Eigenmode Projection Techniques for Magnetic Polarisabilities in Lattice QCD

The magnetic polarisability of a selection of octet baryons and the pion are calculated using lattice QCD and the background field method. Results are from 32³ x 64 dynamical QCD gauge fields with 2 + 1 flavours provided by the PACS-CS collaboration through the International Lattice Data Grid (ILDG) . These use a clover fermion action and an Iwasaki gauge action with β = 1:9 providing a physical lattice spacing of a = 0:0907(13) fm. As the application of a uniform background magnetic field renders standard gauge covariant Gaussian smeared quark operators inefficient at isolating ground state hadron energy eigenstates at non-trivial field strengths, Landau level quark propagator projection techniques are created and utilised. First the two-dimensional U(1) Laplacian eigenmodes are considered. These describe the Landau levels of a charged particle on a finite periodic lattice. Using this eigenmode projection technique, the neutron ground state energy eigenstate is isolated and hence the magnetic polarisability of the neutron calculated. These results are used to inform a chiral effective field theory analysis to produce a prediction for the magnetic polarisability of the neutron at the physical point. The chiral analysis incorporates both finite-volume effects and sea-quark-loop contributions. Wilson-like fermion actions are exposed to additive mass renormalisations; when a background magnetic field is introduced, the Wilson term causes a field-dependent renormalisation to the quark mass. This quark mass renormalisation is studied using the neutral pion mass. Herein, the clover fermion action is investigated to determine the extent to which the O(a) removal of errors suppresses the field-dependent quark mass changes. We demonstrate how a careful treatment of the nonperturbative-improvement of the clover term is required to resolve this artefact of the Wilson term. Motivated by the success of the U(1) eigenmode-projected quarkpropagator technique, a new technique utilising eigenmodes of the SU(3) x U(1) Laplacian is considered. Here both QCD and background magnetic field effects are included in the quark propagator projection. This technique is used to calculate proton, neutron, Σ⁺ and Ξ⁰ two-point correlation functions in a background magnetic field. From these, the magnetic polarisability is calculated at several quark masses enabling a chiral effective field theory analysis. The chiral effective field theory techniques established for the neutron’s magnetic polarisability are extended to the other baryons considered herein and the results are compared. Finally, using the analysis and methods of the SU(3) x U(1) quark propagator projection technique and improved clover-fermion action, the pion sector is investigated. Results for the magnetic polarisability of both the charged and neutral pions are presented. For the first time, the relativistic energy shift is used to determine the magnetic polarisabilities.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 202

Non-zero temperature study of spin 1/2 charmed baryons using lattice gauge theory

We study the behaviour of spin 1/2 charmed baryons as the temperature increases. We make use of anisotropic lattice QCD simulations with N f = 2+1 dynam- ical flavours. After determining the positive and negative par- ity ground state masses at the lowest temperature, we inves- tigate the effect of rising temperature using ratios of thermal lattice correlators with both so-called reconstructed correla- tors and with simple model correlators. This avoids difficul- ties associated with non-zero temperature fitting or spectral reconstruction. We find that temperature effects are promi- nent throughout the hadronic phase for all negative parity channels considered and for some positive parity channels. Subsequently and where possible, we determine the masses of the ground states as a function of temperature. Finally we consider the effect of chiral symmetry restoration and extract an estimate of the pseudocritical temperature from singly charmed baryonic correlators

Recent Results from the FASTSUM Collaboration

The FASTSUM Collaboration has developed a comprehensive research programme in thermal QCD using 2+1 flavour, anisotropic ensembles. In this talk, we summarise some of our recent results including thermal hadron spectrum calculations using our ``Generation 2L'' ensembles which have pion masses of 239(1) MeV. These include open charm mesons and charm baryons. We also summarise our work using the Backus Gilbert approach to determining the spectral function of the NRQCD bottomonium system. Finally, we review our determination of the interquark potential in the same system, but using our ``Generation 2'' ensembles which have heavier pion masses of 384(4) MeV.Comment: 9 pages, Contribution to the 39th International Symposium on Lattice Field theory (LATTICE2022),8th-13th August, 2022, Bonn, German

Amplification and Overexpression of Hsa-miR-30b, Hsa-miR-30d and KHDRBS3 at 8q24.22-q24.23 in Medulloblastoma

