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## Seminars Archive

2007  2008  2009  2010  2011  2012  2013  2014  2015  2016  2017
8 Dec 2009
15:00
Lev VidmarMagnetic-lattice polaron and bipolaron in the cuprates
V seminarski sobi odsekov za fiziko (106)

Charge carriers moving in the magnetic background are the central focus of many microscopic models relevant to describe the properties of cuprate superconductors. Recently, growing evidence is emerging in favor of significance of lattice degrees of freedom in underdoped cuprates. We explore the interplay between strong correlations and lattice degrees of freedom in the limit of one and two doped charge carriers, which lead to formation of a magnetic-lattice polaron and bipolaron.
I will review some results of the magnetic-lattice polaron properties, as described by the t-J Holstein model, and introduce a more realistic model for description of the magnetic-lattice bipolaron. I will show how two different polarizations of quantum oxygen vibrations influence the spacial symmetry of the bound magnetic bipolaron in the context of the t-J model. Linear as well as quadratic electron-phonon coupling to transverse polarization stabilize d-wave symmetry, where the existence of a magnetic background is essential for the formation of a d-wave bipolaron state. On the other hand, with increasing linear electron-phonon coupling to longitudinal polarization the symmetry of a d-wave bipolaron state changes to p wave.

24 Nov 2009
15:00
Ana HocevarMorphometry and structure of natural random tilings
V seminarski sobi odekov za fiziko (106).

To better understand the observed universality of their structure, we analyze the morphometry of a set of living and inanimate planar cellular partitions. We characterize them by the distributions of polygon reduced area, a scale-free measure of the roundedness of polygons. These distributions are fairly sharp and seem to belong to the same family. By comparing the frequencies of the polygon classes, we map all samples onto model tilings of equal-area, equal-perimeter polygons. We argue that the random two-dimensional patterns can be parametrized by their median reduced area alone.

17 Nov 2009
15:00
Prof. Vyatcheslav B. PriezzhevLogarithmic Correlations in Lattice Models
V seminarski sobi odsekov za fiziko (106).

Two-point correlation functions of free-fermion models on the 2D lattice are considered at the critical point. An origin of logarithmic corrections to power laws is analysed. A crucial role of non-local diagrams is revealed and illustrated by examples for the Abelian sandpile model. Obtained results are compared with predictions of the logarithmic conformal field theory (LCFT).

3 Nov 2009
15:00
Anze Losdorfer BozicPok nabite, prazne virusne kapside
V seminarski sobi odsekov za fiziko (106).
Po kratkem uvodu v biofiziko virusov bom predstavil preprost model poka nabite virusne kapside, ki se nahaja v solni raztopini ob odsotnosti virusnega genoma. Elektrostatski odboj med naboji na posameznih proteinskih gradnikih tezi k tvorbi odprtin, docim se s pokom elektrolitu izpostavi rob kapside, kar je za gradnike energetsko manj ugodno. Poceno kapsido aproksimiramo kot enakomerno nabito sfericno kapico, katere elektrostatsko prosto energijo racunamo v Poisson-Boltzmannovem priblizku povprecnega polja, temu pa pridodamo se energijo linijske napetosti izpostavljenega roba. Termodinamska stabilnost sistema je tako odvisna od medsebojnega vpliva obeh prispevkov. Model poleg tega omogoca tudi analizo razpada dveh vrst membran: fleksibilnih membran (npr. kapsid), kjer se membrana razdeli na dva kosa, ter tekocih membran (npr. vesiklov), kjer tvorba odprtine poteka brez izgube materiala.

13 Oct 2009
15:00
Prof. Thomas Pruschke
University of Goettingen, Germany
Competing interactions and magnetic order in correlated electron systems
In physics seminar room (106).

