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In this letter we present some stringy corrections to black hole spacetimes emerging from string T-duality. As a first step, we derive the static Newtonian potential by exploiting the relation between the T-duality and the path integral duality. We show that the intrinsic non-perturbative nature of stringy corrections introduces an ultraviolet cutoff known as zero-point length in the path integral duality literature. As a result, the static potential is found to be regular. We use this result to derive a consistent black hole metric for the spherically symmetric, electrically neutral case. It turns out that the new spacetime is regular and is formally equivalent to the Bardeen metric, apart from a different ultraviolet regulator. On the thermodynamics side, the Hawking temperature admits a maximum before a cooling down phase towards a thermodynamically stable end of the black hole evaporation process. The findings support the idea of universality of quantum black holes.
The effect of a non-zero strangeness chemical potential on the strong interaction phase diagram has been studied within the framework of the SU(3) quark-hadron chiral parity-doublet model. Both, the nuclear liquid-gas and the chiral/deconfinement phase transitions are modified. The first-order line in the chiral phase transition is observed to vanish completely, with the entire phase boundary becoming a crossover. These changes in the nature of the phase transitions are expected to modify various susceptibilities, the effects of which might be detectable in particle-number distributions resulting from moderate-temperature and high-density heavy-ion collision experiments.
A unified chiral mean field approach is presented for QCD thermodynamics in a wide range of temperatures and densities. The model simultaneously gives a satisfactory description of lattice QCD thermodynamics and fulfills nuclear matter and astrophysical constraints. The resulting equation of state can be incorporated in relativistic fluid-dynamical simulations of heavy-ion collisions and neutron stars mergers. Access to different regions of the QCD phase diagram can be obtained in simulations of heavy-ion data and observations of neutron star mergers.
Study of the photon strength functions and level density in the gamma decay of the n + 234U reaction
(2019)
The accurate calculations of neutron-induced reaction cross sections are relevant for many nuclear applications. The photon strength functions and nuclear level densities are essential inputs for such calculations. These quantities for 235U are studied using the measurement of the gamma de-excitation cascades in radiative capture on 234U with the Total Absorption Calorimeter at n_TOF at CERN. This segmented 4π gamma calorimeter is designed to detect gamma rays emitted from the nucleus with high efficiency. This experiment provides information on gamma multiplicity and gamma spectra that can be compared with numerical simulations. The code DICEBOXC is used to simulate the gamma cascades while GEANT4 is used for the simulation of the interaction of these gammas with the TAC materials. Available models and their parameters are being tested using the present data. Some preliminary results of this ongoing study are presented and discussed.
Early, non-invasive sensing of sustained hyperglycemia in mice using millimeter-wave spectroscopy
(2019)
Diabetes is a very complex condition affecting millions of people around the world. Its occurrence, always accompanied by sustained hyperglycemia, leads to many medical complications that can be greatly mitigated when the disease is treated in its earliest stage. In this paper, a novel sensing approach for the early non-invasive detection and monitoring of sustained hyperglycemia is presented. The sensing principle is based on millimeter-wave transmission spectroscopy through the skin and subsequent statistical analysis of the amplitude data. A classifier based on functional principal components for sustained hyperglycemia prediction was validated on a sample of twelve mice, correctly classifying the condition in diabetic mice. Using the same classifier, sixteen mice with drug-induced diabetes were studied for two weeks. The proposed sensing approach was capable of assessing the glycemic states at different stages of induced diabetes, providing a clear transition from normoglycemia to hyperglycemia typically associated with diabetes. This is believed to be the first presentation of such evolution studies using non-invasive sensing. The results obtained indicate that gradual glycemic changes associated with diabetes can be accurately detected by non-invasively sensing the metabolism using a millimeter-wave spectral sensor, with an observed temporal resolution of around four days. This unprecedented detection speed and its non-invasive character could open new opportunities for the continuous control and monitoring of diabetics and the evaluation of response to treatments (including new therapies), enabling a much more appropriate control of the condition.
