Hydrogen(electron-deuteron) studies of the deuteron at high squared momentum transfer

A high resolution study of the quasielastic 2 H(e, e'p)n reaction was performed in Hall A at the Thomas Jefferson Accelerator Facility in Newport News, Virginia. The measurements were performed at a central momentum transfer of : q: ∼ 2400 MeV/c, and at a central energy transfer of ω ∼ 1500 MeV, a four momentum transfer Q2 = 3.5 (GeV/c)2, covering missing momenta from 0 to 0.5 GeV/c. The majority of the measurements were performed at Φ = 180° and a small set of measurements were done at Φ = 0°. The Hall A High Resolution Spectrometers (HRS) were used to detect coincident electrons and protons, respectively. Absolute 2H(e, e'p) n cross sections were obtained as a function of the recoiling neutron scattering angle with respect to [special characters omitted]. The experimental results were compared to a Plane Wave Impulse Approximation (PWIA) model and to a calculation that includes Final State Interaction (FSI) effects. Experimental 2H(e, e'p)n cross sections were determined with an estimated systematic uncertainty of 7%. The general features of the measured cross sections are reproduced by Glauber based calculations that take the motion of the bound nucleons into account (GEA). Final State Interactions (FSI) contributions were found to depend strongly on the angle of the recoiling neutron with respect to the momentum transfer and on the missing momentum. We found a systematic deviation of the theoretical prediction of about 30%. At small &thetas; nq (&thetas;nq < 60°) the theory overpredicts the cross section while at large &thetas; nq (&thetas;nq > 80°) the theory underestimates the cross sections. We observed an enhancement of the cross section, due to FSI, of about 240%, as compared to PWIA, for a missing momentum of 0.4 GeV/c at an angle of 75°. For missing momentum of 0.5 GeV/c the enhancement of the cross section due to the same FSI effects, was about 270%. This is in agreement with GEA. Standard Glauber calculations predict this large contribution to occur at an angle of 90°. Our results show that GEA better describes the 2H(e, e'p)n reaction.

Coherent rho meson electroproduction off deuteron

QCD predicts Color Transparency (CT), which refers to nuclear medium becoming transparent to a small color neutral object produced in high momentum transfer reactions, due to reduced strong interaction. Despite several studies at BNL, SLAC, FNAL, DESY and Jefferson Lab, a definitive signal for CT still remains elusive. In this dissertation, we present the results of a new study at Jefferson Lab motivated by theoretical calculations that suggest fully exclusive measurement of coherent rho meson electroproduction off the deuteron is a favorable channel for studying CT. Vector meson production has a large cross section at high energies, and the deuteron is the best understood and simplest nuclear system. Exclusivity allows the production and propagation to be controlled separately by controlling Q 2, lf (formation length), lc (coherence length) and t. This control is important as the rapid expansion of small objects increases their interaction probability and masks CT. The CT signal is investigated in a ratio of cross sections at high t (where re-scattering is significant) to low t (where single nucleon reactions dominate). The results are presented over a Q2 range of 1 to 3 GeV2 based on the data taken with beam energy of 6 GeV.

Weak strangeness changing semi-leptonic process

We have obtained total and differential cross sections for the strangeness changing charged current weak reaction ν L + p → Λ(Σ0) + L+ using standard dipole form factors, where L stands for an electron, muon, or tau lepton, and L + stands for an positron, anti-muon or anti-tau lepton. We calculated these reactions from near threshold few hundred MeV to 8 GeV of incoming neutrino energy and obtained the contributions of the various form factors to the total and differential cross sections. We did this in support of possible experiments which might be carried out by the MINERνA collaboration at Fermilab. The calculation is phenomenologically based and makes use of SU(3) relations to obtain the standard vector current form factors and data from Λ beta decay to obtain the axial current form factor. We also made estimates for the contributions of the pseudoscalar form factor and for the F E and FS form factors to the total and differential cross sections. We discuss our results and consider under what circumstances we might extract the various form factors. In particular we wish to test the SU(3) assumptions made in determining all the form factors over a range of q2 values. Recently new form factors were obtained from recoil proton measurements in electron-proton electromagnetic scattering at Jefferson Lab. We thus calculated the contributions of the individual form factors to the total and differential cross sections for this new set of form factors. We found that the differential and total cross sections for Λ production change only slightly between the two sets of form factors but that the differential and total cross sections change substantially for Σ 0 production. We discuss the possibility of distinguishing between the two cases for the experiments planned by the MINERνA Collaboration. We also undertook the calculation for the inverse reaction e − + p → Λ + νe for a polarized outgoing Λ which might be performed at Jefferson Lab, and provided additional analysis of the contributions of the individual form factors to the differential cross sections for this case. ^

