- 25.02.2010/12:00
Dl. Dorel Pietreanu (doctorand, conducator doctorat Dr. Mihai Visinescu)
Referate de doctorat:
- Studiul atomilor kaonici
- Experimentul SIDDHARTA: rezultate si performante
(Abstract)
Atomii kaonici fac parte din categoria atomilor exotici. Acestia se
formeaza atunci cand o particula incarcata negativ (pion, miuon, kaon )
înlocuieste unul din electronii de pe orbitele superioare ale atomului.
Atomii exotici sunt folositi ca instrument de studiu in mai multe
domenii ale fizicii, dintre care cele mai importante sunt studiul
interactiilor fundamentale (interactia tare in cazul atomilor hadronici )
si a simetriilor fundamentale (testarea CPT folosind heliul antiprotonic
si antihidrogenul). In particular studiul unui atom hadronic simplu (ex.
hidrogenul kaonic), permite o investigare directa a interactiei tari
antikaon-nucleon la energii joase. Desi in cazul acestui sistem
interactia fundamentala este cea electromagnetica, experimental se poate
observa o deplasare si o largire a nivelului energetic 1s datorate
interactiei tari precum si a timpului redus de viata al acestui atom
exotic.
In experimentul SIDDHARTA (Silicon Drift Detector for Hadronic Atom
Research by Timing Application) s-au studiat urmatoarele sistemele de
atomi exotici: hidrogenul, heliu si deuteriu kaonic (prima masuratoare din
lume). Vor fi prezentate rezultatele obtinute si implicatiile acestora.
Bibliografie:
- S. Okada, D. Pietreanu et al.,
"Precision measurement of the 3d---> 2p x-ray energy in kaonic He-4",
Phys. Lett. B653 (2007) 387
- V. Lucherini, D. Pietreanu et al.,
"Hadronic atoms physics at DAFNE",
Int. J. Mod. Phys. A22 (2007) 479
- T. Ishiwatari, D. Pietreanu et al.,
"Silicon Drift Detectors for the kaonic atoms X-ray measurements in
the SIDDHARTA experiment",
Nucl. Instrum. Meth., A581 (2007) 326
- M. Bazzi, D. Pietreanu et al.,
"Kaonic helium-4 X-ray measurement in SIDDHARTA",
Phys. Lett. B681 (2009) 310
- J. Zmeskal, D. Pietreanu et al.,
"Kaonic atoms at DAFNE: The SIDDHARTA experiment",
Int. J. Mod. Phys. A24 (2009) 190
- 18.02.2010/12:00
Dr. Mirela Babalic, DFT-IFIN
"Interactii
între colectii de câmpuri tensoriale nemasive cu simetriile mixte
(3,1) si (2,2)"
(Abstract)
Lucrand in ipotezele generale standard asupra deformarilor (localitate
spatio-temporala, analiticitate in constanta de cuplaj, covarianta
Lorentz, invarianta Poincaré si conservarea ordinului derivativ maxim al
ecuatiilor de camp pentru teoria cu interactie in raport cu cea libera)
investigam self-interactiile si cross-interactiile consistente intre doua
colectii de campuri tensoriale nemasive cu simetriile mixte (3,1) si
respectiv (2,2) folosindu-ne de teoria deformarilor bazata pe formalismul
BRST anticamp si de tehnici specifice de coomologie BRST locala.
Am obtinut ca: a) nu apar self-interactii care sa deformeze transformarile
gauge originale, b) apar cross-interactii consistente intre cele doua
colectii de campuri in ordinele unu si doi in constanta de cuplaj astfel
incat o parte din generatorii gauge si din functiile de reductibilitate
sufera deformari, c) existenta sau inexistenta cross-interactiilor intre
diferite campuri cu simetria mixta (2,2) depind de comportamentul
indefinit, sau respectiv pozitiv-definit al matricii tensorului metric
corespunzator.
- 11.02.2010/12:00
Dr. Dragos Anghel, DFT-IFIN
"Statistica de excluziune fractionara in sisteme de particule aflate in
interactie"
(Abstract)
Voi incepe prezentarea cu o scurta explicare a conceptului de statistica
fractionara, introdus de Haldane in Phys. Rev. Lett. 67, 937 (1991) si a
carui termodinamica a fost dedusa 3 ani mai tarziu, in mod independent,
de Yong-Shi Wu (Phys. Rev. Lett. 73, 922, 1994) si S. B. Isakov (Phys.
Rev. Lett. 73, 2150, 1994).
Pentru a arata utilitatea conceptului, voi discuta diverse sisteme de
particule aflate in interactie (de ex. modele 1D, de tip
Calogero-Sutherland, sau pe lichide Fermi) si voi arata cum se manifesta
statistica fractionara in aceste sisteme.
