arXiv subjects

Brian D. Serot

Publications and source records attributed to Brian D. Serot.

At least 19 recordsLinked to original sources

arXiv2013

Can neutrino-induced photon production explain the low energy excess in MiniBooNE?

This report summarizes our study of Neutral Current (NC)-induced photon production in MiniBooNE, as motivated by the low energy excess in this experiment [A. A. Aquilar-Arevalo et al. (MiniBooNE Collaboration), Phys. Rev. Lett. 98, 231801 (2007); 103, 111801 (2009)]. It was proposed that NC photon production with two anomalous photon-$Z$ boson-vector meson couplings might explain the excess. However, our computed event numbers in both neutrino and antineutrino runs are consistent with the previous MiniBooNE estimate that is based on their pion production measurement. Various nuclear effects discussed in our previous works, including nucleon Fermi motion, Pauli blocking, and the $Δ$ resonance broadening in the nucleus, are taken into account. Uncertainty due to the two anomalous terms and nuclear effects are studied in a conservative way.

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arXiv2012

Coherent Neutrinoproduction of Photons and Pions in a Chiral Effective Field Theory for Nuclei

In this paper we study coherent neutrinoproduction of photons [neutral current (NC)] and pions [charged current (CC) and NC] with $E_ν \leqslant 0.5 $ GeV. The production from nucleons and incoherent production with $E_ν \leqslant 0.5 \mathrm{GeV}$ have been studied in [B. D. Serot and X. Zhang, Phys. Rev. C 86, (2012) 015501; and X. Zhang and B. D. Serot, Phys. Rev. C 86, (2012) 035502]. These processes are relevant to the background analysis in neutrino-oscillation experiments, for example MiniBooNE [A. A. Aquilar-Arevalo et al. (MiniBooNE Collaboration), Phys. Rev. Lett. 100, 032301 (2008)]. We work in the framework of a Lorentz-covariant effective field theory (EFT), which contains nucleons, pions, the Delta (1232) ($Δ$s), isoscalar scalar ($σ$) and vector ($ω$) fields, and isovector vector ($ρ$) fields. The Lagrangian exhibits a nonlinear realization of (approximate) $SU(2)_{L} \otimes SU(2)_{R}$ chiral symmetry and incorporates vector meson dominance. In the calculation, a revised version of the so-called "optimal approximation" is applied, in which one-nucleon interaction amplitude is factorized out and its medium-modifications are included. The distortion of final pion wave function is calculated using the Eikonal approximation. In addition, we briefly mention the ambiguity of off-shell interaction amplitude. To benchmark the approximation scheme, we study coherent pion photoproduction. Our scheme is then applied to study the neutrinoproductions. In the pion photoproduction and NC photon production, we are able to address the contributions of two contact terms that are partially related to the proposed anomalous interactions involving $ω(ρ)$ $Z$ boson and photon. The calculation is focused on ${}^{12}C$ target, and can be applied to other medium-heavy nucleus.

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arXiv2012

Neutrinoproduction of Photons and Pions From Nucleons in a Chiral Effective Field Theory for Nuclei

Neutrino-induced productions (neutrinoproduction) of photons and pions from nucleons and nuclei are important for the interpretation of neutrino-oscillation experiments, as they are potential backgrounds in the MiniBooNE experiment [A. A. Aquilar-Arevalo et al. (MiniBooNE Collaboration), Phys. Rev. Lett. {\bf 100}, 032301 (2008)]. These processes are studied at intermediate energies, where the Δ(1232) resonance becomes important. The Lorentz-covariant effective field theory, which is the framework used in this series of study, contains nucleons, pions, Δs, isoscalar scalar (σ) and vector (ω) fields, and isovector vector (ρ) fields. The lagrangian exhibits a nonlinear realization of (approximate) $SU(2)_L \otimes SU(2)_R$ chiral symmetry and incorporates vector meson dominance. In this paper, we focus on setting up the framework. Power counting for vertices and Feynman diagrams is explained. Because of the built-in symmetries, the vector current is automatically conserved (CVC), and the axial-vector current is partially conserved (PCAC). To calibrate the axial-vector transition current (N $\leftrightarrow$ Δ), pion production from the nucleon is used as a benchmark and compared to bubble-chamber data from Argonne and Brookhaven National Laboratories. At low energies, the convergence of our power-counting scheme is investigated, and next-to-leading-order tree-level corrections are found to be small.