Spectroscopy of Electroproduced Light to Medium Mass Lambda Hypernuclei

The E01-011 experiment at Jefferson Laboratory (JLab) studied light-to-medium mass Λ hypernuclei via the AZ + e → [special characters omitted] + e' + K+ electroproduction reaction. Precise measurement of hypernuclear ground state masses and excitation energies provides information about the nature of hyperon-nucleon interactions. Until recently, hypernuclei were studied at accelerator facilities with intense π+ and K- meson beams. The poor quality of these beams limited the resolution of the hypernuclear excitation energy spectra to about 1.5 MeV (FWHM). This resolution is not sufficient for resolving the rich structure observed in the excitation spectra. By using a high quality electron beam and employing a new high resolution spectrometer system, this study aims to improve the resolution to a few hundred keV with an absolute precision of about 100 keV for excitation energies. In this work the high-resolution excitation spectra of [special characters omitted], and [special characters omitted] hypernuclei are presented. In an attempt to emphasize the presence of the core-excited states we introduced a novel likelihood approach to particle identification (PID) to serve as an alternative to the commonly used standard hard-cut PID. The new method resulted in almost identical missing mass spectra as obtained by the standard approach. An energy resolution of approximately 400–500 keV (FWHM) has been achieved, an unprecedented value in hypernuclear reaction spectroscopy. For [special characters omitted] the core-excited configuration has been clearly observed with significant statistics. The embedded Λ hyperon increases the excitation energies of the 11B nuclear core by 0.5–1 MeV. The [special characters omitted] spectrum has been observed with significant statistics for the first time. The ground state is bound deeper by roughly 400 keV than currently predicted by theory. Indication for the core-excited doublet, which is unbound in the core itself, is observed. The measurement of [special characters omitted] provides the first study of a d-shell hypernucleus with sub-MeV resolution. Discrepancies of up to 2 MeV between measured and theoretically predicted binding energies are found. Similar disagreement exists when comparing to the [special characters omitted] mirror hypernucleus. Also the core-excited structure observed between the major s-, p- and d-shell Λ orbits is not consistent with the available theoretical calculations. In conclusion, the discrepancies found in this study will provide valuable input for the further development of theoretical models.

A precise measurement of the two -photon exchange effect

The two-photon exchange phenomenon is believed to be responsible for the discrepancy observed between the ratio of proton electric and magnetic form factors, measured by the Rosenbluth and polarization transfer methods. This disagreement is about a factor of three at Q 2 of 5.6 GeV2. The precise knowledge of the proton form factors is of critical importance in understanding the structure of this nucleon. The theoretical models that estimate the size of the two-photon exchange (TPE) radiative correction are poorly constrained. This factor was found to be directly measurable by taking the ratio of the electron-proton and positron-proton elastic scattering cross sections, as the TPE effect changes sign with respect to the charge of the incident particle. A test run of a modified beamline has been conducted with the CEBAF Large Acceptance Spectrometer (CLAS) at Thomas Jefferson National Accelerator Facility. This test run demonstrated the feasibility of producing a mixed electron/positron beam of good quality. Extensive simulations performed prior to the run were used to reduce the background rate that limits the production luminosity. A 3.3 GeV primary electron beam was used that resulted in an average secondary lepton beam of 1 GeV. As a result, the elastic scattering data of both lepton types were obtained at scattering angles up to 40 degrees for Q2 up to 1.5 GeV2. The cross section ratio displayed an &epsis; dependence that was Q2 dependent at smaller Q2 limits. The magnitude of the average ratio as a function of &epsis; was consistent with the previous measurements, and the elastic (Blunden) model to within the experimental uncertainties. Ultimately, higher luminosity is needed to extend the data range to lower &epsis; where the TPE effect is predicted to be largest.

