# DEPARTMENT OF PHYSICS / HIP JOINT COLLOQUIA / SEMINARS 2008

• Tuesday 15 January 2008 at 10.15 in E204: Kimmo Tuominen (Jyväskylä University and HIP)
Technicolor – a competitive mechanism for electroweak symmetry breaking
Abstract: The experiments at LHC are expected to determine the origin of weak gauge boson masses and point towards the theory of electroweak symmetry breaking. One possibility is technicolor where the Higgs boson is not a fundamental scalar particle but a composite, similar to the mesons in QCD. In this talk, I will begin with a brief introduction to technicolor. Then I will outline how to construct technicolor models which are not ruled out by current precision data and hence must be tested at LHC. Finally, I will spell out in detail the minimal model and discuss its low energy phenomenology and implications for colliders and cosmology.
• Tuesday 22 January 2008 at 10.15 in E204: Sean Nowling (HU and HIP)
Entanglement Entropy in Chern-Simons Field Theories
Abstract: In the FQH effect, one encounters topological phases of matter. Such phases are not characterized by any local order parameter and one needs new quantities to characterize the system’s phase. One such quantity is quantum entanglement entropy. In this talk, I shall review the behaviour of entanglement entropy in 1+1 dimensional conformal field theories. I shall then discuss entanglement entropy in 2+1 dimensional Chern-Simons theories, which are known to provide effective descriptions of FQH systems.
• Tuesday 29 January 2008 at 10.15 in E204: Vappu Reijonen (HIP, Magnus Ehrnrooth foundation fellow)
Static, spherically symmetric spacetimes in f(R) gravity models
Abstract: f(R) models are a class of modified gravity theories that can provide a gravitational alternative to dark energy. In this talk I will review static, spherically symmetric spacetime solutions of stars in f(R) models in metric and Palatini formalism. The modified field equations are derived, including the generalized Tolman-Oppenheimer-Volkoff equations for hydrostatic equilibrium, and they are studied both analytically and numerically with a specific interest in the Post-Newtonian limit and Solar System constraints.
• Tuesday 12 February 2008 at 10.15 in E204: Touko Tahkokallio (HIP)
Applications of AdS/CFT duality to heavy ion collisions
Abstract: I will briefly introduce AdS/CFT duality and present some of its applications to QCD and heavy ion collisions.
• Tuesday 26 February 2008 at 10.15 in E204: Teresa Marrodan Undagoitia (Technische Universität München)
Lena: a multipurpose detector for low energy neutrino astronomy
Abstract: LENA (Low Energy Neutrino Astronomy) is a proposed 50 kt liquid-scintillator multipurpose detector. The preferred location for the detector is the Pyhäsalmi underground mine in Finland. Due to a low energy threshold, high energy resolution, and a large detector volume, LENA could offer the possibility to answer various physics questions. The goals of LENA extend to the fields of astrophysics (e.g. the observation of supernova, diffuse supernova and solar neutrinos), particle physics (search for proton decay), and geophysics (geoneutrinos). LENA is a part of the European LAGUNA (Large Apparatus for Grand Unification and Neutrino Physics) collaboration that has been founded in order to study the feasibility of large-scale detectors with a common physics program. Apart from the liquid-scintillator detector LENA, it involves a 0.5 Mt water Cherenkov detector (MEMPHYS) and a 100 kt liquid Argon time projection chamber (GLACIER). The main part of the talk will be an overview of the physics potential of the LENA detector. The current technical feasibility studies concerning optical properties of liquid scintillator will be presented as well. In addition, some brief information about the current status of LENA and LAGUNA will be reported.
• Tuesday 26 February 2008 at 15.15 in A315: Kazunori Nakayama (ICRR, University of Tokyo) [cosmo seminar]
Axion, Supersymmetry and Inflation
Abstract: We derive general constraints on supersymmetric extension of axion models, in particular paying careful attention to the cosmological effects of saxion, which is the scalar partner of the axion. It is found that for every mass range of the saxion from keV to TeV, stringent upper bound on the reheating temperature is imposed. Implications on inflation models are also discussed.