8 Oct 2009
15:00
Wataru Koshibae
ASI, RIKEN, Wako, Saitama, Japan
Relaxation dynamics of excited states in the spin-electron coupled systems
In physics seminar rook (106)
The anomalous and large cross-effect between electronic transport and the external field is nothing more than the control of the excited electronic states and its relaxation by the external field. In the unconventional electron systems, highly non-trivial relaxation process of the non-equilibrium states is expected. We have studied numerically the relaxation process in the spin-electron coupled systems. We study quantum dynamics of the excited electronic states in the double-exchange model at half-filling by solving coupled equations for the quantum evolution of electrons and Landau-Lifshits-Gilbert equation for classical spins. The localized spin is considered to be a classical vector with a magnitude S. The ground state of the double-exchange model at half filling is the antiferromagnetic insulating state because of the perfect nesting-condition in this system. Using finite size systems, we numerically investigate the relaxation dynamics of excited states by calculating time evolution of the electronic states and local spin structure. We find that the time scale of the relaxation dynamics is fairly longer than the inverse of the kinetic energy and interactions of electrons, and the spatial inhomogeneity plays crucial roles. In particular, the inter-band relaxation occurs through the in-gap state localized near the large spin tilting from the ground state antiferromagnetic configuration, and we find the non-adiabatic quantum transitions through a resonant mutual precession analogous to the electron spin resonance (ESR) process. Sensitivity of the quantum dynamics on the parameters in the model is also investigated .

6 Oct 2009
15:00
Hiroaki Matsueda
Sendai National College of Technology, Japan
Time-dependent DMRG study of relaxation dynamics in photoexcited one-dimensional Mott insulator
In physics seminar room (106)
Strongly correlated electron systems exhibit peculiar optical properties that are promising for future optoelectronic devises. One of long-standing problems is seen in one-dimensional Mott insulators, and the problem is how to understand photoinduced insulator-to-metal transition accompanied with its picosecond recovery to the insulating ground state. Spin and phonon relaxations are two possible candidates. We calculate time dependence of the photocarrier number, the phonon number, and the spin energy after photoexcitation in the Hubbard-Holstein model with vector potential of pulsed laser light. Various DMRG methods are combined for these calculations. In the absence of the electron-phonon coupling, the spin relaxation is not efficient even for the strong pulse that would break the spin-charge separation. In the presence of the electron-phonon coupling, the energy absorption of phonons are dramatically even for small electron-phonon coupling, while the spin relaxation is much more suppressed. In addition to the photoinduced dynamics, I am also going to present recent development of time-dependent DMRG and related methods.

27 Aug 2009
12:00
Ilja Doršner, Svjetlana FajferOmejitve na leptokvarke iz fizike nizkih energij
In the tea room of F-1 department. more...

30 Jul 2009
12:00
Gorazd Cvetič (Univ. Tecnica Federico St. Maria, Valparaiso)Analitična QCD
In the tea room of F-1 department. more...

24 Jul 2009
11:00
Jelena Zivkovic, Radboud University, NijmegenDynamic Force Spectroscopy on RNA-Protein Complex, Data and Statistical Analysis
Seminar will be at 11:15 in TEA ROOM of F1 Department

16 Jul 2009
12:00
Veljko Dmitrasinovic (Vinca Institute of Nuclear Sciences)A variational estimate of the Higgs mass
In the tea room of F-1 departement.

In view of the impending restart of LHC I offer a reminder of the 2.2 TeV calculation/prediction of the Higgs mass in the Standard Model based on the Gaussian functional variational approximation, by R. Ibanez-Meier, I. Stancu and P.M. Stevenson. Z.Phys. C70, 307 (1996). I show proofs of the gauge invariance (V.D., Nuov. Cim. 109A, 1187 (1996)) and of the unitarity and causality of this calculation (I. Nakamura and V.D., Nucl. Phys. A713, 133, 2003)). more...

9 Jul 2009
12:00
Wei Liao (East China University of Science and Technology)Equations and flavor transformation of neutrinos in supernova
In the tea room of F-1 department.

We derive a series of moment equations describing the motion and flavor transformation of neutrinos in supernova. We find a particular series of moments of neutrino density matrix in supernova. The emission angle distribution of neutrinos is described by this series of moments. We expand the equation of neutrinos using these moments and obtain moment equations. We find that these moments have very good property of convergence and the infinite series of equations can be truncated to equations with a small set of moments. Using a small set of moment equations the required computational power is reduced by about two orders of magnitude compared to that in multi-angle simulation. The study on non-linear flavor transformation of neutrinos is substantially simplified using these equations. Two flavor system of neutrinos is also considered and new equations describing the flavor polarization vectors of neutrinos are found. more...