Folosind aceste exemple ca punct de plecare, voi demonstra unele
proprietati de baza, recent publicate, ale statisticii fractionare.
Bibliografie:
[1] D. V. Anghel, Comment on "Statistical Distribution for Generalized
Ideal Gas of Fractional-Statistics Particles", Phys. Rev. Lett. 73, 922
(1994), to appear in PRL.
[2] D. V. Anghel, The fractional exclusion statistics amended, EPL 87,
60009 (2009); arXiv:0906.4836.
[3] D. V. Anghel, Properties of fractional exclusion statistics in
interacting particle systems, Rom. J. Phys. 54, 281 (2009); arXiv:0804.1474.
[4] D. V. Anghel, Fractional exclusion statistics in general systems
with interaction, Phys. Lett. A 372, 5745 (2008); arXiv:0710.0728.
[5] D. V. Anghel, The thermodynamic limit for fractional exclusion
statistics, J. Phys. A: Math. Theor. 40 F1013-F1019 (2007); arXiv:0710.0724.
- 04.02.2010/12:00
Dr. Petre Dita, DFT-IFIN
"New Hadamard Matrices from Mutually Unbiased Bases"
[slides-pdf]
(Abstract)
An analytical method for getting new complex Hadamard matrices by
using mutually unbiased bases and doubling formulas is provided. The
method is illustrated with the n=4 case that lead to a rich family of
eight-dimensional Hadamard matrices depending on five arbitrary phases.
- 28.01.2010/12:00
Dr. Radu A. Gherghescu, DFT-IFIN
"Stable configurations of deposited atomic clusters"
(Abstract)
Deposited atomic cluster configurations are investigated under the
hypothesis of spheroidal cap shapes being a stable geometry as a
result of cluster-surface interaction. The macroscopic-microscopic
method is employed to calculate the deformation energy. A specialized
single-particle shell model (jellium type) is developed in order to
account for the quantum effects, and the liquid-drop approach is used to
calculate the macroscopic part of the energy. The minima within the
total deformation energy are interpreted as equilibrium states of atomic
clusters on surfaces. Calculations have been performed for the atom
numbers N=20, 70 and 200.
- 21.01.2010/12:00
Dr. Aurelian Isar, DFT-IFIN
"Entanglement dynamics of two-mode Gaussian states in a thermal
environment"
[slides-pdf]
(Abstract)
Within the framework of the theory of open systems based on
completely positive quantum dynamical semigroups, we give a description of the
continuous variable entanglement for a system consisting of two uncoupled modes
interacting with a thermal environment. Using the Peres–Simon
necessary and sufficient criterion for separability of two-mode Gaussian states, we
describe the generation and evolution of entanglement in terms of the covariance
matrix for a Gaussian input state. For some values of the temperature of
environment, the state keeps for all times its initial type — separable or
entangled. In other cases, entanglement generation, entanglement sudden death, or a
periodic collapse and revival of entanglement take place. We analyze also the time
evolution of the logarithmic negativity, which characterizes the degree of
entanglement of the quantum state.
- 14.01.2010/12:00
Dr. Lucia Popa, ISS
"Higgs mass from cosmological and astrophysical measurements" [arXiv:0910.5312]
(Abstract)
For the robust interpretation of the upcoming observations from Planck and
LHC experiments it is imperative to understand how the inflationary
dynamics of the Higgs scalar field may affect the inflationary observables.
I will present constraints on the inflationary observables and Higgs mass
boson obtained from the analysis of WMAP 5-year CMB measurements
complemented with geometric probes from supernovae and
baryon acoustic oscillations.
- 10.12.2009/12:00
dl Florian Catalin Popa (doctorand)-Institutul de Stiinte Spatiale
(Conducator Doctorat: Dr. Mihai Visinescu)
"Contributii la studiul gravitatiei cuantice (prezentararea rezultatelor din teza de doctorat)"
(Abstract)
Vor fi prezentate implicatiile existentei tensorilor Stackel-Killing si
Killing-Yano de rang arbitrar atat la nivel clasic cat si la nivel cuantic
in teoria gravitatiei.
Pentru o metrica data (Kimura IIC), vor fi prezentati, in mod explicit,
tensorii Killing-Yano de rang trei si tensorii Stackel-Killing asociati.
Se va arata ca intre cele doua metode (considerate pana in prezent ca
fiind independente) de a construi tensori Stackel-Killing, din tensori
Killing- Yano sau din vectori Killing conformi (algoritmul Koutras), poate
fi gasita o legatura prin dualitate Hodge. Se va arata ca tensorii
Killing-Yano formeaza o algebra Lie sub actiunea parantezei
Schouten-Nijenhuis. De asemenea, folosind dualitatea geometrica, vor fi
construite si discutate metricile duale pentru spatiu-timpul Kimura IIC.