Medulloblastoma is the most common malignant brain tumour of childhood. The identification of critical genes involved in its pathogenesis will be central to advances in our understanding of its molecular basis, and the development of improved therapeutic approaches.We performed a SNP-array based genome-wide copy number analysis in medulloblastoma cell lines, to identify regions of genomic amplification and homozygous deletion, which may harbour critical disease genes. A series of novel and established medulloblastoma defects were detected (MYC amplification (n = 4), 17q21.31 high-level gain (n = 1); 9p21.1-p21.3 (n = 1) and 6q23.1 (n = 1) homozygous deletion). Most notably, a novel recurrent region of genomic amplification at 8q24.22-q24.23 was identified (n = 2), and selected for further investigation. Additional analysis by interphase fluorescence in situ hybridisation (iFISH), PCR-based mapping and SNP-array revealed this novel amplification at 8q24.22-q24.23 is independent of MYC amplification at 8q24.21, and is unique to medulloblastoma in over 800 cancer cell lines assessed from different tumour types, suggesting it contains key genes specifically involved in medulloblastoma development. Detailed mapping identified a 3Mb common minimal region of amplification harbouring 3 coding genes (ZFAT1, LOC286094, KHDRBS3) and two genes encoding micro-RNAs (hsa-miR-30b, hsa-miR-30d). Of these, only expression of hsa-miR-30b, hsa-miR-30d and KHDRBS3 correlated with copy number status, and all three of these transcripts also displayed evidence of elevated expression in sub-sets of primary medulloblastomas, measured relative to the normal cerebellum.These data implicate hsa-miR-30b, hsa-miR-30d and KHDRBS3 as putative oncogenic target(s) of a novel recurrent medulloblastoma amplicon at 8q24.22-q24.23. Our findings suggest critical roles for these genes in medulloblastoma development, and further support the contribution of micro-RNA species to medulloblastoma pathogenesis

Hadrons at high temperature: an update from the FASTSUM collaboration

We present the most recent results from the FASTSUM collaboration for hadron properties at high temperature. This includes the temperature dependence of the light and charmed meson and baryon spectrum, as well as properties of heavy quarkonia. The results are obtained using anisotropic lattices with a fixed scale approach. We also present the status of our next generation gauge ensembles.Comment: 8 pages, 8 figures. Contribution to the XVth Quark Confinement and the Hadron Spectrum, 1-6 August 2022, Stavanger, Norwa

Hadrons at high temperature: An update from the FASTSUM collaboration

We present the most recent results from the FASTSUM collaboration for hadron properties at high temperature. This includes the temperature dependence of the light and charmed meson and baryon spectrum, as well as properties of heavy quarkonia. The results are obtained using anisotropic lattices with a fixed scale approach. We also present the status of our next generation gauge ensembles

Temporal Controls of the Asymmetric Cell Division Cycle in Caulobacter crescentus

The asymmetric cell division cycle of Caulobacter crescentus is orchestrated by an elaborate gene-protein regulatory network, centered on three major control proteins, DnaA, GcrA and CtrA. The regulatory network is cast into a quantitative computational model to investigate in a systematic fashion how these three proteins control the relevant genetic, biochemical and physiological properties of proliferating bacteria. Different controls for both swarmer and stalked cell cycles are represented in the mathematical scheme. The model is validated against observed phenotypes of wild-type cells and relevant mutants, and it predicts the phenotypes of novel mutants and of known mutants under novel experimental conditions. Because the cell cycle control proteins of Caulobacter are conserved across many species of alpha-proteobacteria, the model we are proposing here may be applicable to other genera of importance to agriculture and medicine (e.g., Rhizobium, Brucella)

Regulation of antibiotic production in Actinobacteria: new perspectives from the post-genomic era

The antimicrobial activity of many of their natural products has brought prominence to the Streptomycetaceae, a family of Gram-positive bacteria that inhabit both soil and aquatic sediments. In the natural environment, antimicrobial compounds are likely to limit the growth of competitors, thereby offering a selective advantage to the producer, in particular when nutrients become limited and the developmental programme leading to spores commences. The study of the control of this secondary metabolism continues to offer insights into its integration with a complex lifecycle that takes multiple cues from the environment and primary metabolism. Such information can then be harnessed to devise laboratory screening conditions to discover compounds with new or improved clinical value. Here we provide an update of the review we published in NPR in 2011. Besides providing the essential background, we focus on recent developments in our understanding of the underlying regulatory networks, ecological triggers of natural product biosynthesis, contributions from comparative genomics and approaches to awaken the biosynthesis of otherwise silent or cryptic natural products. In addition, we highlight recent discoveries on the control of antibiotic production in other Actinobacteria, which have gained considerable attention since the start of the genomics revolution. New technologies that have the potential to produce a step change in our understanding of the regulation of secondary metabolism are also described