30 Jun 2009
12:00
Manimala MitraType-III Seesaw with 2HDM
In the tea room of F1 department.

Proof of neutrino masses and mixing from a series of outstanding experimental efforts have opened a window to physics beyond the standard model of particle physics. There must be some underlying theory which explains the very particular neutrino mass difference and mixing. It is well known that Seesaw mechanism has its success in explaining the smallness of neutrino mass. While many works have been recently done in the context of Type-III Seesaw which requires a fermionic triplet, we have concentrated on Type-III Seesaw in the presence of an additional Higgs doublet and on $\\mu-\\tau$ symmetry. In this context we have studied the phenomenological predictions and the model signatures which Type-III Seesaw with 2HDM offers. more...

23 Jun 2009
15:00
G. J. Rodgers
Brunel University, United Kingdom
Statistical physics and healthcare systems
V seminarski sobi odsekov za fiziko (106)
I present two applications of statistical physics to problems in the provision of healthcare. In the first I present an analysis of one years\' worth of empirical data on the arrival and discharge times at a UK Accident and Emergency (A\\&E) department. I find that discharges rates vary slightly with the workload, that the distribution of the length of stay has a fat tail and that a sand pile model mimics the qualitative behaviour of the system. In the second application the distribution of patients\' lengths of stay in English hospitals is measured by using routinely collected data from 11 years. It is found to be well approximated by a power-law distribution spanning over more than 3 decades. To explain this observation, a theoretical resource allocation model is presented.

4 Jun 2009
12:00
Jernej Fesel KamenikSignatures of Heavy Vectors in Higgsless models
In the tea room of F-1 department.

One or more heavy spin-1 fields may replace the Higgs boson in keeping perturbative unitarity up to a few TeV while at the same time account for the ElectroWeak Precision Tests. We study the Drell-Yan production of heavy vector and axial-vector states of generic Higgsless models at hadron colliders. We analyse in particular the l+l-, WZ, and three SM gauge boson final states. In the l+l- case we show how present Tevatron data restricts the allowed parameter space of these models. The two and three gauge boson final states (especially WZ, WWZ, and WZZ) are particularly interesting in view of the LHC, especially for light axial-vector masses, and could shed more light on the role of spin-1 resonances in the electroweak precision tests. more...

28 May 2009
12:45
Jonathan Rocher (ULB Brussels)Challenges for hybrid inflation: SUSY GUTs, spectral index and initial conditions

Now that CMB observational data increased in precision, the question of which (class of) models are the best candidates to realize inflation is particularly urging. Hybrid inflation is one of the three main classes of inflationary models and is considered very motivated among high energy physicists. After a quick review about hybrid inflation and the reasons why it is popular in the high energy community, I will discuss the phenomenology of these models and the challenges they have to face. I will first review some consequences of embedding it in SUSY GUTs : the difficulty to find an inflaton candidate and the constraints imposed by the formation of cosmic strings. I will then turn to two of its main problems: the blue spectral index in disagreement with WMAP5 and the space of initial conditions for inflation to be successful. I will show that the slow roll approximation should not always be trusted to study the model, and discuss what we learn from the exact dynamics in terms of spectral index and ways to realize hybrid inflation. We have used numerical resolution of the dynamics to understand and study the properties of the initial condition space available for successful inflation. I will show that both problems mentioned above can be avoided by considering superplanckian initial values for the fields and discuss the consequences for the models.

Based on arXiv:0809.4355, hep-ph/0406120, hep-ph/0308134 as well as work in progress : A. Mazumdar, J. Rocher, \ more...

21 May 2009
13:00
Bojan GolliUganke Roperjeve resonance
In the IJS seminar room (n. 106). more...

20 May 2009
13:00
prof. dr. Sergei Kruchinin
BITP, Kiev, Ukraine
Thermoelectricity in double-barrier structure with resonant tunneling
V seminarski sobi odsekov za fiziko (106)

19 May 2009
15:00
dr. Jernej MravljeVpliv fononv na Kondov pojav v nanoskopskih sistemih
V seminarski sobi odsekov za fiziko (106)
Kvantne pike in molekularni mosticki predstavljajo nanoskopske realizacije Andersonovega modela magnetnih necistoc. Prevodnost teh sistemov pri nizkih temperaturah je namrec ojacana zaradi Kondovega pojava. V molekularnih mostickih je poleg Coulombskega odboja pomembna tudi sklopitev na fonone dveh tipov: na molekularna lastna nihanja in na oscilacije molekul med kontakti. Medtem ko vpliv prvih lahko opisemo z renormalizacijo parametrov modela, drugi sklapljajo molekulo na dodatni prevodni kanal, kar lahko vodi do kvalitativno drugacnega obnasanja. V seminarju bom predstavil analiticne in numericne rezultate v modelih za fonone obeh tipov.