• Wednesday 27 February 2008 at 9.15 in A315: Toyokazu Sekiguchi (ICRR, University of Tokyo) [cosmo seminar]
Primordial helium abundance and effective number of neutrino species from CMB: current constraints and forecasts
Abstract: We present constraints on the primordial helium abundance and the effective number of neutrino species from recent CMB observations. The biggest advantage of constraints from CMB alone is these less suffer from astrophysical systematics/subtleties. We also forecast constraints from Planck survey and discuss how Y_p affects the determination of other cosmological parameters. We finally discuss the possible lowest reheating temperature.

• Tuesday 11 March 2008 at 10.15 in E204: Ahmed Ali (Desy)
Theoretical Interest in B-Meson Physics at the B Factories, Tevatron and the LHC
Abstract: We review the salient features of B-meson physics, with particular emphasis on the measurements carried out at the B-factories and Tevatron, and anticipations at the LHC. Theoretical progress in understanding the current measurements in the context of the Standard Model will be highlighted. Further details can be seen in a recent Preprint DESY 07-212 [arXiv:0712.1022 (hep-ph)].
• Friday 14 March at 14.15 in A315: Hannu Kurki-Suonio (Helsinki)
WMAP 5-year results
An overview on the cosmological implications of the 5-year WMAP data.

• Tuesday 18 March 2008 at 10.15 in E204: Thorsten Battefeld (Princeton)
Non-Gaussianities in Multi-Field Inflation
Abstract: We consider non-Gaussianities in inflationary models with multiple, uncoupled scalar fields, incorporating models of assisted inflation, such as N-flation, where inflation is driven by multiple axion fields. After estimating parameters characterizing the bi- and trispectrum in the horizon crossing approximation, we turn our attention to the non-linearity parameter measuring the bispectrum; focussing on N-flation, we compute its magnitude for narrow and broad spreads of masses, including the evolution of modes after horizon crossing. We identify additional contributions due to said evolution and show that they are suppressed as long as the fields are evolving slowly. This renders N-flation indistinguishable from simple single-field models in this regime. We conclude with a summary of the many further developments that occurred over the last year. Relevant papers are hep-th/0703012 and astro-ph/0610296.
• Tuesday 25 March 2008 at 10.15 in E204: Andrew Lytle (University of Washington)
Nonperturbative Renormalization Using Staggered Quarks
Abstract: Accurate results in QCD using lattice simulations require matching factors between lattice and continuum operators. By imposing renormalization conditions directly on the lattice, one hopes to avoid the uncertainties from using lattice perturbation theory and ultimately improve the precision of current calculations. I will discuss the ongoing research I have been doing along these lines using staggered quarks.
• Tuesday 15 April 2008 at 10.15 in E204: Sami Nurmi (Helsinki, GRASPANP fellow)
Inflation in the Minimal supersymmetric standard model
Abstract: Recently it has been shown that flat directions of the MSSM can successfully act as the inflaton field [hep-ph/0605035]. I discuss the supergravity embedding of the model and show that the required extremely flat inflaton potential is a natural outcome in a class of supergravity models [0706.2355, 0710.1613].
• Tuesday 22 April 2008 at 10.15 in E204: Matti Krusius (Low temperature laboratory, Otaniemi)
Condensed matter hype: Cosmic strings from brane annihilations?
A recent superfluid helium experiment at the University of Lancaster UK raised concern and criticism around the question whether a condensed matter measurement can be used to learn about the early universe. The first step was to stabilize two coherent macroscopic quantum phases in a strongly configured magnetic field distribution. Next by sweeping rapidly down the field, one of the phases was forced to vanish, whereby the interfaces separating the shrinking phase from the surrounding growing phase annihilated. As a final step, a measurement was performed which showed that the annihilation process had left behind topological defects (although their structure cold not be identified). Two similar experiments from the Low Temperature Laboratory in Otaniemi (but involving entirely different measuring setups and methods) support the Lancaster conclusions (although a perfectly matching test has not been performed). What are the implications and their applicability – these are the questions which have raised the discussion.
• Tuesday 29 April 2008 at 10.15 in E204: Stanley J. Brodsky (SLAC, Stanford)
• Friday 9 May 2008 at 14.15 in A315: Syksy Räsänen (U. of Geneva)
The effect of structure formation on the expansion of the universe
I will discuss recent progress on explaining the late-time acceleration in the expansion of the universe via the effect of structure formation, without the need to introduce dark energy or modified gravity. One of the main results is that a preferred time of 10-100 billion years for the change in the expansion rate emerges from the cold dark matter transfer function without new free parameters.
