arXiv subjects

W. C. Haxton

Publications and source records attributed to W. C. Haxton.

At least 37 records · Page 2Linked to original sources

arXiv2018

Particle-Hole Mirror Symmetries around the Half-Filled Shell: The Quantum Numbers and Algebraic Structure of Composite Fermions

Composite fermions (CFs) of the fractional quantum Hall effect are described as spherical products of electron and vortex spinors, built from underlying L=1/2 ladder operators aligned so that the spinor angular momenta Le and Lv are maximal. We identify the CF's quantum numbers as the angular momentum L in (L_e L_v)L, its magnetic projection m_L, the electron number N, with L_v={N-1)/2, and magnetic ν-spin, m_ν=L_e-L_v. Translationally invariant FQHE states are formed by filling p subshells with their respective CFs, in order of ascending L for fixed L_e and L_v, beginning with the lowest allowed value, L=|m_ν|. We show that this wave function has an exactly equivalent hierarchical form. FQHE states can be grouped into ν-spin multiplets mirror symmetric around m_ν=0, with N held constant. Electron particle-hole conjugation with respect to this vacuum is identified as the mirror symmetry relating FQHE states of the same N but distinct fillings ν= p/(2p+1} and p/( 2p-1). Alternatively, mirror symmetric ν-spin multiplets can be constructed in which the magnetic field strength is held fixed: the valence states are electron particle-vortex hole excitations. Particle-hole symmetry -- relating the N-particle FQHE state of filling ν=p/(2p+1} to the $\bar{N}$-particle state of filling {p+1)/(2p+1} -- is shown to be equivalent to electron-vortex exchange. In this construction $\bar{N}$-N CFs of the higher density state occupy an extra zero-mode subshell. We link this structure, familiar from supersymmetric quantum mechanics, to the CF Pauli Hamiltonian, which we show is isospectral, quadratic in the ν-spin raising and lowering operators, and four-fold degenerate. On linearization, it takes a Dirac form similar to that found in the integer quantum Hall effect (IQHE).

cond-mat.str-el↗

arXiv2017

A New Paradigm for Hadronic Parity Nonconservation and its Experimental Implications

For decades the primary experimental goal in studies of hadronic parity nonconservation (PNC) has been the isolation of the isovector weak nucleon-nucleon interaction, expected to be dominated by long-range pion exchange and enhanced by the neutral current. In meson-exchange descriptions this interaction together with an isoscalar interaction generated by rho and omega exchange dominate most observables. Consequently these two amplitudes have been used to compare and check the consistency of the field's experiments. Yet to date, despite sensitive searches like that performed with 18F, no evidence for isovector hadronic PNC has been found. Here we argue, based on recent large-Nc treatments and new global analyses, that the emphasis on isovector hadronic PNC was misplaced. Large-Nc provides an alternative and theoretically better motivated simplification of effective field theories (EFTs) of hadronic PNC, separating the five low-energy constants (LECs) into two of leading order (LO), and three others that are NNLO. This scheme pivots the isospin coordinates we have traditionally used, placing one dominant axis in the isoscalar plane, and a second along the isotensor direction. We show that this large-Nc LEC hierarchy accurately describes all existing data on hadronic PNC, and we discuss opportunities to further test the predicted large-Nc hierarchy of LECs, illustrating the kind of analyses experimentalists can use to better constrain the LO theory and to determine the size of NNLO corrections.

nucl-th↗

arXiv2016

Evidence from stable isotopes and Be-10 for solar system formation triggered by a low-mass supernova

About 4.6 billion years ago, some event disturbed a cloud of gas and dust, triggering the gravitational collapse that led to the formation of the solar system. A core-collapse supernova, whose shock wave is capable of compressing such a cloud, is an obvious candidate for the initiating event. This hypothesis can be tested because supernovae also produce telltale patterns of short-lived radionuclides, which would be preserved today as isotopic anomalies. Previous studies of the forensic evidence have been inconclusive, finding a pattern of isotopes differing from that produced in conventional supernova models. Here we argue that these difficulties either do not arise or are mitigated if the initiating supernova was a special type, low in mass and explosion energy. Key to our conclusion is the demonstration that short-lived Be-10 can be readily synthesized in such supernovae by neutrino interactions, while anomalies in stable isotopes are suppressed.