Microspheres for liver radiomicrospheres therapy and planning

Liver cancer accounts for nearly 10% of all cancers in the US. Intrahepatic Arterial Radiomicrosphere Therapy (RMT), also known as Selective Internal Radiation Treatment (SIRT), is one of the evolving treatment modalities. Successful patient clinical outcomes require suitable treatment planning followed by delivery of the microspheres for therapy. The production and in vitro evaluation of various polymers (PGCD, CHS and CHSg) microspheres for a RMT and RMT planning are described. Microparticles with a 30±10 µm size distribution were prepared by emulsion method. The in vitro half-life of the particles was determined in PBS buffer and porcine plasma and their potential application (treatment or treatment planning) established. Further, the fast degrading microspheres (≤ 48 hours in vitro half-life) were labeled with 68Ga and/or 99mTc as they are suitable for the imaging component of treatment planning, which is the primary emphasis of this dissertation. Labeling kinetics demonstrated that 68Ga-PGCD, 68Ga-CHSg and 68Ga-NOTA-CHSg can be labeled with more than 95% yield in 15 minutes; 99mTc-PGCD and 99mTc-CHSg can also be labeled with high yield within 15-30 minutes. In vitro stability after four hours was more than 90% in saline and PBS buffer for all of them. Experiments in reconstituted hemoglobin lysate were also performed. Two successful imaging (RMT planning) agents were found: 99mTc-CHSg and 68Ga-NOTA-CHSg. For the 99mTc-PGCD a successful perfusion image was obtained after 10 minutes, however the in vivo degradation was very fast (half-life), releasing the 99mTc from the lungs. Slow degrading CHS microparticles (> 21 days half-life) were modified with p-SCN-b-DOTA and labeled with 90 Y for production of 90Y-DOTA-CHS. Radiochemical purity was evaluated in vitro and in vivo showing more than 90% stability after 72 and 24 hours respectively. All agents were compared to their respective gold standards (99mTc-MAA for 68Ga-NOTA-CHSg and 99m Tc-CHSg; 90Y-SirTEX for 90Y-DOTA-CHS) showing superior in vivo stability. RMT and RMT planning agents (Therapy, PET and SPECT imaging) were designed and successfully evaluated in vitro and in vivo.

Proton Form Factor Puzzle and the CEBAF Large Acceptance Spectrometer (CLAS) two-photon exchange experiment

The electromagnetic form factors are the most fundamental observables that encode information about the internal structure of the nucleon. The electric (GE) and the magnetic ( GM) form factors contain information about the spatial distribution of the charge and magnetization inside the nucleon. A significant discrepancy exists between the Rosenbluth and the polarization transfer measurements of the electromagnetic form factors of the proton. One possible explanation for the discrepancy is the contributions of two-photon exchange (TPE) effects. Theoretical calculations estimating the magnitude of the TPE effect are highly model dependent, and limited experimental evidence for such effects exists. Experimentally, the TPE effect can be measured by comparing the ratio of positron-proton elastic scattering cross section to that of the electron-proton [R = σ(e +p)/σ(e+p)]. The ratio R was measured over a wide range of kinematics, utilizing a 5.6 GeV primary electron beam produced by the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab. This dissertation explored dependence of R on kinematic variables such as squared four-momentum transfer (Q2) and the virtual photon polarization parameter (&epsis;). A mixed electron-positron beam was produced from the primary electron beam in experimental Hall B. The mixed beam was scattered from a liquid hydrogen (LH2) target. Both the scattered lepton and the recoil proton were detected by the CEBAF Large Acceptance Spectrometer (CLAS). The elastic events were then identified by using elastic scattering kinematics. This work extracted the Q2 dependence of R at high &epsis;(&epsis; > 0.8) and the $&epsis; dependence of R at ⟨Q 2⟩ approx 0.85 GeV2. In these kinematics, our data confirm the validity of the hadronic calculations of the TPE effect by Blunden, Melnitchouk, and Tjon. This hadronic TPE effect, with additional corrections contributed by higher excitations of the intermediate state nucleon, largely reconciles the Rosenbluth and the polarization transfer measurements of the electromagnetic form factors.