Die vorliegende Dissertation untersucht die Nichtgleichgewichtsdynamik von relativistischen Schwerionenkollisionen ausgehend von der anfänglichen Produktion von Teilchen durch den Zerfall von Strings, der Bildung eines Quark-Gluon-Plasmas (QGP), dessen kinetische und chemische Äquilibrierung als Funktion der Zeit sowie seine Transporteigenschaften im Gleichgewicht bei endlicher Temperatur und endlichem chemischen Potential. Ein Verständnis der frühen Phase der Schwerionenkollisionen ist insbesondere von großen Interesse, da letztere eine Verbindung zwischen den ersten Nukleon-Nukleon Kollisionen und der Quark-Gluon-Plasma Phase herstellen, die zu einem späteren Zeitpunkt ein gewisses Maß an Thermalisierung zeigt. Allerdings können nur Nichtgleichgewichts-Theorien eine Verbindung zwischen dem anfänglichen QGP und seiner - zumindest partiellen - Thermalisierung herstellen. Um die Dynamik eines stark wechselwirkenden Mediums wie des Quark-Gluon-Plasmas zu beschreiben, reichen übliche Transportgleichungen (basierend auf der Boltzmann-Gleichung) nicht aus und es müssen komplexere Theorien, die auch für stark korrelierte Medien geeignet sind, angewendet werden. Hier kommen hydrodynamische Simulationen oder Transportrechnungen - basierend auf verallgemeinerten Transportgleichungen - zum Einsatz. Solche verallgemeinerte Transportgleichungen, wie die Kadanoff-Baym-Gleichungen, ergeben sich aus der quantenmechanischen Nichtgleichgewichts-Vielteilchentheorie, in der Green’s- Funktionen in Minkowski Raum-Zeit die interessierenden Größen sind, um die Dynamik des betrachteten Mediums zu beschreiben. Mit geeigneten Näherungen kann man so kinetische Transportgleichungen erhalten, die eine einheitliche Behandlung von stabilen und instabilen Teilchen auch außerhalb des Gleichgewichts ermöglichen. Diese Bestandteile bilden die Basis des Transportmodells Parton-Hadron-String Dynamics (PHSD), welches daher ein geeignetes ’Instrument’ ist um die verschiedenen Phasen einer Schwerionenkollision zu analysieren, egal ob die verschiedenen Formen der Materie im Gleichgewicht sind oder nicht.
In dieser Arbeit wird zunächst die Quantenchromodynamik (QCD) vorgestellt und erklärt, wie diese Theorie im Laufe der Jahre entwickelt wurde um ein wichtiger Bestandteil des Standardmodells der Teilchenphysik zu werden. Wir werden weiterhin die verbleibenden Herausforderungen in unserem Verständnis der QCD vorstellen, die sich primär auf das Phasendiagramm der stark wechselwirkenden Materie konzentrieren.
Im zweiten Kapitel untersuchen wir die Nichtgleichgewichts-Feldtheorie und die damit verbundenen Techniken - wie die Keldysh-Kontur - zur Beschreibung der Green’schen Funktionen als wesentlichen Freiheitsgrade. Wir leiten die Evolutionsgleichung für die Green’schen Funktionen her, d. h. die Kadanoff Baym-Gleichungen am Beispiel einer skalaren Feldtheorie.
Im nächsten Kapitel wird das Transportmodell Parton-Hadron-String Dynamics (PHSD), welches die Anwendung der verallgemeinerten Transportgleichungen zur Beschreibung relativistischer Schwerionenkollisionen darstellt, vorgestellt.
Wir beginnen im Kapitel 4 mit der Untersuchung der Nichtgleichgewichtseigenschaften des Quark-Gluon-Plasmas, welches bei relativistischen Schwerionenkollisionen erzeugt wird. Zu diesem Zweck vergleichen wir die Quark-Gluon-Plasmaentwicklung aus dem PHSD mit einem viskosen hydrodynamischen Modell, bei dem ein lokales kinetisches und chemisches Gleichgewicht angenommen wird.