astro-ph.SR↗

arXiv2016

Nuclear Physics without High-Momentum Potentials: Direct Construction of the Effective Interaction from Scattering Observables

The standard approach to nuclear physics encodes phase shift information in an NN potential, then decodes that information in forming an effective interaction, appropriate to a low-momentum Hilbert space. Here we show that it is instead possible to construct the effective interaction directly from continuum phase shifts and mixing angles, eliminating all reference to a high momentum potential. The theory is rapidly convergent and well behaved, yielding sub-keV accuracy.

nucl-th↗

arXiv2015

Composite Fermions and the First-Landau-Level Fine Structure of the Fractional Quantum Hall Effect

A set of scalar operators are employed to generate explicit representations of both hierarchy states (e.g., the series of fillings 1/3, 2/5, 3/7, ... ) and their conjugates (fillings 1, 2/3, 3/5, ...) as non-interacting quasi-electrons filling fine-structure sub-shells within the FLL. This yields, for planar and spherical geometries, a quasi-electron representation of the incompressible FLL state of filling p/(2p +1) in a magnetic field of strength B that is algebraically identical to the IQHE state of filling p in a magnetic field of strength B/(2p+1). The construction provides a precise definition of the quasi-electron/composite fermion that differs in some respects from common descriptions: they are eigenstates of L,Lz; they and the FLL subshells they occupy carry a third index I that is associated with breaking of scalar pairs; they absorb in their internal wave functions one, not two, units of magnetic flux; and they share a common, simple structure as vector products of a spinor creating an electron and one creating magnetic flux. We argue that these properties are a consequence of the breaking of the degeneracy of noninteracting electrons within the FLL by the scale-invariant Coulomb potential. We discuss the sense in which the wave function construction supports basic ideas of both composite fermion and hierarchical descriptions of the FQHE. We describe symmetries of the quasi-electrons at half filling, where a deep Fermi sea of quasi-electrons forms, and the quasi-electrons take on Majorana and pseudo-Dirac characters. Finally, we show that the wave functions can be viewed as fermionic excitations of the bosonic half-filled shell, producing at half filling an operator that differs from but plays the same role as the Pfaffian.

cond-mat.str-el↗

arXiv2015

Nuclear structure aspects of spin-independent WIMP scattering off xenon

We study the structure factors for spin-independent WIMP scattering off xenon based on state-of-the-art large-scale shell-model calculations, which are shown to yield a good spectroscopic description of all experimentally relevant isotopes. Our results are based on the leading scalar one-body currents only. At this level and for the momentum transfers relevant to direct dark matter detection, the structure factors are in very good agreement with the phenomenological Helm form factors used to give experimental limits for WIMP-nucleon cross sections. In contrast to spin-dependent WIMP scattering, the spin-independent channel, at the one-body level, is less sensitive to nuclear structure details. In addition, we explicitly show that the structure factors for inelastic scattering are suppressed by ~ 10^{-4} compared to the coherent elastic scattering response. This implies that the detection of inelastic scattering will be able to discriminate clearly between spin-independent and spin-dependent scattering. Finally, we provide fits for all calculated structure factors.

nucl-th↗

arXiv2014

Model-independent Analyses of Dark-Matter Particle Interactions

A model-independent treatment of dark-matter particle elastic scattering has been developed, yielding the most general interaction for WIMP-nucleon low-energy scattering, and the resulting amplitude has been embedded in the nucleus, taking into account the selection rules imposed by parity and time-reversal. One finds that, in contrast to the usual spin-independent/spin-dependent (SI/SD) formulation, the resulting cross section contains six independent nuclear response functions, three of which are associated with possible velocity-dependent interactions. We find that current experiments are four orders of magnitude more sensitive to derivative couplings than is apparent in the standard SI/SD treatment, which necessarily associates such interactions with cross sections proportional to the square of the WIMP velocity relative to the nuclear center of mass.

nucl-th↗

arXiv2013

White Paper: Measuring the Neutrino Mass Hierarchy

This white paper is a condensation of a report by a committee appointed jointly by the Nuclear Science and Physics Divisions at Lawrence Berkeley National Laboratory (LBNL). The goal of this study was to identify the most promising technique(s) for resolving the neutrino mass hierarchy. For the most part, we have relied on calculations and simulations presented by the proponents of the various experiments. We have included evaluations of the opportunities and challenges for these experiments based on what is available already in the literature.