La nivel cuantic, folosind tensorii Killing-Yano de rang trei, vor fi
construiti si studiati operatorii de tip Dirac, si se va arata ca
existenta acestor tensori conduce la o teorie lipsita de anomalii.
- Dr. Andrei Micu, IFIN-HH
"Solutii supersimetrice si nesupersimetrice in modele din teoria
corzilor heterotice in prezenta campurilor de materie"
faza finala pe
anul acesta de la contractul CNCSIS 3/3.11.2008
- Acad. Horia Scutaru, IFIN-HH
"Descrierea dualitatii dintre liftinguri covariante si canale
cuantice covariante"
faza de Proiect IDEI 497/2009.
- 08.12.2009/12:00
Dr. Sabin Stoica, DFT-IFIN
"Calculul analitic al partilor de structura nucleara a ratelor de emisie
ale axionilor din stele neutronice prin procese de bremsstrahlung",
Proiect ID-975, director de proiect Sabin Stoica, (Abstract)
Vor fi prezentate calculul ratelor de emisie a axionilor din stele
neutronice prin procese de bremsstrahlung nucleon-nucleon. In calcule va
fi inclusa contributia nucleara la acest proces data de un potential de
tip OPE. Vor fi calculate ratele de emisie in cazurile nn, pp si np,
precum si in regimurile nedegenerat si degenerat.
- Bogdan Popovici, DFT-IFIN
"Elaborarea metodei SLV si analiza canalului Bs0-->pi + Ds- cu ajutorul
acestei metode",
proiect ID-959, director de proiect Sorina Popescu, (Abstract)
Se va prezenta elaborarea metodei Sliding Vertex de reconstructie a
particulelor neutre din conditii cinematice, se vor investiga conditiile
necesare pentru succesul aplicarii metodei si se vor justifica
aproximatiile. Se va afce o analiza a aplicarii acestei metode la un canal
concret de dezintegrare a particulelor ce contin cuarcul b.
- Dr. Victor Barsan, DFT-IFIN
"Studiul solidului anarmonic clasic bi-dimensional",
Proiect IDEI 2008 nr. 953; director de proiect: Victor Barsan, (Abstract)
Folosind metoda matricii de transfer si rezultate analitice
obtinute recent pentru un oscilator cuartic in camp electric, se
calculeaza temperatura critica a unui agregat planar de lanturi cuplate,
in functie de constanta de cuplaj dintre lanturi. Se calculeaza analitic
susceptibilitatea electrica in vecinatatea punctului critic si indicii
critici ai sistemului.
- 03.12.2009/12:00
Dr. Nicolae Grama, DFT IFIN-HH
"A new uniform asymptotic approximation of the 3d scattering wave function
for a central potential"
(Abstract)
A uniform asymptotic approximation of the 3D scattering wave function for
a central potential is obtained by using a new Ansatz on the form of the
solution. This Ansatz employs the regular reduced radial wave function of
zero orbital angular momentum, generated by the problem itself, rather
than a standard special function. The uniform asymptotic approximation of
the 3D scattering wave function allows finding the scattering amplitude
without using the partial wave expansion.
The method is applied to the scattering by a pure Coulomb potential. In
contrast to the uniform asymptotic approximation of the 3D Coulomb wave
function based on the Airy function that breaks down at the caustic
$\xi=0$, the uniform asymptotic approximation obtained in the present
paper is valid over the whole range of the variables.
It is shown that the uniform asymptotic approximation of the 3D Coulomb
scattering wave function obtained through the new Ansatz is in fact the
exact Gordon solution.
- 26.11.2009/12:00
Dr. Lucian Miu, Institutul National de Cercetare Dezvoltare in Fizica Materialelor.
"Dinamica vortexurilor in supraconductorii cu temperatura critica ridicata"
- 19.11.2009/12:00
Dr. Ciprian Acatrinei, DFT-IFIN
"Cauzalitate in teorii de camp definite pe spatii necomutative"
(Abstract)
Teoriile de camp definite pe spatii necomutative
sunt nelocale si pun probleme la definirea notiunii de cauzalitate.
Folosind o abordare care pune accentul pe bilocalitatea excitatiilor
fundamentale pe spatii necomutative, vom vedea in ce masura se poate vorbi
de cauzalitate si de relatii de dispersie in aceste teorii.