Im Kapitel 5 konzentrieren wir uns auf das frühe Vorgleichgewichtsstadium ultra-relativistischer Schwerionenkollisionen und insbesondere auf die Freiheitsgrade der QGP-Phase in diesem Stadium. Wir untersuchen die Auswirkungen eines QGP, welches anfänglich entweder aus einem System aus massiven Gluonen (Szenario I) oder alternativ aus Quarks und Antiquarks (Szenario II) besteht. Das nächste Kapitel wird ebenfalls die Produktion von Teilchen im Frühstadium von Schwerionenkollisionen behandeln, jedoch bei niedrigeren Kollisionsenergien. Hier wird eine mikroskopische Beschreibung des K+/pi+-Verhältnisses im Vordergrund stehen, d. h. die Erklärung des Maximums in diesem Verhältnis bei etwa 30 A GeV ("Horn") in zentralen Au+Au (oder Pb+Pb) Kollisionen. Insbesonders werden wir die Modifikation des String-Fragmentierungsprozesses (über den Schwinger-Mechanismus) in einer Umgebung mit hoher hadronischer Dichte aufgrund der teilweisen Wiederherstellung der chiralen Symmetrie untersuchen.
In Kapitel 7 erweitern wir das Parton-Hadron-String Dynamics (PHSD)-Transportmodell im partonischen Sektor, indem wir explizit die totalen und differentiellen partonischen Streuungsquerschnitte als Funktion der Temperatur T und des baryochemischen Potentials μB berechnen auf der Basis der effektiven Propagatoren und Kopplungen des Dynamical QuasiParticle Models (DQPM), welches auch die generelle Zeitentwicklung der partonischen Freiheitsgrade beschreibt. Wir finden nur eine sehr bescheidene Änderung von n/s mit dem baryonchemischen Potential μB in Abhängigkeit von der skalierten Temperatur T/Tc(μB). Dies gilt auch für eine Vielzahl von hadronischen Observablen aus zentralen A+A Kollisionen im Energiebereich von 5 GeV < vsNN < 200 GeV bei der Implementierung der differentiellen Querschnitte in das PHSD-Modell. Da wir in Schwerionen-Observablen nur kleine Spuren einer μB-Abhängigkeit finden - obwohl die effektiven Partonenmassen und Kollisionsbreiten sowie deren Partonenquerschnitte eindeutig von μB abhängen - impliziert dies, dass man eine beträchtliche Partonendichte und ein großes Raum-Zeit-QGP-Volumen zur Untersuchung der Dynamik in der partonischen Phase benötigt. Diese Bedingungen sind nur bei hohen Kollisionsenergien erfüllt, bei denen μB jedoch eher niedrig ist. Wenn andererseits die Kollisionsenergie verringert und somit μB erhöht wird, wird die hadronische Phase dominant und dementsprechend wird es zunehmend schwieriger, Signale aus der Partonendynamik auf der Basis von "Bulk"-Observablen zu extrahieren.
High-energetic heavy-ion collisions offer the unique opportunity to produce and to study dense nuclear matter in the laboratory. The future Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, will provide beams of heavy nuclei up to kinetic energies of 11 GeV/nucleon. At these energies, the nuclear matter in the collision zone of two nuclei will be compressed to densities of up to 5 − 10 times the saturation density of atomic nuclei, similar to matter densities existing in the core of massive neutron stars. Under those conditions, nucleons are expected to melt and form a new state of matter, which consists of quarks and gluons, the so called Quark-Gluon Plasma (QGP). The search for such a phase transition from hadronic to partonic matter, and the exploration of the nuclear matter equation-of-state at high densities are the major goals of heavy ion experiments worldwide.
The observables, which are proposed to probe the properties of dense nuclear matter and possible phase transitions, include multi-strange hyperons, antibaryons, lepton pairs, collective flow of identified particles, fluctuations and correlations of various particles, particles containing charm quarks, and hypernuclei. These observables have to be measured in multi-dimensions, i.e. as function of collision centrality, rapidity, transverse momentum, energy, emission angle, etc., which requires extremely high statistics. Moreover, some of these particles are produced very rarely.
Therefore, the Compressed Baryonic Matter (CBM) experiment at FAIR is designed to run at collision rates of up to 10 MHz, in order to perform measurements with unprecedented precision. Due to the complicated decay topology of many observables, no hardware trigger can be applied, and the data have to be analysed online in order to filter out the interesting events.
This strategy requires free-streaming read-out electronics, which provides time stamps to all detector signals, a high performance computer center, and high-speed reconstruction algorithms, which provide an online track and event reconstruction based on time and position information of the detector hits (”4-D“ reconstruction).