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arXiv2012

Incoherent Neutrinoproduction of Photons and Pions in a Chiral Effective Field Theory for Nuclei

We study the incoherent neutrinoproduction of photons and pions with neutrino energy E_ν $\leqslant$ 0.5 GeV. These processes are relevant to the background analysis in neutrino-oscillation experiments, for example MiniBooNE [A. A. Aquilar-Arevalo \textit{et al.} (MiniBooNE Collaboration), Phys. Rev. Lett. 100, 032301(2008)]. The calculations are carried out using a Lorentz-covariant effective field theory (EFT) which contains nucleons, pions, the Delta (1232) ($Δ$ s), isoscalar scalar ($σ$) and vector ($ω$) fields, and isovector vector ($ρ$) fields, and has SU(2)_{L} $\otimes$ SU(2)_{R} chiral symmetry realized nonlinearly. The contributions of one-body currents are studied in the local fermi gas approximation. The current form factors are generated by meson dominance in the EFT Lagrangian. The conservation of the vector current and the partial conservation of the axial current are satisfied automatically, which is crucial for photon production. The $Δ$ dynamics in nuclei, as a key component in the study, are explored. Introduced $Δ$-meson couplings explain the $Δ$ spin-orbit (S-L) coupling in nuclei, and this leads to interesting constraints on the theory. Meanwhile a phenomenological approach is applied to parametrize the $Δ$ width. To benchmark our approximations, we calculate the differential cross sections for quasi-elastic scattering and incoherent electroproduction of pions without a final state interaction (FSI). The FSI can be ignored for photon production.

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arXiv2011

Electroweak Interactions in a Chiral Effective Lagrangian for Nuclei

We have studied electroweak (EW) interactions in quantum hadrodynamics (QHD) effective field theory (EFT). The Lorentz-covariant EFT contains nucleon, pion, $Δ$, isoscalar scalar ($σ$) and vector ($ω$) fields, and isovector vector ($ρ$) fields. The lagrangian exhibits a nonlinear realization of (approximate) $SU(2)_L \otimes SU(2)_R$ chiral symmetry and incorporates vector meson dominance. First, we discuss the EW interactions at the quark level. Then we include EW interactions in QHD EFT by using the background-field technique. The completed QHD EFT has a nonlinear realization of $SU(2)_L \otimes SU(2)_R \otimes U(1)_B$ (chiral symmetry and baryon number conservation), as well as realizations of other symmetries including Lorentz-invariance, $C$, $P$, and $T$. Meanwhile, as we know, chiral symmetry is manifestly broken due to the nonzero quark masses; the $P$ and $C$ symmetries are also broken because of weak interactions. These breaking patterns are parameterized in a general way in the EFT. Moreover, we have included the $Δ$ resonance as manifest degrees of freedom in our QHD EFT, with a discussion of the irrelevance of the well-known pathologies involving high-spin fields from the modern EFT perspective. This enables us to discuss physics at the kinematics where the resonance becomes important. As a result, the effective theory uses hadronic degrees of freedom, satisfies the constraints due to QCD (symmetries and their breaking pattern), and is calibrated to strong-interaction phenomena. Applications to (anti)neutrino scattering are briefly discussed.

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arXiv2010

Weak Pion and Photon Production off Nucleons in a Chiral Effective Field Theory

Neutrino-induced pion and photon production from nucleons and nuclei are important for the interpretation of neutrino-oscillation experiments, and these processes are potential backgrounds in the MiniBooNE experiment [A. A. Aquilar-Arevalo \textit{et al.} (MiniBooNE Collaboration), Phys.\ Rev.\ Lett.\ {\bf 100}, 032301 (2008)]. Pion and photon production are investigated at intermediate energies, where the $Δ$ resonance becomes important. The Lorentz-covariant effective field theory contains nucleons, pions, Deltas, isoscalar scalar ($σ$) and vector ($ω$) fields, and isovector vector ($ρ$) fields. The lagrangian exhibits a nonlinear realization of (approximate) $SU(2)_L \otimes SU(2)_R$ chiral symmetry and incorporates vector meson dominance. Power counting for vertices and Feynman diagrams involving the $Δ$ is explained. Because of the built-in symmetries, the vector currents are automatically conserved, and the axial-vector currents satisfy PCAC. The irrelevance of so-called off-shell $Δ$ couplings and the structure of the dressed $Δ$ propagator, which has a pole only in the spin-3/2 channel, are discussed. To calibrate the axial-vector transition current $(N\! \leftrightarrow Δ)$, pion production from the nucleon is used as a benchmark and compared to bubble-chamber data from Argonne and Brookhaven National Laboratories. At low energies, the convergence of our power-counting scheme is investigated, and next-to-leading-order tree-level corrections are found to be very small.