- 12.11.2009/12:00
dl Petrica Buganu, doctorand
"Un model solubil ce are ca simetrie limita X(5) si care elimina unele
neajunsuri ale tratarilor anterioare" (Abstract)
Sunt propusi Hamiltonieni solubili pentru coordonatele de deformare
intrinseci \beta si \gamma. Functiile proprii ale Hamiltonianului in
\gamma sunt functii periodice sferoidale, in timp ce Hamiltonianul in
\beta, pentru care este folosit un potential Davidson, admite functii
proprii exprimate in functie de polinoamele Laguerre generalizate. Modelul
propus se reduce la X(5) in limita lui |\gamma|-mic. Unele neajunsuri ale
modelului X(5), cum ar fi periodicitatea functiilor si hermiticitatea
Hamiltonianului in \gamma, sunt absente in modelul prezent. Rezultatele
aplicatiilor numerice pentru $^{150}$Nd, $^{154}$Gd si $^{192}$Os sunt in
buna concordanta cu datele experimentale. Comparatiile cu datele X(5)
sugereaza ca modelul prezent ofera o descriere cantitativa mai buna a
datelor experimentale, in special pentru energiile de excitatie din banda
gamma.
- Dr. Sabin Stoica, IFIN-HH
"Dezintegrarea beta dubla; calculul elementelor de matrice nucleare pentru
izotopul Ca48."
Faze proiect PN09370106
- 05.11.2009/12:00
dl Radu Budaca, doctorand
"Excitatii colective dipolare in clusterii de sodiu.
" (Abstract)
Cateva proprietati ale clusterilor de sodiu mici si medii sunt
descrise cu ajutorul aproximatiei fazelor itamplatoare (RPA), folosind
o baza uniparticula sferica proiectata. Puterile de oscilator
calculate cu un operator de tranzitie dipolara de tip Schiff si
foldate cu functii lorentziene sunt folosite pentru calculul
spectrului sectiunii aficace de fotoabsorbtie. Rezultatele obtinute
sunt folosite in continuare pentru stabilirea dependentei frecventei
plasmonice de numarul de constituenti ai clusterului.
Polarizabilitatile electrice statice ale clusterilor, excitate in
stari RPA dipolare, sunt deasemenea calculate. Compararea rezultatelor
obtinute cu datele experimentale corespunzatoare prezinta in general
un acord foarte bun.
Regula de suma cu pondere liniara in energie pentru operator de
tranzitie dipolara de tip Schiff difera de regula de suma
Thomas-Reiche-Kuhn (TRK) prin cativa termeni de corectie ce depind de
numarul componentelor din sistem. In concluzie, rezultatele RPA pentru
clusterii de Na satisfac o regula de suma TRK modificata.
- 29.10.2009/12:00
dl Radu Budaca, doctorand
"Descrierea semiclasica a rotatorului rigid triaxial
"
[slides-pdf]
(Abstract)
Un Hamiltonian de rotator este tratat cu ajutorul unui principiu
variational dependent de timp, folosind ca functie de proba o stare
coerenta. Punctele critice ale suprafetei de energie constanta depind
de relatiile de ordonare intre momentele de inertie. Pentru toate
aceste cazuri este derivata o frecventa de wobbling specifica.
Tranzitia dintre doua faze este discutata in legatura cu un Hamiltonian
constrans. Sunt indicate patru perechi distincte de coordonate canonice
complexe. Fiecare dintre acestea, conduc, dupa cuantificare, la o
reprezentare bozonica diferita a componentelor momentului cinetic.
Separarea energiei potentiale este tratata in una din cele patru baze
din spatiul fazelor. Una din descrierile semiclasice este folosita
pentru explicarea spectrului Yrast al nucleului de Er(158), pentru care
se obtine o concordanta excelenta cu datele experimentale.
- Prezentarea proiectului de investitii CP 145/2007, Raport etapa 3,
Prezinta: director proiect Dr. Sabin Stoica, DFT-IFIN
- 22.10.2009/12:00
Dr. F. Carstoiu si Dr. S. Misicu, DFT-IFIN
"Equation of state (EOS) and Bose-Einstein condensation (BEC) in cold alpha matter.
"
[slides-pdf]
(Abstract)
We analyze an ideal (neutral) alpha matter at T=0 using methods borrowed from Bose liquid theory, adapted for strong interactions.Two body
correlation functions are obtained from Pandharipande-Bethe equation.
Convergence of the cluster expansion of the energy is carefully analyzed
by including cluster diagrams up to 4th order. The high density regime is
studied within HNC/0 and HNC/4 approximations. Finally we show that high
order terms in the expansion of BE condensation fraction lead to a
significant depletion at densities around the saturation value.
- 15.10.2009/12:00
Dr. Andrei Micu, IFIN-HH
"Compactificari ale teoriei corzilor heterotice pe varietati cu
structura SU(2)" (Abstract)
Faza PN 09 37 0102/2009
Comapctificari ale corzilor heterotice in patru dimensiuni reprezinta un punct de interes in fenomenologia teoriei corzilor. Se vor prezenta compactificari ale corzlilor heterotice pe varietati K3 x T^2 si generalizari ale acestora de tipul varietatilor sase-dimensionale cu structura SU(2).