• Thursday 15 May 2008 at 10.15 in A315: Simon Kwan (Fermilab)
CMS Tracker and the upgrade plan
The CMS detector is almost completely installed. This talk will focus primarily on the tracker, in particular the pixel detector. After describing the design, its current status, and expected performance, some preliminary thoughts on the upgrade plan of the pixel detector for the SLHC will be presented.
• Thursday 15 May 2008 at 14.15 in A315: Simon Hands (Swansea)
Two Color Matters
• Friday 16 May 2008 at 15.15 in A315: Vishnu Jejjala (IHES)
SQCD: A Geometric Aperçu
We take new algebraic and geometric perspectives on the old subject of SQCD. We count chiral gauge invariant operators using generating functions, or Hilbert series, derived from the plethystic programme and the Molien-Weyl formula. Using the character expansion technique, we examine how global symmetries are encoded in the generating functions. Equipped with these methods and the techniques of algorithmic algebraic geometry, we obtain character expansions for theories with arbitrary numbers of colours and flavours. Computational algebraic geometry allows us then to systematically study the classical vacuum moduli space of SQCD and investigate such structures as its irreducible components, degree, and syzygies. We find the vacuum manifolds of SQCD are affine Calabi-Yau cones over weighted projective varieties.
• Tuesday 20 May 2008 at 10.15 in E204: Finn Larsen (U. of Michigan and CERN)
The non-supersymmetric black holes in four dimensions
Extremal black holes with supersymmetry have been extensively studied. Those without supersymmetry have some similarities but also some qualitative differences. We construct these black holes explicitly and discuss their physical properties.
• Thursday 22 May 2008 at 10.15 in A315: Robert G. Leigh (U. of Illinois at Urbana-Champaign)
Mottness and Strong Coupling
I review the determination of a low energy theory of the Hubbard model, which models materials that exhibit superconductivity with high critical temperatures. One of the key features of this theory is the emergence of a collective degree of freedom that gives rise to many of the exotic phenomena associated with these materials. I motivate the appearance of this new degree of freedom, and derive it from the Hubbard model.
• Monday 26 May 2008 at 14.15 in A315: Kumar Ghosh (Ahmedabad, India)
Unparticles and some collider related phenomenology
The existence of an exactly scale invariant sector possessing a non-trivial infrared fixed point at a higher energy scale and its possible communication with the Standard Model particles through a heavy messenger sector has been shown to lead to curious unparticle effects at the low energy. Interaction of unparticles with the SM fields lead to several interesting phenomenological implications. In this talk I will mainly focus on effect of unparticles on muon decay and top pair production at the Tevatron as well as forthcoming LHC.
• Thursday 29 May 2008 at 10.15 in A315: Patta Yogendran (Hanyang U. and CQUeST)
“Winding” Strings in the 2-D Lorentzian black hole
We will discuss the spectrum of strings on the 2-D Lorentzian black hole. We will argue that the states of this theory are labelled by a parameter that arises from spectral flow. We will also demonstrate that states localized around the horizon exist and that these must also be included in the spectrum.
• Monday 2 June 2008 at 10.15 in A315: Aleksi Vuorinen (CERN)
I will review an AdS/CFT calculation of the energy spectrum of heavy-light mesons in N = 4 SU(N) super Yang-Mills theory with two massive N=2 hypermultiplets. I will discuss the fact that — contrary to existing studies — our results exhibit excitation energies independent of the heavy quark mass, and make some comments about related AdS/CFT models of flavor with less supersymmetry. The latter are expected to exhibit hyperfine mass splittings as well.
• Tuesday 3 June 2008 at 10.15 in A315: Carl E. Carlson (The College of William & Mary in Virginia)
Gravitational Form Factors of Mesons in an AdS/QCD Model
We will show how to calculate form factors using a holographic model of QCD, mainly discussing vector, axial, and pseudoscalar mesons. We will illustrate the techniques on gravitational form factors (which are useful for constraining the generalized parton distributions) as well as quoting the results for electromagnetic form factors. One striking outcome, comparing the several types of calculated form factors, is that mesons appear noticeably more compact when measured by the gravitational form factors than when measured by the charge form factor.