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arXiv2009

A Field-Theoretic Parametrization of Low-Energy Nucleon Form Factors

A field-theoretic parametrization is proposed for nucleon electromagnetic form factors at momentum transfer less than 600 MeV. The parametrization is part of a larger effective field theory lagrangian that is Lorentz covariant and chirally symmetric, and that has been used to successfully describe bulk and single-particle properties of medium to heavy mass nuclei. The parametrization is based on vector meson dominance and a derivative expansion of nucleon couplings to the electromagnetic fields. At lowest order in the expansion, it is possible to fit all four parameters to modern data on the rms radii of the nucleon form factors. At next-to-leading order it is possible to fit the form factors to within a few percent up to momentum transfers of 600 MeV. The vector meson dominance contributions are crucial in this fit, since a simple expansion in powers of momentum transfer would require many, many terms to achieve comparable accuracy. The ability to fit single-nucleon form factors up to 600 MeV momentum transfer makes possible the study of two-body electromagnetic exchange currents within this effective field theory framework.

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arXiv2007

Two-loop Corrections for Nuclear Matter in a Covariant Effective Field Theory

Although one-loop calculations provide a realistic description of bulk and single-particle nuclear properties, it is necessary to examine loop corrections to develop a systematic finite-density power-counting scheme for the nuclear many-body problem when loops are included. Moreover, it is imperative to study exchange and correlation corrections systematically to make reliable predictions for other nuclear observables. One must also verify that the natural sizes of the one-loop parameters are not destroyed by explicit inclusion of many-body corrections. The loop expansion is applied to a chiral effective hadronic lagrangian; with the techniques of Infrared Regularization, it is possible to separate out the short-range contributions and to write them as local products of fields that are already present in our lagrangian. (The appropriate field variables must be re-defined at each order in loops.) The corresponding parameters implicitly include short-range effects to all orders in the interaction, so these effects need not be calculated explicitly. The remaining (long-range) contributions that must be calculated are nonlocal and resemble those in conventional nuclear-structure calculations. Calculations at the two-loop level are carried out to illustrate these techniques at finite densities and to verify that the coupling parameters remain natural when fitted to the empirical properties of equilibrium nuclear matter.

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arXiv2007

Loop Corrections and Naturalness in a Chiral Effective Field Theory

The loop expansion is applied to a chiral effective hadronic lagrangian; with the techniques of Infrared Regularization, it is possible to separate out the short-range contributions and to write them as local products of fields that are already present in our lagrangian. (The appropriate field variables must be re-defined at each order in loops.) The corresponding parameters implicitly include short-range effects to all orders in the interaction, so these effects need not be calculated explicitly. The remaining (long-range) contributions that must be calculated are nonlocal and resemble those in conventional nuclear-structure calculations. Nonlinear isoscalar scalar $(σ)$ and vector $(ω)$ meson interactions are included, which incorporate many-nucleon forces and nucleon substructure. Calculations are carried out at the two-loop level to illustrate these techniques at finite nuclear densities and to verify that the coupling parameters remain natural when fitted to the empirical properties of equilibrium nuclear matter. Contributions from the $ωN$ tensor coupling are also discussed.