14 May 2009
12:00
Eung Jin Chun (KIAS, Seul, Korea)LFV and leptogenesis in Higgs exampt no-scale supergravity
In the IJS seminar room (n. 106) more...

12 May 2009
15:00
dr. Jorgen Rammer
Inst. of Phys., Umea University, Sweden
Counting statistics of interfering Bose-Einstein condensates
In Physics seminar room (106).

7 May 2009
15:00
prof. dr. Roberto Serra
Modena and Reggio Emilia University
Synchronization in protocell models
In physics seminar room (106)
Protocells are lipid vesicles (or, less frequently) micelles which are endowed with some rudimentary metabolism and contain {\\it genetic} material, and which should be able to grow, reproduce and evolve. While viable protocells do not yet exist, their study is important in order to understand possible scenarios for the origin of life, as well as for creating new {\\it protolife} forms which are able to adapt and evolve. This endeavour has an obvious theoretical interest, but it might also lead to an entirely new {\\it living technology}, definitely different from conventional biotechnology. Theoretical models can be extremely useful to devise possible protocell architectures and to forecast their behaviour. In this talk I will address an important issue in protocell research. What can be called the {\\it genetic material} of a protocell is composed by a set of molecules which, collectively, are able to replicate themselves. At the same time, the whole protocell undergoes a growth process (its metabolism) followed by a breakup into two daughter cells. This breakup is a physical phenomenon which is frequently observed in lipid vesicles, and it has nothing to do with life, although it superficially resembles the division of a cell. In order for evolution to be possible, some genetic molecules should affect the rate of duplication of the whole container, and some mechanisms have been proposed whereby this can be achieved.

23 Apr 2009
12:00
Matej PavsicO posplositvi prostora-casa: teorija relativnosti v konfiguracijskem prostoru
In the tea room of F-1 departmet. more...

17 Apr 2009
11:00
Jure ZupanGeneral Minimal Flavor Mediation
In the tea room of F-1 department. more...

31 Mar 2009
15:00
Jun-ichi Fukuda, (AIST, Japonska)Theory and simulation of liquid crystal anchoring on a grooved surface
Location: Physics seminar room (106)

Surface anchoring is a tendency of liquid crystal molecules to align along some specific direction with respect to a confining surface. The understanding of the origin and mechanism of surface anchoring is an important subject of liquid crystal science.
In 1972, Berreman proposed a theory of surface anchoring induced by a microscopically grooved surface[1]. His theory is based on an idea that liquid crystal molecules tend to align along the groove direction to minimize the elastic energy of the liquid crystal distortions. The deviation of the average orientation of liquid crystals from the groove direction costs energy, which is the origin of the surface anchoriqng energy. His theory, although simple enough, has been regarded as capturing the essence of surface anchoring and widely accepted in the field. However, his theory was criticized very recently[2], and it was revealed that his theory is based on an invalid assumption in the treatment of the liquid crystal distortions and cannot incorporate properly the contribution of so-called surfacelike elasticity.
In this talk, I will show how Berreman\'s theory should be modified and give the correct formula for the anchoring energy as a function of the average orientation of liquid crystals with respect to the groove direction. I will also argue that our theory is readily extended to surfaces with arbitrary groove patterns[3]. Furthermore, I will present some numerical attempts[4] to evaluate the anchoring energy and compare our numerical results with theory.
References:
[1] D.W. Berreman, Phys. Rev. Lett. 28, 1683 (1972); Mol. Cryst. Liq. Cryst. 23, 215 (1973).
[2] J. Fukuda, M. Yoneya and H. Yokoyama, Phys. Rev. Lett. 98, 187803 (2007); ibid. 99, 139902(Erratum) (2007).
[3] J. Fukuda, J.S. Gwag, M. Yoneya and H. Yokoyama, Phys. Rev. E 77, 011702 (2008).
[4] J. Fukuda, M. Yoneya and H. Yokoyama, Phys. Rev. E 77, 030701(R) (2008); ibid. 79, 011705 (2009)

12 Mar 2009
12:00
Ho-Ung Yee (ICTP)Holographic Monopole Catalysis of Baryon Decay
In the tea room of F-1 department. more...