The core detector of the CBM experiment is the Silicon Tracking System (STS). The main task of the STS is to provide track reconstruction and momentum de- termination of charged particles originating from beam-target interactions. To fulfil the whole tasks the STS is located in the large gap of a superconducting dipole magnet with a bending power of 1 Tm providing momentum measurements for charged particles. The STS comprises 8 detector stations, which are positioned from 30 cm to 100 cm downstream the target. The corresponding active area of the stations grows up from 40×50 cm 2 up to 100×100 cm 2 with a totalarea of 4 m2. The silicon double-sided sensors exhibit 1024 strips on each side with a stereo angle at p-side of 7.5 ◦ and a strip pitch of 58 μm. The strip length ranges from 2 cm for sensors located in a close vicinity to the beam axis, up to 12 cm for other sensors where the flux of the reaction products drops down substantially. In total, the STS consist of 896 sensors mounted on 106 detector ladders. The detector readout electronics dissipates 40 kW and will be equipped with a CO 2 bi-phase cooling system. The detector including electronics will be mounted in a thermal enclosure to allow for sensor operation at below −5 ◦ C which minimizes radiation induced leakage currents.
The task of the STS is to measure the trajectories of up to 800 charged particles per collision with an efficiency of more than 95% and a momentum resolution of 1 − 2%. In order to guarantee the required performance over the full lifetime of the CBM experiment, the detector system has to have a low material budget, a high granularity, a high signal-to-noise (SNR) ratio, and a high radiation tolerance. As a result of optimisation studies, the STS consists of double-sided silicon microstrip sensors, about 300 μm thick, which have to provide a SNR ratio of more than 10, even after radiation with the expected equivalent lifetime fluence of 10 14 1 MeV n eq cm −2.
This thesis is devoted to the characterization of double-sided silicon microstrip sensors with an emphasis on investigation of their radiation hardness. Different prototypes of double sided silicon sensors produced by two vendors have been irradiated by 23 MeV protons up to the double life time fluence for the CBM experiment (2 × 10 14 1 MeV n eq cm −2 ).
The sensor properties have been characterised before and after irradiation. It was found, that after irradiation with a double lifetime fluence the leakage current increased 1000 times, which results in an increased shot noise. Moreover, the relative charge collection efficiency of irradiated with respect to non-irradiated sensors drops down to 85% for the lifetime equivalent fluence, and down to 73% for the double lifetime fluence, both for the p-side and n-side. For non-irradiated sensors the SNR was found to be in the range of 20 − 25, whereas for irradiated sensors it dropped down to 12 − 17.
In addition to the sensor characterization, a part of this thesis was devoted to the optimisation of the sensor readout scheme. In order to investigate the possible increase of SNR, and to reduce the number of readout channels in the outer aperture of STS, three versions of routing lines have been realized for the p-side readout of the sensor prototype, and have been tested in the laboratory and under beam conditions.
The tests have been performed with different inclination angles between beam direction and sensor surface, corresponding to the polar angle acceptance of the CBM experiment, which is from 2.5 ◦ to 25 ◦.
As a result of the studies carried out in this thesis work, the radiation hardness of the double-sided silicon microstrip sensors developed for the CBM STS detector was confirmed. Also the advantage of individual read-out of sensor channels in the lateral regions of the detector was verified. This allowed to start the tendering process for sensor series production in industry, an important step towards the construction of the detector in the coming years.
The influence of temperature is regarded as particularly important for a structural health monitoring system based on ultrasonic guided waves. Since the temperature effect causes stronger signal changes than a typical defect, the former must be addressed and compensated for reliable damage assessment. Development of new temperature compensation techniques as well as the comparison of existing algorithms require high-quality benchmark measurements. This paper investigates a carbon fiber reinforced plastic (CFRP) plate that was fully characterized in previous research in terms of stiffness tensor and guided wave propagation. The same CFRP plate is used here for the analysis of the temperature effect for a wide range of ultrasound frequencies and temperatures. The measurement data are a contribution to the Open Guided Waves (OGW) platform: http://www.open-guided-waves.de. The technical validation includes initial results on the analysis of phase velocity variations with temperature and exemplary damage detection results using state-of-the-art signal processing methods that aim to suppress the temperature effect.