• Tuesday 17 June 2008 at 10.15 in A315: Duccio Abbaneo (CERN)
LHC and its detectors: the frontier of particle physics
The analysis of the data collected over more than a decade at the LEP collider deeply changed our understanding of the fundamental laws of Nature, demonstrating that the “Standard Model” describes fundamental particles and their interactions with a great level of accuracy. However, the Standard Model also leaves several primordial questions unanswered; making further progress entails the construction of exceptionally challenging experimental devices. The Large Hadron Collider and its giant detectors are about to start operation at the CERN laboratory: arguably one of the most exciting times ever, for fundamental research.
The seminar is intended to be a general colloquium.
• Wednesday 18 June 2008 at 14.15 in A315: Tomo Takahashi (Saga University) [cosmo seminar]
Non-Gaussianity in models with mixed inflaton and curvaton
Abstract: We study non-Gaussianity, the spectral index of primordial scalar fluctuations and tensor modes in models where fluctuations from the inflaton and the curvaton can both contribute to the present cosmic density fluctuations. Even though simple single-field inflation models generate only tiny non-Gaussianity, if we consider such a mixed scenario, large non-Gaussianity can be produced. Furthermore, we study the inflationary parameters such as the spectral index and the tensor-to-scalar ratio in this kind of models and discuss in what cases models predict the spectral index and tensor modes allowed by the current data while generating large non-Gaussianity, which may have many implications for model-buildings of the inflationary universe.
• Tuesday 24 June 2008 at 10.15 in A315: Esko Keski-Vakkuri (FL and HIP)
(QHE = Quantum Hall Effect)
• Wednesday 2 July 2008 at 14.15 in A315: Seiji Terashima (Kyoto)
On membrane actions
• Friday 8 August 2008 at 14.15 in A315: Thorsten Battefeld (Princeton University) [cosmo seminar]
Staggered Multi-Field Inflation
Abstract: We investigate multi-field inflationary scenarios with fields that drop out of the model in a staggered fashion. This feature is natural in certain multi-field inflationary setups within string theory; for instance, it can manifest itself when fields are related to tachyons that condense, or inter-brane distances that become meaningless when branes annihilate. Considering a separable potential, and promoting the number of fields to a smooth time-dependent function, we derive the formalism to deal with these models at the background and perturbed level, providing general expressions for the scalar spectral index and the running. We recover known results of e.g. a dynamically relaxing cosmological constant in the appropriate limits. We further show that isocurvature perturbations are suppressed during inflation, so that perturbations are adiabatic and nearly Gaussian. The resulting setup might be interpreted as a novel type of warm inflation, readily implemented within string theory and without many of the shortcomings associated with warm inflation. To exemplify the applicability of the formalism we consider three concrete models: assisted inflation with exponential potentials as a simple toy model (a graceful exit becomes possible), inflation from multiple tachyons (a constant decay rate of the number of fields and negligible slow roll contributions turns out to be in good agreement with observations) and inflation from multiple M5-branes within M-theory (a narrow stacking of branes yields a consistent scenario).

• Wednesday 13 August 2008 at 14.15 in A315: Anders Tranberg (University of Oulu) [cosmo seminar]
Doing it anyway: Quantum field thermalization in an expanding background
Abstract: The dynamics of quantum fields in and out of equilibrium is well described in the 2PI formalism, where equations for the full quantum field correlators can be derived and solved numerically. A number of practical issues need to be resolved when applying the formalism to the expanding early Universe, issues which may seem to make such an extension fruitless or even irrelevant. I will do it anyway, and solve the resulting equations for a number of cosmological phenomena, including thermalization and reheating. Remnants of the issues persist, imposing some simple and but not too restrictive rules about what can and cannot be done

• Tuesday 9 September 2008 at 10.15 in E204: Sourov Roy (IACS, Kolkata)
Neutrino masses and mixing in a TeV scale SUSY seesaw model
Abstract: We examine in detail the neutrino masses and mixing patterns in an extension of the minimal supersymmetric standard model with three gauge-singlet neutrinos and R-parity violation. The Majorana masses for the gauge-singlet neutrinos as well as the usual $\mu$-term for the Higgs superfields are generated at the electroweak scale through the vacuum expectation values of the singlet sneutrinos. The resulting effective mass matrix for the three light neutrinos have contributions from the seesaw mechanism involving the singlet neutrinos, as well as due to the mixing with the heavy neutralinos. We show that even with flavour diagonal neutrino Yukawa couplings, the global data on three-flavour neutrinos can be well accounted for in this scenario at the tree level. We also analyze the mixing in the chargino and the Higgs sector and calculate the decays of the lightest supersymmetric particle in this model. Some other phenomenological implications of such a model will be discussed.