A Measurement of the Proton Structure Function g2p at Low Q2

Experiments at Jefferson Lab have been conducted to extract the nucleon spin-dependent structure functions over a wide kinematic range. Higher moments of these quantities provide tests of QCD sum rules and predictions of chiral perturbation theory ($\chi$PT). While precise measurements of $g_{1}^n$, $g_{2}^n$, and $g_1^p$ have been extensively performed, the data of $g_2^p$ remain scarce. Discrepancies were found between existing data related to $g_2$ and theoretical predictions. Results on the proton at large $Q^2$ show a significant deviation from the Burkhardt-Cottingham sum rule, while results for the neutron generally follow this sum rule. The next-to-leading order $\chi$PT calculations exhibit discrepancy with data on the longitudinal-transverse polarizability $\delta_{LT}^n$. Further measurements of the proton spin structure function $g_2^p$ are desired to understand these discrepancies.

Experiment E08-027 (g2p) was conducted at Jefferson Lab in experimental Hall A in 2012. Inclusive measurements were performed with polarized electron beam and a polarized ammonia target to obtain the proton spin-dependent structure function $g_2^p$ at low Q$^2$ region (0.02$<$Q$^2$$<$0.2 GeV$^2$) for the first time. The results can be used to test the Burkhardt-Cottingham sum rule, and also allow us to extract the longitudinal-transverse spin polarizability of the proton, which will provide a benchmark test of $\chi$PT calculations. This thesis will present and discuss the very preliminary results of the transverse asymmetry and the spin-dependent structure functions $g_1^p$ and $g_2^p$ from the data analysis of the g2p experiment .

Radiation Dose to the Lens of the Eye from Computed Tomography Scans of the Head

While it is well known that exposure to radiation can result in cataract formation, questions still remain about the presence of a dose threshold in radiation cataractogenesis. Since the exposure history from diagnostic CT exams is well documented in a patient’s medical record, the population of patients chronically exposed to radiation from head CT exams may be an interesting area to explore for further research in this area. However, there are some challenges in estimating lens dose from head CT exams. An accurate lens dosimetry model would have to account for differences in imaging protocols, differences in head size, and the use of any dose reduction methods.

The overall objective of this dissertation was to develop a comprehensive method to estimate radiation dose to the lens of the eye for patients receiving CT scans of the head. This research is comprised of a physics component, in which a lens dosimetry model was derived for head CT, and a clinical component, which involved the application of that dosimetry model to patient data.

The physics component includes experiments related to the physical measurement of the radiation dose to the lens by various types of dosimeters placed within anthropomorphic phantoms. These dosimeters include high-sensitivity MOSFETs, TLDs, and radiochromic film. The six anthropomorphic phantoms used in these experiments range in age from newborn to adult.

First, the lens dose from five clinically relevant head CT protocols was measured in the anthropomorphic phantoms with MOSFET dosimeters on two state-of-the-art CT scanners. The volume CT dose index (CTDIvol), which is a standard CT output index, was compared to the measured lens doses. Phantom age-specific CTDIvol-to-lens dose conversion factors were derived using linear regression analysis. Since head size can vary among individuals of the same age, a method was derived to estimate the CTDIvol-to-lens dose conversion factor using the effective head diameter. These conversion factors were derived for each scanner individually, but also were derived with the combined data from the two scanners as a means to investigate the feasibility of a scanner-independent method. Using the scanner-independent method to derive the CTDIvol-to-lens dose conversion factor from the effective head diameter, most of the fitted lens dose values fell within 10-15% of the measured values from the phantom study, suggesting that this is a fairly accurate method of estimating lens dose from the CTDIvol with knowledge of the patient’s head size.

