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In this third episode of the second season Nic and Rebeca chat about equality in science before inviting Nikolai Piskunov to the microphone. Nikolai is a professor at the Department of Physics and Astronomy at Uppsala University. He was visiting Lund Observatory to give a talk about high-resolution transit spectroscopy and graciously agreed to make an appearance on the podcast.This season we are a
In this third episode of the podcast Nic and Rebecca invite Jens Hoeijmakers to the mic and chat to him about ultra-hot Jupiters and their atmospheres. Thereafter they take a closer look at a comet, which is named after the its two discoverers: Michel Giacobini and Ernst Zinner.
We study a random surface representation of Wilson loops in Z(2) gauge theory. The weights consist of an area factor, which dominates at strong coupling, and an excluded volume factor flavouring crumpled surfaces. We examine the latter one in some detail in three as well as four dimensions by use of Monte Carlo methods. In three dimensions, the critical behaviour of the surfaces is found to be det
We present high statistics MC calculations of the static potential in three-dimensional SU(2) for a wide range of β values on a 243 lattice. The deviations from area law are unambiguously demonstrated by use of 2nd lattice R derivative. After a clear crossover at β=4.5 the data show signs of an effective string roughening up to β=6.5, while scaling is not strictly obeyed in this interval. Pure fer
Convincing evidence of a nonvanishing string tension in the continuum limit of compact three-dimensional U(1) gauge theory is presented. It is based on Monte Carlo measurements of Wilson loops on a 323 lattice at =2.0 and 2.2. The observed string tensions at these couplings are consistent with the Polyakov theory. Also, a very clean signal of a string vibrational contribution to the potential is o
The deconfinement temperature Tc of (2+1)-dimensional SU(2) gauge theory is measured on lattice sizes varying from 2 × 202 to 6 × 602 and with β in the rate 3-9. Approximative scaling is found for β > 6.5 and Tc/√σ = 0.94 ± 0.03 is obtained. This value is in excellent agreement with (3/π) 1 2, as predicted from the breakdown of SU(2) confinement in terms of an effective scalar string theory.
Numerical evidence for a nonvanishing 0++ glueball mass in three-dimensional SU(2) is presented. By using a long-distance correlation Monte Carlo method we obtain m0++ = (4.7±1.2)√σ in the β-range 4.0-6.5. The measurements are consistent with 1/β-scaling. The relevance of this result for SU(2) in four dimensions at finite temperature is briefly discussed.
A package written in C for identifying variable dependencies in tables of data is presented. The key ingredient is the δ-test, which establishes dependency structures by exploiting the properties of continuous functions using conditional probabilities formed out of the data. The method estimates most relevant variables, embedding dimensions and noise levels. The program, which is self-contained, a
A brief review is given for the use of feed-back artificial neural networks (ANN) to obtain good approximate solutions to combinatorial optimization problems. The key element is the mean field approximation (MFT), which differs from conventional methods and "feels" its ways towards good solutions rather than fully or partly exploring different possible solutions. The methodology, which is illustra
A feed-forward neural network method is developed for reconstructing the invariant mass of hadronic jets appearing in a calorimeter. The approach is illustrated in W→qq, where W-bosons are produced in pp reactions at SPS collider energies. The neural network method yields results that are superior to conventional methods. This neural network application differs from the classification ones in the
We explore the possibilities of using the complex Langevin equation to Monte Carlo generate configurations of gauge theories with static charges present in the action. Successful results are obtained for systems that possess nontrivial saddle-point (classical) solutions. For that reason the algorithm works impressively for two-dimensional U(1) in the entire β-range whereas for three- and four-dime
By using the Langevin equation with complex action it is possible to generate (complex) configurations in the charged sector of gauge theories. We test the algorithm in the case of two-dimensional U(1) gauge theory and are able to measure the string tension with great precision and modest use of computer time for a separation of the charged particles where a conventional Wilson loop would have a v
We have measured the lattice size dependence of the lightest glueball mass in SU(2) and SU(3) gauge theory at =2.2 and 2.3 [SU(2)] and =6.0 [SU(3)]. We observe an increase in the glueball mass when the lattice size shrinks below a critical value. The magnitude of this length scale, which we interpret as the physical size of the glueball, is roughly the same for SU(2) and SU(3) when expressed in un
The static potentials from bosonic string models are examined to the two-loop level. Available MC data for 4-dimensional SU(3) are in approximate agreement with the universal leading order predictions but fail to reproduce the Nambu string when the two-loop terms are included in the analysis. We also confront Nambu string model predictions for Tc σ with SU(2), SU(3) and SU(N → ∞) MC data. In the S
By Monte Carlo calculations on a 124 lattice we investigate four-dimensional SU(2) lattice gauge theory with respect to the conjecture that at large distances this theory reduces approximately to two-dimensional SU(2) lattice gauge theory. We find good numerical evidence for this conjecture. As a by-product we also measure the SU(2) string tension and find reasonable agreement with scaling. The "a
We study 3-dimensional SU(2) lattice gauge theory with respect to dimensional reduction. By Monte Carlo calculations we find that this reduction is valid to a good approximation (within ≈10%). The adjoint string tension is found to scale approximately. We also compare the adjoint string tension with a string theory.
Cross sections for glueball production in hadron-induced reactions are estimated using the gluon-gluon fusion mechanism. For pp → θ(1700, JPC = 2++)X one finds σθ ∼ 2-10 mb in ISR-collider energy range. This cross section should give a clean experimental signal given the substantial KK decay mode observed in ψ → γθ.
SU(2) lattice gauge theory in three dimensions is investigated on a 162×32 lattice. We find that R>×T Wilson loops are well described by a simple string theory for β in the (approximate) scaling region.
Recent SU(3) lattice Monte Carlo data (244 and 164) are analyzed in terms of a simple string model. Good agreement is found. Observed similarities between SU(3) and three-dimensional SU(2) indicate that the string theory is indeed an effective one.
Existing bag-model calculations for the masses of lowest-lying glueball states are extended and reviewed and compared to the present lattice Monte Carlo calculations. The predicted spectra agree remarkably well.