hep-ex↗

arXiv2013

Model-independent WIMP Scattering Responses and Event Rates: A Mathematica Package for Experimental Analysis

The community's reliance on simplified descriptions of WIMP-nucleus interactions reflects the absence of analysis tools that integrate general theories of dark matter with standard treatments of nuclear response functions. To bridge this gap, we have constructed a public-domain Mathematica package for WIMP analyses based on our effective theory formulation. Script inputs are 1) the coefficients of the effective theory, through which one can characterize the low-energy consequences of arbitrary ultraviolet theories of WIMP interactions; and 2) one-body density matrices for commonly used targets, the most compact description of the relevant nuclear physics. The generality of the effective theory expansion guarantees that the script will remain relevant as new ultraviolet theories are explored; the use of density matrices to factor the nuclear physics from the particle physics will allow nuclear structure theorists to update the script as new calculations become available, independent of specific particle-physics contexts. The Mathematica package outputs the resulting response functions (and associated form factors) and also the differential event rate, once a galactic WIMP velocity profile is specified, and thus in its present form provides a complete framework for experimental analysis. The Mathematica script requires no a priori knowledge of the details of the non-relativistic effective field theory or nuclear physics, though the core concepts are reviewed here and in arXiv:1203.3542.

hep-ph↗

arXiv2013

Hadronic Parity Violation

The history and phenomenology of hadronic parity nonconservation (PNC) is reviewed. We discuss the current status of the experimental tests and theory. We describe a re-analysis of the asymmetry for polarized proton-proton scattering that, when combined with other experimental constraints and with a recent lattice QCD calculation of the weak pion-nucleon coupling, reveals a much more consistent pattern of PNC couplings. In particular, isoscalar coupling strengths are similar to but somewhat larger than the "best value" estimate of Donoghue, Desplanques, and Holstein, while both lattice QCD and experiment indicate a suppressed parity-nonconserving pion-nucleon coupling. We discuss the relationship between meson-exchange models of hadronic PNC and formulations based on effective theory, stressing their general compatibility as well as the challenge presented to theory by experiment, as several of the most precise measurements involve significant momentum scales. Future directions are proposed.

nucl-th↗

arXiv2013

New Primary Mechanisms for the Synthesis of Rare 9Be in Early Supernovae

We present two new primary mechanisms for the synthesis of the rare nucleus 9Be, both triggered by nu-induced production of 3H followed by 4He(3H,gamma)7Li in the He shells of core-collapse supernovae. For progenitors of ~8M_sun, 7Li(3H,n_0)9Be occurs during the rapid expansion of the shocked He shell. Alternatively, for ultra-metal-poor progenitors of ~11-15M_sun, 7Li(n,gamma)8Li(n,gamma)9Li(e^-anti-nu_e)9Be occurs with neutrons produced by 4He(anti-nu_e,e^+n)3H, assuming a hard effective anti-nu_e spectrum from oscillations (which also leads to heavy element production through rapid neutron capture) and a weak explosion (so the 9Be survives shock passage). We discuss the associated production of 7Li and 11B, noting patterns in LiBeB production that might distinguish the new mechanisms from others.

astro-ph.SR↗

arXiv2013

Neutrino Oscillations

This review summarizes recent experimental and theoretical progress in determining neutrino mixing angles and masses through neutrino oscillations. We describe the basic physics of oscillation phenomena in vacuum and matter, as well as the status of solar, reactor, atmospheric, and accelerator neutrino experiments that probe these phenomena. The results from current global analyses of neutrino parameters are given. Future efforts that may improve the precision with which these parameters are known or probe new aspects of the neutrino mixing matrix are described.