- 08.10.2009/12:00
Dr. Margarit Rizea, IFIN-HH
"Solution of the two-dimensional time-dependent
Schrodinger equation applied to nuclear proton decay" (Abstract)
A rigorous approach to study the temporal evolution of
physical processes is to follow the development in time of a given initial
state, by numerically solving the time-dependent Schrodinger equation.
This represents a natural modeling of the dynamical behaviour.
We considered the equation in two spatial coordinates, to describe deformed
nuclear shapes. The Hamiltonian is discretized by special, functionally
fitted difference formulae of the derivatives and then a Crank-Nicolson
scheme is applied. The resulting linear system with large sparse matrix is
solved by a variant of Conjugate Gradient Method. The numerical solution
has been used to the description of the proton decay. We also discuss the
treatment of numerical boundary conditions, the preparation of the initial
wavefunction and the calculation of the decay rate through the flux.
- 01.10.2009/12:00
Dr. Sergiu Cojocaru, IFIN-HH
"Ecuatia Schrodinger pe retele finite si transformarea Fourier
discreta" (Abstract)
Transformarea Fourier este o metoda standard de studiere a problemei
interactiilor pe retele periodice, in special in materia condensata, cand
este vorba de stari cuantice pe retele infinite. Voi arata ca tratarea
acestei metode in cazul retelor finite scoate in evidenta anumite stari
cuantice absente in solutiile cunoscute. Luand ca exemplu modelul
Heisenberg de spini, voi discuta relatia acestei metode cu solutia exacta
Bethe Ansatz pentru lant periodic si cu conditii de granita arbitrare; voi
prezenta si unele rezultate exacte ce tin de retele bidimensionale finite.
- 24.09.2009/12:00
Dr. Irinel Caprini, IFIN-HH
"Determination of the QCD strong coupling from hadronic decays of
the tau lepton" (Abstract)
The hadronic decays of the tau lepton represent one of the best methods
for the determination of the strong coupling $\alpha_s$, the fundamental
parameter of QCD. I will present a determination based on a new
perturbation expansion, which reproduces the low coefficients known from
Feynman digrams and describes correctly the high-order behaviour of the
series. The results clarify the origin of a discrepancy between two
methods applied recently in the literature, and lead to a precise
determination of $\alpha_s$.
- 17.09.2009/12:00
Mirela Babalic, IFIN-HH si Universitatea Craiova
"Corelarea formularilor k-simetrica si pur spinoriala pentru
superparticula si supermembrana in D=11" (Abstract)
Studiem relatia intre formularea kappa-simetrica si respectiv pur spinoriala a superparticulei si supermembranei in unsprezece dimensiuni folosind metoda dezvoltata recent de Berkovits pentru superstring (in D=10). In lucrare de fata incercam sa extindem aceasta metoda la supermembrana, folosind analiza superparticulei in D=11 ca pe un exercitiu. Aratam ca este posibil sa utilizam constrangerile de reparametrizare si in formularea pur spinoriala a supermembranei prin introducerea unui sector neminimal si efectuarea unei transformari de similitudine. Sarcina BRST rezultata este de tip conventional si se observa a avea legatura cu sarcina BRST a supermembranei k-simetrice intr-o formulare in care toate constrangerile de clasa II sunt "de-fixate" gauge la constrangeri de clasa I. In analiza noastra descoperim un candidat natural pentru un analog (necovariant) al b-ghostului in cazul supermembranei.
(Articolul a fost publicat in JHEP si apare si pe arXiv:hep-th/0105050v2)
- Acad. Horia Scutaru, IFIN-HH
"Determinarea structurii generale a canalelor cuantice covariante"
Faza de contract IDEI 497/2009, cod CNCSIS ID-1389.
- 10.09.2009/12:00
Dr. Ciprian Acatrinei, IFIN-HH
"Bilocalitate si cauzalitate pe spatii necomutative" (Abstract)
Faza IDEI 464/2009
Se vor prezenta modificarile introduse de necomutativitatea spatiului
pentru teorii de camp scalare. In particular, excitatiile fundamentale
capata caracter bilocal, in contradistinctie cu natura punctuala a
excitatiilor teoriilor uzuale. In asemenea teorii, se pune imediat
problema definirii/mentinerii cauzalitatii si unitaritatii.
Vom discuta in detaliu prima chestiune, precum si posibilitatea
formularii relatiilor de dispersie pentru diverse tipuri de procese.