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arXiv2005

Electromagnetic Interactions in a Chiral Effective Lagrangian for Nuclei

Electromagnetic (EM) interactions are incorporated in a recently proposed effective field theory of the nuclear many-body problem. Earlier work with this effective theory exhibited EM couplings that are correct only to lowest order in both the pion fields and the electric charge. The Lorentz-invariant effective field theory contains nucleons, pions, isoscalar scalar (σ) and vector (ω) fields, and isovector vector (ρ) fields. The theory exhibits a nonlinear realization of SU(2)_L \times SU(2)_R chiral symmetry and has three desirable features: it uses the same degrees of freedom to describe the currents and the strong-interaction dynamics, it satisfies the symmetries of the underlying QCD, and its parameters can be calibrated using strong-interaction phenomena, like hadron scattering or the empirical properties of finite nuclei. It has been verified that for normal nuclear systems, the effective lagrangian can be expanded systematically in powers of the meson fields (and their derivatives) and can be truncated reliably after the first few orders. The complete EM lagrangian arising from minimal substitution is derived and shown to possess the residual chiral symmetry of massless, two-flavor QCD with EM interactions. The uniqueness of the minimal EM current is proved, and the properties of the isovector vector and axial-vector currents are discussed, generalizing earlier work. The residual chiral symmetry is maintained in additional (non-minimal) EM couplings expressed as a derivative expansion and in implementing vector meson dominance. The role of chiral anomalies in the EM lagrangian is briefly discussed.

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arXiv2004

Covariant Effective Field Theory for Nuclear Structure and Currents

Recent progress in Lorentz-covariant quantum field theories of the nuclear many-body problem (quantum hadrodynamics or QHD) is discussed. The effective field theory studied here contains nucleons, pions, isoscalar scalar (σ) and vector (ω) fields, and isovector vector (ρ) fields. The theory exhibits a nonlinear realization of spontaneously broken SU(2) \times SU(2) chiral symmetry and has three desirable features: it uses the same degrees of freedom to describe the nuclear currents and the strong-interaction dynamics, it satisfies the symmetries of the underlying theory of QCD, and its parameters can be calibrated using strong-interaction phenomena, like hadron scattering or the empirical properties of finite nuclei. Moreover, it has recently been verified that for normal nuclear systems, it is possible to expand the effective lagrangian systematically in powers of the meson fields (and their derivatives) and to truncate the expansion reliably after the first few orders. Using a mean-field version of the energy functional, accurate quantitative results are obtained for the bulk and single-particle properties of medium- and heavy-mass nuclei. The importance of modern perspectives in effective field theory and density functional theory for understanding these successes of QHD is emphasized. The inclusion of hadronic electromagnetic structure and of nonanalytic terms in the energy functional is also considered briefly. Weak-interaction currents are also studied in this QHD framework. Expressions for the axial-vector current, evaluated through the first few orders in the field expansion, satisfy both PCAC and the Goldberger--Treiman relation. Moreover, the corresponding vector and axial-vector charges satisfy the familiar chiral charge algebra to all orders in the pion field.

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arXiv2003

Covariant Effective Field Theory for Nuclear Structure and Nuclear Currents

Recent progress in Lorentz-covariant quantum field theories of the nuclear many-body problem (quantum hadrodynamics or QHD) is discussed. The effective field theory studied here contains nucleons, pions, isoscalar scalar (σ) and vector (ω) fields, and isovector vector (ρ) fields. The theory exhibits a nonlinear realization of spontaneously broken SU(2)_L \times SU(2)_R chiral symmetry and has three desirable features: it uses the same degrees of freedom to describe the nuclear currents and the strong-interaction dynamics, it satisfies the symmetries of the underlying theory of QCD, and its parameters can be calibrated using strong-interaction phenomena, like hadron scattering or the empirical properties of finite nuclei. Moreover, it has recently been verified that for normal nuclear systems, it is possible to expand the effective Lagrangian systematically in powers of the meson fields (and their derivatives) and to truncate the expansion reliably after the first few orders. Using a mean-field version of the energy functional, accurate quantitative results are obtained for the bulk and single-particle properties of medium- and heavy-mass nuclei. The importance of modern perspectives in effective field theory and density functional theory for understanding these successes of QHD is emphasized. The inclusion of hadronic electromagnetic structure and of nonanalytic terms in the energy functional is also considered briefly. As a further application, weak-interaction currents are studied in the QHD framework. The axial-vector current, evaluated through the leading order in the field expansion, satisfies both PCAC and the Goldberger--Treiman relation, and the corresponding vector and axial-vector charges satisfy the familiar chiral charge algebra to all orders in the pion field.