Second, the dose reduction potential of organ-based tube current modulation (OB-TCM) and its effect on the CTDIvol-to-lens dose estimation method was investigated. The lens dose was measured with MOSFET dosimeters placed within the same six anthropomorphic phantoms. The phantoms were scanned with the five clinical head CT protocols with OB-TCM enabled on the one scanner model at our institution equipped with this software. The average decrease in lens dose with OB-TCM ranged from 13.5 to 26.0%. Using the size-specific method to derive the CTDIvol-to-lens dose conversion factor from the effective head diameter for protocols with OB-TCM, the majority of the fitted lens dose values fell within 15-18% of the measured values from the phantom study.

Third, the effect of gantry angulation on lens dose was investigated by measuring the lens dose with TLDs placed within the six anthropomorphic phantoms. The 2-dimensional spatial distribution of dose within the areas of the phantoms containing the orbit was measured with radiochromic film. A method was derived to determine the CTDIvol-to-lens dose conversion factor based upon distance from the primary beam scan range to the lens. The average dose to the lens region decreased substantially for almost all the phantoms (ranging from 67 to 92%) when the orbit was exposed to scattered radiation compared to the primary beam. The effectiveness of this method to reduce lens dose is highly dependent upon the shape and size of the head, which influences whether or not the angled scan range coverage can include the entire brain volume and still avoid the orbit.

The clinical component of this dissertation involved performing retrospective patient studies in the pediatric and adult populations, and reconstructing the lens doses from head CT examinations with the methods derived in the physics component. The cumulative lens doses in the patients selected for the retrospective study ranged from 40 to 1020 mGy in the pediatric group, and 53 to 2900 mGy in the adult group.

This dissertation represents a comprehensive approach to lens of the eye dosimetry in CT imaging of the head. The collected data and derived formulas can be used in future studies on radiation-induced cataracts from repeated CT imaging of the head. Additionally, it can be used in the areas of personalized patient dose management, and protocol optimization and clinician training.

Advanced Applications of 3D Dosimetry and 3D Printing in Radiation Therapy

As complex radiotherapy techniques become more readily-practiced, comprehensive 3D dosimetry is a growing necessity for advanced quality assurance. However, clinical implementation has been impeded by a wide variety of factors, including the expense of dedicated optical dosimeter readout tools, high operational costs, and the overall difficulty of use. To address these issues, a novel dry-tank optical CT scanner was designed for PRESAGE 3D dosimeter readout, relying on 3D printed components and omitting costly parts from preceding optical scanners. This work details the design, prototyping, and basic commissioning of the Duke Integrated-lens Optical Scanner (DIOS).

The convex scanning geometry was designed in ScanSim, an in-house Monte Carlo optical ray-tracing simulation. ScanSim parameters were used to build a 3D rendering of a convex ‘solid tank’ for optical-CT, which is capable of collimating a point light source into telecentric geometry without significant quantities of refractive-index matched fluid. The model was 3D printed, processed, and converted into a negative mold via rubber casting to produce a transparent polyurethane scanning tank. The DIOS was assembled with the solid tank, a 3W red LED light source, a computer-controlled rotation stage, and a 12-bit CCD camera. Initial optical phantom studies show negligible spatial inaccuracies in 2D projection images and 3D tomographic reconstructions. A PRESAGE 3D dose measurement for a 4-field box treatment plan from Eclipse shows 95% of voxels passing gamma analysis at 3%/3mm criteria. Gamma analysis between tomographic images of the same dosimeter in the DIOS and DLOS systems show 93.1% agreement at 5%/1mm criteria. From this initial study, the DIOS has demonstrated promise as an economically-viable optical-CT scanner. However, further improvements will be necessary to fully develop this system into an accurate and reliable tool for advanced QA.

Pre-clinical animal studies are used as a conventional means of translational research, as a midpoint between in-vitro cell studies and clinical implementation. However, modern small animal radiotherapy platforms are primitive in comparison with conventional linear accelerators. This work also investigates a series of 3D printed tools to expand the treatment capabilities of the X-RAD 225Cx orthovoltage irradiator, and applies them to a feasibility study of hippocampal avoidance in rodent whole-brain radiotherapy.