nucl-th↗

arXiv2012

Using the Standard Solar Model to Constrain Composition and S-Factors

While standard solar model (SSM) predictions depend on approximately 20 input parameters, SSM neutrino flux predictions are strongly correlated with a single model output parameter, the core temperature $T_c$. Consequently, one can extract physics from solar neutrino flux measurements while minimizing the consequences of SSM uncertainties, by studying flux ratios with appropriate power-law weightings tuned to cancel this $T_c$ dependence. We re-examine an idea for constraining the primordial C+N content of the solar core from a ratio of CN-cycle $^{15}$O to pp-chain $^8$B neutrino fluxes, showing that nonnuclear SSM uncertainties in the ratio are small and effectively governed by a single parameter, the diffusion coefficient. We point out that measurements of both CN-I cycle neutrino branches -- $^{15}$O and $^{13}$N $β$-decay -- could in principle lead to separate determinations of the core C and N abundances, due to out-of-equilibrium CN-cycle burning in the cooler outer layers of the solar core. Finally, we show that the strategy of constructing "minimum uncertainty" neutrino flux ratios can also test other properties of the SSM. In particular, we demonstrate that a weighted ratio of $^7$Be and $^8$B fluxes constrains a product of S-factors to the same precision currently possible with laboratory data.

astro-ph.SR↗

arXiv2012

Three Puzzles from Nuclear Astrophysics

I discuss three open problems in astrophysics where nuclear physics can make important contributions: the solar abundance problem, dark matter particle detection, and the origin of the r-process elements.

nucl-th↗

arXiv2012

Neutrino Astrophysics

A review of neutrino astrophysics is presented, including solar and atmospheric neutrinos; neutrino mass and oscillations; the supernova mechanism, supernova neutrino production, and associated nucleosynthesis; cosmological neutrinos and Big Bang nucleosynthesis; neutrino cooling and associated limits on neutrino properties; and high-energy astrophysical neutrinos.

nucl-th↗

arXiv2012

Solar Neutrinos: Status and Prospects

We describe the current status of solar neutrino measurements and of the theory -- both neutrino physics and solar astrophysics -- employed in interpreting measurements. Important recent developments include Super-Kamiokande's determination of the neutrino-electron elastic scattering rate for 8B neutrinos to 3%; the latest SNO global analysis in which the inclusion of low-energy data from SNO I and II significantly narrowed the range of allowed values for the neutrino mixing angle theta12; Borexino results for both the 7Be and pep neutrino fluxes, the first direct measurements constraining the rate of ppI and ppII burning in the Sun; global reanalyses of solar neutrino data that take into account new reactor results on theta13; a new decadal evaluation of the nuclear physics of the pp chain and CNO cycle defining best values and uncertainties in the nuclear microphysics input to solar models; recognition of an emerging discrepancy between two tests of solar metallicity, helioseismological mappings of the sound speed in the solar interior, and analyses of the metal photoabsorption lines based on our best current description of the Sun's photosphere; a new round of standard solar model calculations optimized to agree either with helioseismology or with the new photospheric analysis; and, motivated by the solar abundance problem, the development of nonstandard, accreting solar models, in order to investigate possible consequences of the metal segregation that occurred in the proto-solar disk. We review this progress and describe how new experiments such as SNO+ could help us further exploit neutrinos as a unique probe of stellar interiors.

astro-ph.SR↗

arXiv2011

The Impact of Recent Advances in Laboratory Astrophysics on our Understanding of the Cosmos

An emerging theme in modern astrophysics is the connection between astronomical observations and the underlying physical phenomena that drive our cosmos. Both the mechanisms responsible for the observed astrophysical phenomena and the tools used to probe such phenomena - the radiation and particle spectra we observe - have their roots in atomic, molecular, condensed matter, plasma, nuclear and particle physics. Chemistry is implicitly included in both molecular and condensed matter physics. This connection is the theme of the present report, which provides a broad, though non-exhaustive, overview of progress in our understanding of the cosmos resulting from recent theoretical and experimental advances in what is commonly called laboratory astrophysics. This work, carried out by a diverse community of laboratory astrophysicists, is increasingly important as astrophysics transitions into an era of precise measurement and high fidelity modeling.

astro-ph.IM↗

arXiv2011

FRIB Theory Users Group Report: Joint ATLAS-HRIBF-NSCL-FRIB SuperUsers Meeting 18-20 August 2011

The FRIB (Facility for Rare Isotope Beams) Theory Users Group participated in the Joint ATLAS-HRIBF-NSCL-FRIB SuperUsers Meeting, hosted by Michigan State University August 18-20, 2011. Prior to the meeting a survey of the FRIB Theory Users Group was conducted to assess the health of the low-energy nuclear theory community and to identify perceived areas of need, in anticipation of the new demands on theory that will accompany FRIB. Meeting discussions focused on survey results and on possible responses. These discussions are summarized here.

nucl-th↗