The changing shape of the rapidity spectrum of net protons over the SPS energy range is still lacking theoretical understanding. In this work, a model for string excitation and string fragmentation is implemented for the description of high energy collisions within a hadronic transport approach. The free parameters of the string model are tuned to reproduce the experimentally measured particle production in proton-proton collisions. With the fixed parameters we advance to calculations for heavy ion collisions, where the shape of the proton rapidity spectrum changes from a single peak to a double peak structure with increasing beam energy in the experiment. We present calculations of proton rapidity spectra at different SPS energies in heavy ion collisions. Qualitatively, a good agreement with the experimental findings is obtained. In a future work, the formation process of string fragments will be studied in detail aiming to quantitatively reproduce the measurement.
The Projectile Spectator Detector (PSD) of the CBM experiment at the future FAIR facility is a compensating lead-scintillator calorimeter designed to measure the energy distribution of the forward going projectile nucleons and nuclei fragments (reaction spectators) produced close to the beam rapidity. The detector performance for the centrality and reaction plane determination is reviewed based on Monte-Carlo simulations of gold-gold collisions by means of four different heavy-ion event generators. The PSD energy resolution and the linearity of the response measured at CERN PS for the PSD supermodule consisting of 9 modules are presented. Predictions of the calorimeter radiation conditions at CBM and response measurement of one PSD module equipped with neutron irradiated MPPCs used for the light read out are discussed.
Light-matter interaction in the strong coupling regime is of profound interest for fundamental quantum optics, information processing and the realization of ultrahigh-resolution sensors. Here, we report a new way to realize strong light-matter interaction, by coupling metamaterial plasmonic "quasi-particles" with photons in a photonic cavity, in the terahertz frequency range. The resultant cavity polaritons exhibit a splitting which can reach the ultra-strong coupling regime, even with the comparatively low density of quasi-particles, and inherit the high Q-factor of the cavity despite the relatively broad resonances of the Swiss-cross and split-ring-resonator metamaterials used. We also demonstrate nonlocal collective interaction of spatially separated metamaterial layers mediated by the cavity photons. By applying the quantum electrodynamic formalism to the density dependence of the polariton splitting, we can deduce the intrinsic transition dipole moment for single-quantum excitation of the metamaterial quasi-particles, which is orders of magnitude larger than those of natural atoms. These findings are of interest for the investigation of fundamental strong-coupling phenomena, but also for applications such as ultra-low-threshold terahertz polariton lasing, voltage-controlled modulators and frequency filters, and ultra-sensitive chemical and biological sensing.
We study how the mass and magnetic moment of the quarks are dynamically generated in nonequilibrium quark matter. We derive the equal-time transport and constraint equations for the quark Wigner function in a magnetized quark model and solve them in the semi-classical expansion. The quark mass and magnetic moment are self-consistently coupled to the Wigner function and controlled by the kinetic equations. While the quark mass is dynamically generated at the classical level, the quark magnetic moment is a pure quantum effect, induced by the quark spin interaction with the external magnetic field.
We present a systematic study on the influence of spatial correlations between the proton constituents, in our case gluonic hot spots, their size and their number on the symmetric cumulant SC(2,3), at the eccentricity level, within a Monte Carlo Glauber framework [J.L. Albacete, H. Petersen, A. Soto-Ontoso, Symmetric cumulants as a probe of the proton substructure at LHC energies, Phys. Lett. B778 (2018) 128–136. arXiv:1707.05592, doi:10.1016/j.physletb.2018.01.011]. When modeling the proton as composed by 3 gluonic hot spots, the most common assumption in the literature, we find that the inclusion of spatial correlations is indispensable to reproduce the negative sign of SC(2,3) in the highest centrality bins as dictated by data. Further, the subtle interplay between the different scales of the problem is discussed. To conclude, the possibility of feeding a 2+1D viscous hydrodynamic simulation with our entropy profiles is exposed.