As an alternative material to lead, a novel 3D-printable tungsten-composite ABS plastic, GMASS, was tested to create precisely-shaped blocks. Film studies show virtually all primary radiation at 225 kVp can be attenuated by GMASS blocks of 0.5cm thickness. A state-of-the-art software, BlockGen, was used to create custom hippocampus-shaped blocks from medical image data, for any possible axial treatment field arrangement. A custom 3D printed bite block was developed to immobilize and position a supine rat for optimal hippocampal conformity. An immobilized rat CT with digitally-inserted blocks was imported into the SmART-Plan Monte-Carlo simulation software to determine the optimal beam arrangement. Protocols with 4 and 7 equally-spaced fields were considered as viable treatment options, featuring improved hippocampal conformity and whole-brain coverage when compared to prior lateral-opposed protocols. Custom rodent-morphic PRESAGE dosimeters were developed to accurately reflect these treatment scenarios, and a 3D dosimetry study was performed to confirm the SmART-Plan simulations. Measured doses indicate significant hippocampal sparing and moderate whole-brain coverage.

Experimental Study of Storage Ring Free-Electron Laser with Novel Capabilities

The Duke Free-electron laser (FEL) system, driven by the Duke electron storage ring, has been at the forefront of developing new light source capabilities over the past two decades. In 1999, the Duke FEL demonstrated the first lasing of a storage ring FEL in the vacuum ultraviolet (VUV) region at $194$ nm using two planar OK-4 undulators. With two helical undulators added to the outboard sides of the planar undulators, in 2005 the highest FEL gain ($47.8\%$) of a storage ring FEL was achieved using the Duke FEL system with a four-undulator configuration. In addition, the Duke FEL has been used as the photon source to drive the High Intensity $\gamma$-ray Source (HIGS) via Compton scattering of the FEL beam and electron beam inside the FEL cavity. Taking advantage of FEL's wavelength tunability as well as the adjustability of the energy of the electron beam in the storage ring, the nearly monochromatic $\gamma$-ray beam has been produced in a wide energy range from $1$ to $100$ MeV at the HIGS. To further push the FEL short wavelength limit and enhance the FEL gain in the VUV regime for high energy $\gamma$-ray production, two additional helical undulators were installed in 2012 using an undulator switchyard system to allow switching between the two planar and two helical undulators in the middle section of the FEL system. Using different undulator configurations made possible by the switchyard, a number of novel capabilities of the storage ring FEL have been developed and exploited for a wide FEL wavelength range from infrared (IR) to VUV. These new capabilities will eventually be made available to the $\gamma$-ray operation, which will greatly enhance the $\gamma$-ray user research program, creating new opportunities for certain types of nuclear physics research.

With the wide wavelength tuning range, the FEL is an intrinsically well-suited device to produce lasing with multiple colors. Taking advantage of the availability of an undulator system with multiple undulators, we have demonstrated the first two-color lasing of a storage ring FEL. Using either a three- or four-undulator configuration with a pair of dual-band high reflectivity mirrors, we have achieved simultaneous lasing in the IR and UV spectral regions. With the low-gain feature of the storage ring FEL, the power generated at the two wavelengths can be equally built up and precisely balanced to reach FEL saturation. A systematic experimental program to characterize this two-color FEL has been carried out, including precise power control, a study of the power stability of two-color lasing, wavelength tuning, and the impact of the FEL mirror degradation. Using this two-color laser, we have started to develop a new two-color $\gamma$-ray beam for scientific research at the HIGS.

Using the undulator switchyard, four helical undulators installed in the beamline can be configured to not only enhance the FEL gain in the VUV regime, but also allow for the full polarization control of the FEL beams. For the accelerator operation, the use of helical undulators is essential to extend the FEL mirror lifetime by reducing radiation damage from harmonic undulator radiation. Using a pair of helical undulators with opposite helicities, we have realized (1) fast helicity switching between left- and right-circular polarizations, and (2) the generation of fully controllable linear polarization. In order to extend these new capabilities of polarization control to the $\gamma$-ray operation in a wide energy range at the HIGS, a set of FEL polarization diagnostic systems need to be developed to cover the entire FEL wavelength range. The preliminary development of the polarization diagnostics for the wavelength range from IR to UV has been carried out.