• Thursday 18 September 2008 at 10.15 in A315: M. Shifman (William I. Fine Theoretical Physics Institute, University of Minnesota)
Supersymmetry and how it helps us understand strong interactions
Abstract: I review recent developments in supersymmetric non-Abelian gauge theories such as non-Abelian strings (flux tubes), confined monopoles and other elements of a big picture of the dual non-Abelian Meissner effect which is beginning to emerge. Its relevance to non-supersymmetric QCD-like theories is discussed.
• Tuesday 23 September 2008 at 10.15 in E204: Sami Saxell (FL)
On general properties of Lorentz-invariant formulation of noncommutative quantum field theory
Abstract: We study general properties of certain Lorentz-invariant noncommutative quantum field theories proposed in the literature. We show that causality in those theories does not hold, in contrast to the canonical noncommutative field theory with the light-wedge causality condition. This is the consequence of the infinite nonlocality of the theory getting spread in all spacetime directions. We also show that the time-ordered perturbation theory arising from the Hamiltonian formulation of noncommutative quantum field theories remains inequivalent to the covariant perturbation theory with usual Feynman rules even after restoration of Lorentz symmetry.
• Monday 29 September 2008 at 10.15 in HIP Coffee Room: Antti Niemi (Department of Theoretical Physics, Uppsala University and Laboratoire de Mathématiques et Physique Théorique, Université de Tours and Chern Institute of Mathematics, Nankai University, Tianjin))
Gauge theory approach to protein folding landscape
• Tuesday 30 September 2008 at 10.15 in E204: Tomi Paananen (FL)
Superfluid Fermi gas in optical lattices
Abstract: We study an ultracold two-component Fermi gas in optical lattices and predict the existence of several different superfluid phases, namely the FFLO, BP, and the standard BCS phases, as well as different phase separations. Our main result is that FFLO exists in a large part of the temperature-polarization phase diagram. We calculate the superfluid density of the Fermi gas in optical lattices and show that the different phases can be differentiate from each other by using superfluid densities. We also calculate the superfluid density of the strongly polarized Fermi gas in the case when exited p-bands are populated.
• Tuesday 14 October 2008 at 10.15 in E204: Keijo Hämäläinen (FL)
From pictures to movies – in situ studies of structural dynamics with future radiation sources
Abstract: Macroscopic properties of materials rely on the underlying electronic structure. During the last decade the structural studies have been revolutionalized due to the advent of the third generation synchrotron x-ray sources. In the presentation the very recent and prospected future evolution from static structure determination to dynamics at all length and times scales are reviewed.
• Tuesday 28 October 2008 at 10.15 in E204: Tomislav Prokopec (Utrecht University)
Cosmological constant and quantum backreaction
Abstract: A decade ago it was discovered that at the largest scales the Universe’s dynamics is governed by a substance with properties of a cosmological constant, which has come to be known as dark energy. I will overview what have we in the meantime learned about the properties of this mysterious substance. I will then discuss our progress in understanding the quantum backreaction of gravitons and matter fields in cosmological spacetimes.
• Tuesday 11 November 2008 at 10.15 in E204: Anirban Kundu (University of Calcutta, Kolkata, India)
Universal Extra Dimensions
Abstract: I will talk about the formalism and phenomenology of the Universal Extra Dimension model, where all Standard Model fields are free to propagate in the extra compactified dimensions. The low-energy and collider phenomenology of the minimal version of UED will be discussed. In particular, I will show how this model can be discriminated from other new physics models like supersymmetry, notwithstanding the fact that the full spectrum of this model is extremely challenging to detect at the LHC.
• Tuesday 18 November 2008 at 10.15 in E204: Koji Hashimoto (RIKEN)
Toward a proof of Montonen-Olive duality via multiple M2-branes
Abstract: We derive 4-dimensional N=4 U(N) supersymmetric Yang-Mills theory from a 3-dimensional Chern-Simons-matter theory with product gauge group U(N)^(2n). The latter describes M2-branes probing an orbifold where a torus emerges in a scaling limit. Starting from one single Chern-Simons-matter theory, we find infinitely many equivalent 4-dimensional theories differing up to an SL(2,Z) redefinition of the gauge coupling tau (= theta/2pi + 4pi i/g^2). This would provide a proof of the Montonen-Olive duality. However, because our tau is not generic, the S-transformation (tau -> -1/tau) can be thought of as a parity transformation in 4 dimensions.