10 Mar 2009
15:00
prof. Jan Forsman,
Chemical Center, Univer. of Lund, Sweden
Density functional theories of Coulomb fluids
In physics seminar room (106)
Most current density functional theories relies upon the presence of hard cores, also between ions of like charge. These hard cores should in principle reflect exchange repulsion. However, by the way in which these theories are formulated, the hard cores effectively determine the range of ion-ion correlations. In this talk, I will present alternative density functional theories to describe aqueous salt solutions. In these approaches, an approximation of the relevant {\\it Coulomb hole} that results from correlations between like-charged ions, is calculated (rather than chosen ad hoc) for the system under study.

5 Mar 2009
14:00
Michiyasu Mori,
Institute for Materials Research, Sendai
Electronic states of iron-based superconductors
Physics seminar room (106).
We will give a brief review on the iron-based superconductors, and remark some puzzles on superconductivity and antiferromagnetism in this compound. Electronic states will be discussed from viewpoint of material dependence. In this study, the band structure composed of Fe and As is calculated by the Slater and Koster\'s method to give hopping integrals of Fe-Fe and Fe-As bonds. It is found that the spectral weight near the Fermi energy is dominated by yz, zx and x2-y2 orbitals. Depending on materials, the most dominant orbital changes among these orbitals. In terms of crystal field, the yz and zx orbitals are higher in energy around the regular tetragonal of As, and superconducting critical temperature is maximum. On the other hand, yz and zx orbitals become lower in energy for a distorted tetragonal, in which the antiferromagnetic state occurs accompanied by structural change. Hence, such an orbital crossover must be crucial for the electronic states as superconductivity and antiferromagnetism. We will show some preliminary results by the Hartree-Fock calculation of multi-band Hubbard model.

26 Feb 2009
12:00
Jure DrobnakKratek pregled fizike top kvarka in predstavitev nase analize razpada t --> c l+l-
In the tea room of F1 department. more...

29 Jan 2009
12:00
Ivica Picek (Univ. of Zagreb)New TeV-scale Quark in Rare K and B Decays
In the tea room of F1 department.

It is conceivable that possible new quark states can be out of the direct LHC production reach, and that one could infer on them from their virtual loop effects. We introduce a secondary top state allowed by the existing electroweak precision tests. This state satisfies the requirements of small CKM unitarity violation and minimal flavour violation, and we examine its effects on selected rare K and B decays. It turns out that such rather heavy extra top has the best chance to be recovered via an increase in B_s -> mu^+ mu^- decay rate measured at the LHC. more...

22 Jan 2009
12:00
Lorenzo Calibbi (SISSA, Trieste)Gauge coupling unification with magic fields
In the tea room of F1 department.

We consider field sets that do not form complete SU(5) multiplets, but exactly preserve the one-loop MSSM prediction for alpha_3(M_Z) independently of the value of their mass. The unification scale is in general affected by such new fields and can be raised to larger values. These magic\'\' fields represent a useful tool in GUT model building: they can be used to fix gauge coupling unification in two-step breakings of the unified group, to suppress large KK thresholds in models with extra dimensions, or they can be interpreted as messengers of supersymmetry breaking in GMSB models. more...

20 Jan 2009
15:00
O. S. BarišićSingle static impurity in a Heisenberg chain
In physics seminar room (106).
The effect of a single static impurity on the many-body states and on the spin and thermal transport in the one dimensional anisotropic Heisenberg chain at finite temperatures is studied. Whereas due to integrability the pure Heisenberg model exhibits Poisson level statistics and dissipationless transport within the chain, it is found using the numerical approach that at least at high enough temperature a single impurity induces Wigner-Dyson level statistics and incoherent transport with a well defined current relaxation rate.

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