- Dr. Mihai Visinescu, IFIN-HH
"Simetrii ascunse pe spatii de interes in gravitatie si cosmologie"
(Abstract)
Faza IDEI 571/2009
SConformal Killing-Yano tensors on higher dimensional spacetimes generate
hidden symmetries intimately related to the integrability of the geodesic
motions and separability of Hamilton-Jacobi, Klein-Gordon, Dirac equations
in these backgrounds. The existence of conformal Killing-Yano tensors on
spacetimes endowed with a mixed 3-Sasakian structure is proved. Some
explicit examples of Einstein spacetimes with mixed 3-Sasakian structures
are constructed. These spacetimes admit three orthogonal Killing vector
fields, one timelike and the others spacelike. The distribution spanned by
them is integrable, defines a 3-dimensional Riemannian foliation having
totally geodesic leaves of constant curvature.
- Dl.Bogdan Pastrav , IFIN-HH
"Studiul proceselor de emisie a neutrinilor si axionilor in stele neutronice"
(Abstract)
Faza Contract Idei 444/2009, ID_975
Investigarea emisiei de neutrini si axioni prin procese de
bremsstrahlung din stele neutronice; includerea efectelor nucleare in
procesele de emisie printr-un potential nuclear de tip OPE.
- Dr. Sabin Stoica, IFIN-HH
"Metode cinematice pentru optimizarea studiului dezintegrarilor mezonilor B"
(Abstract)
Faza Contract IDEI 541/2009, ID_959
Intelegerea limitelor metodelor cinematice folosite in
literatura cinematice; metodea Sliding Vertex de reconstructie a
particulelor neutre din conditii cinematice.
- 03.09.2009/12:00
Dr. Dan Grigore, IFIN-HH
"Renormarea gravitatiei cuantice in aproximatia liniara" (program PN II)
- 20.08.2009/12:00
Dr. Victor Barsan, IFIN-HH
"Studiul modelului de solid anarmonic clasic intr-o dimensiune" (Faza IDEI 953/2008)
- 30.07.2009/12:00
Dr. Adrian Tanasa, IFIN-HH
Teorii cuantice de camp si spatiul Minkowski (Abstract)
Singurele modele renormabile de teorii de camp pe un spatiu
necomutativ sunt euclidiene. Propunem aici un model minkowskian care este
un candidat viabil pentru a fi si renormabil. Pentru a demonstra
aceasta renormabilitate,
propunem o adaptare la acest cadru necomutativ a metodei
ecuatiilor de flux ale lui Polchinski. In acest scop prezentam initial
demonstratia renormabilitatii modelului euclidian asociat. In cele din
urma vom prezenta cum aceasta demonstratie s-ar putea extinde la modelul
minkowskian.
- 23.07.2009/12:00
Dr. Petre Dita, IFIN-HH
KM Matrix Moduli, Decay Constants and Form Factors Determination from Data
- 16.07.2009/12:00
Dr. Ovidiu Patu, ISS
Correlation Functions of One-Dimensional Anyons [slides-pdf] (Abstract)
We consider a system of one-dimensional hard-core anyons interacting
via a δ-function potential, which simulates the hard-core repulsion,
and are free otherwise. The large time and distance asymptotic behavior
of the field-field correlation functions computed rigorously with the
help of an associated Riemann-Hilbert problem is presented. The obtained
asymptotic behavior of the correlators differs from the predictions of
conformal field theory (Luttinger liquid).
- 9.07.2009/12:00
Dr. St. Berceanu, IFIN-HH
The Jacobi group and the squeezed states - some comments (Abstract)
Firstly we recall the main properties of the Jacobi group
GJ1 and its relationship with the squeezed states
of quantum optics. Imposing hermitian conjugacy to the generators of the
Jacobi algebra, we find out the form of the weight function appearing in
the scalar product. From the explicit form of the reproducing kernel, we
find out the expression multiplier in the representation of the Jacobi
group GJ1.
- 2.07.2009/12:00
Prof. Dr. Dorin Poenaru, IFIN-HH
Modele uni-particula de oscilator sferoidal si semi-sferoidal armonic
Faza IDEI (Contract 123/01.10.2007)
- 25.06.2009/12:00
Dr. Gabriela Buica, ISS
Multiphoton ionization of Ca by linearly and circularly polarized laser pulses
- 18.06.2009/12:00
Dr. Iulia Ghiu, Univ. of Bucharest, Faculty of Physics
Local transformations of entangled states (Abstract)
Suppose that we have two entangled states that cannot be converted to any of other two states by local operations and classical communication. We analyze the possibility of locally transforming a superposition of the first two states into a superposition of the other two states. By using the Nielsen's theorem we find the necessary and sufficient conditions for this conversion to be performed.
References:
[1] Iulia Ghiu, M. Bourennane, and A. Karlsson,
'Entanglement-assisted local transformations between inequivalent classes of three-particle entangled states', Physics Letters A 287, 12-18 (2001).
[2] Iulia Ghiu, 'Local transformations of superpositions of entangled states', Physics Letters A 373, 922-926 (2009).