The diffusive behavior of macromolecules in solution is a key factor in the kinetics of macromolecular binding and assembly, and in the theoretical description of many experiments. Experiments on high-density protein solutions have found that a slow down of the diffusion dynamics is larger than expected from colloidal theory for non-interaction hard-spheres. It has also been shown that the rotational diffusion anisotropy in high-density protein solutions is larger than in dilute ones. High-density protein solutions are a complex fluid that is different from the neat fluid assumption used in the hydrodynamic theory. It is therefore important to have methods to accurately calculate the translational and rotational diffusion tensor from simulations as well as simulation algorithms to explore high-density solutions.
Simulations provide a powerful tool to study diffusion in complex fluids. They can be used to study the macroscopic and microscopic effects of complex fluids on the diffusive behavior. There has been already a lot of work done to accurately simulate diffusion and to determine the diffusion coefficients from simulations.
The translational diffusion of molecules in simple and complex liquids can be determined with high accuracy from simulations. This is not yet the case for rotational diffusion. Existing algorithms to calculate the rotational diffusion coefficients from simulations make assumptions about the shape of the protein or only work at short times. For the simulation of diffusive behavior of macromolecules two options exist today. An all-atom integrator with explicit solvent molecules or coarse-grained (CG) simulations with an implicit solvent. CG simulations of dynamic behavior with implicit solvent are also called Brownian dynamics (BD) simulations. For the CG simulations the Ermak-McCammon algorithm is often used to solve the underlying Langevin equation. The algorithm is an extension of the Euler-Maruyama integrator to include translation and rotation in three dimensions. This algorithm only correctly reproduces the equilibrium probability for short time-steps and the error depends linearly on the time-step. It has been shown that Monte Carlo based algorithms can produce BD for translational dynamics, when appropriately parametrized. The advantage of Monte Carlo based algorithm is that they will reproduce the correct equilibrium distribution independent of the chosen time-step. This in return allows choosing larger time-steps in simulations. The aim of this thesis is to develop novel´methods to accurately determine the rotational diffusion coefficient from simulations and extend existing Monte Carlo algorithms to include rotational dynamics.
The first project addresses the question of how to accurately determine the rotational diffusion coefficients from simulations. We develop a quaternion based method to calculate the rotational diffusion tensor from simulations and a theory for the effects of periodic boundary conditions (PBC) on the rotational diffusion coefficient in simulations.
Our method for calculating rotational diffusion coefficients is based on the quaternion covariances from Favro for a freely rotating rigid molecule. The covariances as formulated by Favro are only valid in the principal coordinate system (PCS) of the rotation diffusion tensor. The covariances can be generalized for an arbitrary reference coordinate system (RCS), i.e., a simulation, given the principle axes of the rotational diffusion tensor in the RCS. We show that no prior knowledge of the diffusion tensor and its principal axes is required to calculate the generalized covariances from simulations using common root-mean-square distance (RMSD) procedures. We develop two methods to fit the covariances calculated from simulations to our generalized equations to fit the rotational diffusion tensor. In the first method we minimize the sum of the squared error deviations between model and simulation data. For this six dimensional optimization we use a simulated annealing algorithm. Alternatively the rotational diffusion tensor can also be determined from a eigenvalue decomposition of covariance after integration. To minimize the effects of sampling noise in the integration we first apply a Laplace-transformation to smooth the covariances at large times. For ideal sampling the resulting rotational diffusion coefficient should be independent of the value of the Laplace variable. In practice, however, the best results are achieved using a value close to the inverse autocorrelation time of the rotational motion.
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48Si: An atypical nucleus?
(2019)
Using the relativistic Hartree–Fock Lagrangian PKA1, we investigate the properties of the exotic nucleus 48Si, which is predicted to be an atypical nucleus characterized by i) the onset of doubly magicity, ii) its location at the drip line, iii) the presence of dual semi-bubble structure (distinct central depletion in both of neutron and proton density profiles) in the ground state, and iv) the occurrence of pairing reentrance at finite temperature. While not being new for each, these phenomena are found to simultaneously occur in 48Si. For instance, the dual semi-bubble structure reduces the spin–orbit splitting of low-ℓ orbitals and upraises the s orbitals, leading therefore to distinct N=34 and Z=14 magic shells in 48Si. Consequently, the doubly magicities provide extra stability for such extreme neutron-rich system at the drip line. Associating with the neutron shell N=34 and continuum above, the pairing correlations are reengaged interestingly at finite temperature. Theoretical nuclear modelings are known to be poorly predictive in general, and we asset our confidence in the prediction of our modeling on the fact that the predictions of PKA1 in various regions of the nuclear chart have systematically been found correct and more specifically in the region of pf shell. Whether our predictions are confirmed or not, 48Si provides a concrete benchmark for the understanding of the nature of nuclear force.
