiling binary black hole (BBH) due to GW radiation and a BBH in a triple system.

Further, I discuss how adding the aberrational phase shift in the waveform templates could significantly enhance the detectability of moving sources.

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]]>Apart from being ionizing sources, stripped stars are also interesting to consider as gravitational wave emitters. Creating a population model, we predict that several stripped stars orbiting compact objects will be detectable by LISA.

]]>I will present a new method to obtain constraints on the lifetime of high-redshift quasars, based on measurements of the sizes of ionized regions around quasars, known as proximity zones. The sizes of these proximity zones are sensitive to the lifetime of the quasars, because the intergalactic gas has a finite response time to the quasars’ radiation. Applying this method to quasar spectra at z>6, we discover an unexpected population of very young quasars, indicating lifetimes of only ~10,000 years, several orders of magnitude shorter than expected. I will discuss the consequences of such short lifetimes on the quasars' ionizing power, their black hole mass accretion rates, and highlight tensions with current theoretical models for black hole formation. Furthermore, I will present several modifications to the current SMBH formation paradigm that might explain our findings and show how we aim to disentangle the various scenarios by means of future observations with the upcoming James Webb Space Telescope, in order to shed new light onto the formation and growth of the first SMBHs in the universe.

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