• Tuesday 25 November 2008 at 10.15 in E204: Kimmo Tuominen (Jyväskylä and HIP)
Walking Technicolor on the lattice
Abstract: Conformal quantum field theories are of interest for Beyond the Standard Model physics concerning e.g. unparticles and Technicolor. Current experimental data indicate that in phenomenologically viable Technicolor models the coupling must walk: from asymptotic freedom at short distances the coupling approaches a quasi-stable Wilson-Fisher fixed point and “walks” over a large scale separation, but is ultimately driven away from it due to a relevant perturbation leading to confinement at long distances. We have proposed a specific gauge theory which would have a nontrivial infrared fixed point, and as such could serve as an important concrete resource for model building. We have performed extensive numerical Monte Carlo simulations which indicate that the proposed theory is exactly or almost conformal.
• Tuesday 2 December 2008 at 10.15 in E204: Lotta Mether (HIP)
Leptogenesis: the correct way of creating the net baryon number of the Universe?
Abstract: TBA
• Tuesday 9 December 2008 at 10.15 in E204: Esko Keski-Vakkuri (FL and HIP)
Issues of string theory
Abstract: I will review some questions that motivated the birth of string theory, introduce some of its key features and achievements, and discuss some promising directions for its future. This is an introductory talk, unlike a regular seminar.–>
• Tuesday 16 December 2008 at 14.15 in A315: Mauri Valtonen (University of Turku)
Note time and place!
Tests of general relativity under strong fields
Abstract: General Relativity has been tested in several ways since 1915 when Einstein published his theory. The theory proposes that gravitation is a manifestation of curvature of space. The tests of the theory include the precession of the orbit of Mercury and bending of starlight when passing close to the sun. However, all the tests so far are weak field tests. The best case for the study of the strong gravitational fields may be a close binary black hole system, and the best known candidate of such systems is OJ287 which was discovered by my research group as a periodically varying system in 1980.s. Based on the light curve, Sillanpää, Haarala, Valtonen, Sundelius & Byrd 1988 (ApJ 325, 628) proposed that the outburst phases repeated at approximately 12 year intervals are generated by a binary black hole system in an eccentric orbit. A close approach of two black holes was thought to activate the jet emission from one of the components by increasing accretion flow tidally. Lehto and Valtonen (1996, ApJ 460, 207) improved on this model by including the direct effects of the secondary black hole on the accretion disk of the primary.
The advantage of this model is that it is possible to calculate a unique solution of the orbit as soon as six flares arising from the disk crossing have been observed. The solution became possible for the first time after the 2005 flare (Valtonen 2007, ApJ 659, 1074, http://adsabs.harvard.edu/abs/2007ApJ…659.1074V). The solution explains all the past flares in the historical light curve, as well as predicts all future flares. The only remaining free parameter was the rate of energy loss of the binary orbit: if the rate follows Einstein.s theory, the next expected flare was at September 13, 2007. In case the orbital period stays constant, the next flare was expected 20 days later.
Now the answer is known: The next flare started at September 12.3, i.e. 16 hours earlier than predicted. The outburst was as predicted also in other respects: the outburst profile, excluding the random variations on top the outburst light, was as calculated 12 years earlier. The basic binary model of Sillanpää, Lehto, Sundelius et al. can now be viewed as confirmed. In future research one of the interesting problems is to improve the accuracy of the orbital elements of the binary in order to verify the level of energy loss to gravitational radiation. The 2007 prediction was correct at the level of 0.7 days out of 20 days, i.e. 3.5 %. The theory predicts that there should have been 21 flares in 1891-2007: if they are all observed even at lower resolution, the model becomes very much overdetermined, and the level of the test of General Relativity should be possible at 1% level. So what should be done to achieve this goal? First, the study of historical plate archives should continue. The second important project is the improvement of the computer code which solves the orbit. A third area of research concerns with the details of astrophysical processes that produce radiation during the outburst. Of special interest are radio observations where it is possible to see the jet of the source.