Lattice QCD investigation of a doubly-bottom b̄b̄ud tetraquark with quantum numbers I(JP) = 0(1⁺)
(2019)
We use lattice QCD to investigate the spectrum of the ¯𝑏¯𝑏𝑢𝑑 four-quark system with quantum numbers 𝐼(𝐽𝑃)=0(1+). We use five different gauge-link ensembles with 2+1 flavors of domain-wall fermions, including one at the physical pion mass, and treat the heavy ¯𝑏 quark within the framework of lattice nonrelativistic QCD. Our work improves upon previous similar computations by considering in addition to local four-quark interpolators also nonlocal two-meson interpolators and by performing a Lüscher analysis to extrapolate our results to infinite volume. We obtain a binding energy of (−128±24±10) MeV, corresponding to the mass (10476±24±10) MeV, which confirms the existence of a ¯𝑏¯𝑏𝑢𝑑 tetraquark that is stable with respect to the strong and electromagnetic interactions.
We present a model for the autonomous and simultaneous learning of active binocular and motion vision. The model is based on the Active Efficient Coding (AEC) framework, a recent generalization of classic efficient coding theories to active perception. The model learns how to efficiently encode the incoming visual signals generated by an object moving in 3-D through sparse coding. Simultaneously, it learns how to produce eye movements that further improve the efficiency of the sensory coding. This learning is driven by an intrinsic motivation to maximize the system's coding efficiency. We test our approach on the humanoid robot iCub using simulations. The model demonstrates self-calibration of accurate object fixation and tracking of moving objects. Our results show that the model keeps improving until it hits physical constraints such as camera or motor resolution, or limits on its internal coding capacity. Furthermore, we show that the emerging sensory tuning properties are in line with results on disparity, motion, and motion-in-depth tuning in the visual cortex of mammals. The model suggests that vergence and tracking eye movements can be viewed as fundamentally having the same objective of maximizing the coding efficiency of the visual system and that they can be learned and calibrated jointly through AEC.
73Ge(n, γ ) cross sections were measured at the neutron time-of-flight facility n_TOF at CERN up to neutron energies of 300 keV, providing for the first time experimental data above 8 keV. Results indicate that the stellar cross section at kT = 30 keV is 1.5 to 1.7 times higher than most theoretical predictions. The new cross sections result in a substantial decrease of 73Ge produced in stars, which would explain the low isotopic abundance of 73Ge in the solar system.
This thesis is a summary of existing and upcoming publications, with a focus on high order methods in numerical relativity and general relativistic flows. The text is structed in five chapters. In the first three ones, the ADER-DG technique and its application to the Einstein-Euler equations is introduced. Novel formulations for both the Einstein equations in the 3+1 split as well as the general relativistic magnetohydrodynamics (GRMHD) had to be derived. The first order conformal and covariant Z4 formulation of Einstein equations (FO-CCZ4) is proposed and proven to be strongly hyperbolic. Together with the fluid equations of general relativistic magnetohydodynamics (GRMHD), a number of benchmark scenarios is presented to show both the correctness of the PDEs as well as the applicability of the numerical scheme.
As an application in astrophysics, a general-relativistic study of the treshold mass for a prompt-collapse of a binary neutron star merger with realistic nuclear equation of states has been carried out. A nonlinear universal relation between the treshold mass and the maximum compactness is found. Furthermore, by taking recent measurements of GW170817 into account, lower limits on the stellar radii for any mass can be given.
Furthermore, an (unpaired) work in quantum mechanical black hole engineering is presented. Higher dimensional extensions of generalized Heisenberg’s uncertainty principle (GUP) are studied. A number of new phenomenology is found, such as the existence of a conical singularity which mimics the effect of a gravitational monopole on short scale and that of a Schwarzschild black hole at a large scale, as well as oscillating Hawking temperatures which we call "lighthouse effect". All results are consistent with the self complete paradigm and a cold evaporation endpoint remnant.