A transport beamline solution to control optically accelerated proton beams

Laser-target interaction represents a very promising field for several potential applications,
from the nuclear physics to the radiobiology. However optically accelerated particle beams are
characterized by some extreme features, not suitable for many applications. Therefore, beyond
the improvements at the laser-target interaction level, many researchers are spending their efforts
for the development of specific beam transport devices in order to obtain controlled and
reproducible output beams.In this background, the ELIMED (ELI-Beamlines MEDical applications)
project was born. Within 2017, a dedicated transport beam-line coupled with dosimetric
systems, named ELIMED, will be installed at the Extreme Light Infrastructure Beamlines
(ELI-Beamlines) facility in Prague (CZ),as a part of the ELIMAIA (ELI Multidisciplinary Applications
of laserâA ¸SIon Acceleration) beamline

Outer crust of a cold non-accreting magnetar

The outer-crust structure and composition of a cold, non-accreting magnetar are studied. We model the outer crust to be made of fully equilibrated matter where ionized nuclei form a Coulomb crystal embedded in an electron gas. The main effects of the strong magnetic field are those of quantizing the electron motion in Landau levels and of modifying the nuclear single-particle levels producing, on average, an increased binding of nucleons in nuclei present in the Coulomb lattice. The effect of a homogeneous and constant magnetic field on nuclear masses has been predicted by using a covariant density functional in which induced currents and axial deformation due to the presence of a magnetic field that breaks time-reversal symmetry have been included self-consistently in the nucleon and meson equations of motion. Although not yet observed, for Ba 1016 G both effects contribute to produce different compositions - odd-mass nuclei are frequently predicted - and to increase the neutron-drip pressure as compared to a typical neutron star. Specifically, in such a regime, the magnetic-field effects on nuclei favor the appearance of heavier nuclei at low pressures. As B increases, such heavier nuclei are also preferred up to larger pressures. For the most extreme magnetic field considered, B=1018 G, and for the models studied, almost the whole outer crust is made of 4092Zr52.

Flavour symmetries in a renormalizable SO(10) model

In the context of a renormalizable supersymmetric SO(10) Grand Unified Theory, we consider the fermion mass matrices generated by the Yukawa couplings to a 10 circle plus 120 circle plus (126) over bar representation of scalars. We perform a complete investigation of the possibilities of imposing flavour symmetries in this scenario; the purpose is to reduce the number of Yukawa coupling constants in order to identify potentially predictive models. We have found that there are only 14 inequivalent cases of Yukawa coupling matrices, out of which 13 cases are generated by 74 symmetries, with suitable n, and one case is generated by a Z(2) x Z(2) symmetry. A numerical analysis of the 14 cases reveals that only two of them-dubbed A and B in the present paper allow good fits to the experimentally known fermion masses and mixings. (C) 2016 The Authors. Published by Elsevier B.V.

Sasakian quiver gauge theories and instantons on cones over lens 5-spaces

We consider SU(3)-equivariant dimensional reduction of Yang Mills theory over certain cyclic orbifolds of the 5-sphere which are Sasaki-Einstein manifolds. We obtain new quiver gauge theories extending those induced via reduction over the leaf spaces of the characteristic foliation of the Sasaki-Einstein structure, which are projective planes. We describe the Higgs branches of these quiver gauge theories as moduli spaces of spherically symmetric instantons which are SU(3)-equivariant solutions to the Hermitian Yang-Mills equations on the associated Calabi-Yau cones, and further compare them to moduli spaces of translationally-invariant instantons on the cones. We provide an explicit unified construction of these moduli spaces as Kahler quotients and show that they have the same cyclic orbifold singularities as the cones over the lens 5-spaces. (C) 2015 The Authors. Published by Elsevier B.V.