- 11.06.2009/12:00
Dr. Doru Delion, IFIN-"HH"
Structura fina in dezintegrarea α a nucleelor grele si supragrele
- 4.06.2009/12:00
Dr. Nicolae Sandulescu, IFIN-"HH"
Pairing Correlations in Nuclei: BCS-based models versus exact solutions (Abstract)
For about 50 years BCS-based models are commonly used
to treat pairing in atomic nuclei. However, their basic
features and their limit of validity when applied to
finite Fermi systems such as atomic nuclei or metallic
grains are still debated issues. In the first part of the
seminar I shall discuss the magnitude of coherence length
in nuclei as predicted by Bogoliubov de Gennes approach.
Contrary to the common beleaves, it will be shown that in
nuclei the coherence length could become smaller than the
nuclear radius. Then, using exactly solvable Richardson-Gaudin
models, I shall discuss the accuracy of BCS-based approximations
for treating like-particle pairing (neutron-neutron or proton-proton)
and neutron-proton pairing.
Note: to facilitate the discussions not only with experts in
nuclear physics, all these issues will be addressed keeping as
much as possible a general/elementary level.
- 28.05.2009/12:00
Dr. Mihai Mirea, IFIN-"HH"
Efect Landau-Zener generalizat si efectul dinamic de spargere de perechi
- 21.05.2009/12:00
Dr. Cristian M. Teodorescu, INCDFM
Studii actuale in domeniul oxizilor semiconductori magnetici diluati [slides-pdf] (Abstract)
Domeniul semiconductorilor diluati magnetici este de mare actualitate de
cca. 20 de ani. In acest domeniu, problematica semiconductorilor oxidici
diluati cu metale de tranzitie a captat interesul comunitatii
stiintifice in ultimii 6-7 ani. Se va efectua un scurt review al
situatiei actuale, cu accent asupra reproductibilitatii relativ reduse a
rezultatelor, in special in ceea ce priveste proprietatile magnetice. Se
schiteaza o explicatie a acestei reproductibilitati reduse, ocazie cu
care se introduc si fundamentele teoriei interactiei de schimb
indirecte, mijlocita de purtatorii de sarcina din semiconductori (RKKY).
Se prezinta rezultate recent obtinute, pe urmatoarele sisteme: (i) oxid
de zinc dopat cu cobalt, sintetizat prin PLD, prin tehnica sol-gel si
prin metode electrochimice; (ii) oxid de titan dopat cu fier, sintetizat
prin PLD; (iii) oxid de vanadiu dopat cu cobalt, sintetizat prin PLD. Se
prezinta incercarea de corelare a proprietatilor magnetice, obtinute
prin VSM si MOKE, cu structura atomica locala, obtinuta prin EXAFS si cu
compozitia chimica si starile de ionizare, obtinute prin XPS si XANES.
Se prezinta si informatii structurale: difractie de raze X, precum si
investigatii morfologice: SEM, AFM. In ultima parte a seminarului se vor
evidentia fenomenele de suprafata si interfata si se vor prezenta
rezultate preliminare obtinute prin aplicarea teoriei RKKY pe sisteme
bidimensionale.
Abrevieri folosite:
RKKY = Ruderman-Kitell-Kasuya-Yosida
PLD = pulsed laser deposition
VSM = vibrating sample magnetometry
MOKE = magneto-optical Kerr effect
EXAFS = extended X-ray absorption fine structure
XANES = X-ray absorption near-edge structure
SEM = scanning electron microscopy
AFM = atomic force microscopy
- 14.05.2009/12:00
Dr. Iulia Ghiu, University of Bucharest, Faculty of Physics
Local transformations of superpositions of entangled states
Anulat din cauza lucrarilor la sala de seminar.
Va rog sa scuzati neplacerile provocate.
Se va reprograma (nu pierdem nimic ;-))
- 7.05.2009/12:00
Dr. Cristian M. Teodorescu, INCDFM
Studii actuale in domeniul oxizilor semiconductori magnetici diluati
Anulat din cauza lucrarilor la sala de seminar.
Va rog sa scuzati neplacerile provocate.
Reprogramat pe data de 21.05.2009 (vedeti mai sus).
- 30.04.2009/12:00
Dr. Madalina Boca, University of Bucharest, Faculty of Physics
Non-linear Compton effect with a laser pulse [slides-pdf] (Abstract)
Work done in collaboration with Viorica Florescu:
We theoretically investigate the scattering of intense laser radiation on energetic electrons. The laser field is described as a pulse with a fixed propagation direction. The transition amplitude in the monochromatic limit contains a four-dimensional δ function, expressing the momentum and energy conservation, and leading to a discrete spectrum of the emitted radiation. By, contrast, in the case of a pulse one obtains the product of a three-dimensional δ function with an one-dimensional integral evaluated numerically. We study the dependence of the emitted photon spectrum on the pulse duration. In contrast with the monochromatic case, where the spectrum is discrete, in our case one obtains a continuous distribution with a succession of maxima located near the corresponding discrete values.
References
- Eberly J 1969 Prog. in Optics 7 359.
- Bula C 1996 Phys. Rev. Lett 76, 3116.
- Panek P, Kaminski J Z, and Ehlotzky F 2002 Opt. Commun 213 121.
- Chouffani K et al 2006 Laser and Particle Beams 24 411.
- 23.04.2009/12:00
Andrei Neacsu, IFIN-"HH"
Neutrinoless double beta decay of 48Ca [slides-pdf]
- 15.04.2009/12:00
Dr. Dan Grecu, IFIN-"HH"
Moduri liniare si neliniare intr-o plasma cu praf. Influenta variatiei sarcinei electrice pe particalele de praf.
[slides-pdf]
Faza 1, Proiect Nucleu 2009
- 9.04.2009/12:00
Dr. Alexandru Nemnes, University of Bucharest, Faculty of Physics
Tranzistori nanometrici in formalismul matricii R [slides-pdf]
(Abstract)
Transportul balistic in tranzistori cu efect de camp este analizat in formalismul matricii R. Acesta a fost dezvoltat in contextul problemelor de imprastiere din cadrul fizicii nucleare, iar in prezent reprezinta un instrument valoros pentrul studiul transportului rezonant in sisteme mezoscopice. Se vor caracteriza pe scurt curbele I-V pentru diferite structuri (planare, cilindrice). In incheiere, se vor discuta perspectivele introducerii functiilor Gamow in analiza proceselor de imprastiere inelastice.
Outline:
- Introducere in formalismul Landauer-Buettiker
- Formalismul matricii R
- Aplicatie: transistor cu efect de camp la scara nanometrica
- De discutat: aplicatii ale functiilor Gamow in procese de imprastiere inelastice
- 2.04.2009/12:00
Dr. Stefan Carstea, IFIN-"HH"
Effects of singularities in a nonlinear discrete world [slides-pdf]
- 26.03.2009/12:00
Dr. Dragos-Victor Anghel, IFIN-"HH"
A Fresh Look at Fractional Exclusion Statistics.
A critical review of FES and corrections
[slides-pdf]
(Abstract)
The concept of fractional exclusion statistics is critically
revised. I show that it leads to inconsistencies in the calculation of the
particle distribution that maximizes the partition function. These
inconsistencies appear when mutual exclusion statistics is manifested
between different subspecies of particles in the system. In order to
eliminate these inconsistencies, I introduce new mutual exclusion
statistics parameters, which are proportional to the dimension of the
Hilbert sub-spaces on which they act. These new definitions lead to
properly defined particle distributions and thermodynamic properties.
The fractional exclusion statistics is manifested in general in systems of
interacting particles and the calculated exclusion statistics parameters
have indeed the properties conjectured here.
References
- D. V. Anghel, Properties of fractional exclusion statistics in interacting particle systems, accepted in Rom. J. Phys.; arXiv:0804.1474.
- D. V. Anghel, Fractional exclusion statistics in general systems with interaction, Phys. Lett. A 372, 5745 (2008); arXiv:0710.0728.
- D. V. Anghel, The thermodynamic limit for fractional exclusion statistics, J. Phys. A: Math. Theor. 40 F1013-F1019 (2007); arXiv:0710.0724.
- 19.03.2009/12:00
Dr. Irinel Caprini, IFIN-"HH"
CKM matrix elements from semileptonic B decays
[slides-pdf]
- 12.03.2009/12:00
Dr. Petre Dita, IFIN-"HH"
Paralipomena around Sylvester matrices
[slides-pdf]
- 5.03.2009/12:00
Dr. Andrei Micu, IFIN-"HH"
Stabilizarea modulilor in compactificari ale teoriei corzilor heterotice [slides-pdf]
- 12.02.2009/13:00
Drd. Alexandru Grecu, IFIN-"HH"
Comparative Study of Symmetry Effects on Modulational Instability of Nonlinear Schroedinger Equations - Deterministic Approach
- 8.01.2009/12:00
Dr. Adrian Tanasa, IFIN-"HH"
Polinoame topologice de grafuri si teorii cuantice de camp [slides-pdf]
(Abstract)
Se prezinta fluxul grupului de renormare al unui model scalar necomutativ. Acest calcul este simplificat considerabil datorita descompunerii propagatorului necomutativ intr-o suma de doi termeni: propagatorul "obisnuit" comutativ si o corectie necomutativa. Aceasta descompunere permite printre altele implementarea reprezentarii parametrice a amplitudinilor Feynman, reprezentare ce generalizeaza rezultatele teoriilor comutative.