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arXiv2003

Building Atomic Nuclei with the Dirac Equation

The relevance of the Dirac equation for computations of nuclear structure is motivated and discussed. Quantitatively successful results for medium- and heavy-mass nuclei are described, and modern ideas of effective field theory and density functional theory are used to justify them.

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arXiv2002

The Axial-Vector Current in Nuclear Many-Body Physics

Weak-interaction currents are studied in a recently proposed effective field theory of the nuclear many-body problem. The Lorentz-invariant effective field theory contains nucleons, pions, isoscalar scalar ($σ$) and vector ($ω$) fields, and isovector vector ($ρ$) fields. The theory exhibits a nonlinear realization of $SU(2)_L \times SU(2)_R$ chiral symmetry and has three desirable features: it uses the same degrees of freedom to describe the axial-vector current and the strong-interaction dynamics, it satisfies the symmetries of the underlying theory of quantum chromodynamics, and its parameters can be calibrated using strong-interaction phenomena, like hadron scattering or the empirical properties of finite nuclei. Moreover, it has recently been verified that for normal nuclear systems, it is possible to systematically expand the effective lagrangian in powers of the meson fields (and their derivatives) and to reliably truncate the expansion after the first few orders. Here it is shown that the expressions for the axial-vector current, evaluated through the first few orders in the field expansion, satisfy both PCAC and the Goldberger--Treiman relation, and it is verified that the corresponding vector and axial-vector charges satisfy the familiar chiral charge algebra. Explicit results are derived for the Lorentz-covariant, axial-vector, two-nucleon amplitudes, from which axial-vector meson-exchange currents can be deduced.

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arXiv2002

Covariant RPA in Effective Hadronic Field Theory

In an effective hadronic theory constructed to describe long-range nuclear physics, the dynamics of the vacuum can be expanded in terms with zero or a finite number of derivatives acting on the fields. Thus vacuum dynamics can always be absorbed in the (infinite number of) counterterm parameters necessarily present in the effective lagrangian. These finite parameters, which at present must be fitted to data, encode the empirical vacuum physics as well as other short-range dynamics into the effective lagrangian; in practice, only a small number of parameters must be fitted. The strength of the effective field theory (EFT) framework is that there is no need to make a concrete picture of the vacuum dynamics, as one does in a renormalizable hadronic theory. At the one-loop level, the most convenient renormalization scheme requires explicit sums over long-range (``valence'') nucleon orbitals only, thus explaining the so-called ``no-sea approximation'' used in successful covariant mean-field theory (MFT) calculations of static ground states. When excited states are studied in the random-phase approximation (RPA), the same EFT scheme dictates the inclusion of both familiar particle-hole pairs and contributions that mix valence and negative-energy single-particle Dirac wave functions. The modern EFT strategy therefore justifies and explains the omission of some explicit contributions from the negative-energy Dirac sea of nucleons, as was done to maintain conservation laws in earlier pragmatic calculations of the nuclear linear response.

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arXiv2002

Effective Field Theory for Bulk Properties of Nuclei

Recent progress in Lorentz-covariant quantum field theories of the nuclear many-body problem ({\em quantum hadrodynamics}, or QHD) is discussed. The importance of modern perspectives in effective field theory and density functional theory for understanding the successes of QHD is emphasized. The inclusion of hadronic electromagnetic structure and of nonanalytic terms in the energy functional is also considered.

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arXiv2000

Effective Field Theory in Nuclear Many-Body Physics

Recent progress in Lorentz-covariant quantum field theories of the nuclear many-body problem (quantum hadrodynamics, or QHD) is discussed. The importance of modern perspectives in effective field theory and density functional theory for understanding the successes of QHD is emphasized. To appear in: 150 Years of Quantum Many-Body Theory: A conference in honour of the 65th birthdays of John W. Clark, Alpo J. Kallio, Manfred L. Ristig, and Sergio Rosati.

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arXiv2000

Quantum Hadrodynamics: Evolution and Revolution

The underlying philosophy and motivation for quantum hadrodynamics (QHD), namely, relativistic field theories of nuclear phenomena featuring manifest covariance, have evolved over the last quarter century in response to successes, failures, and sharp criticisms. A recent revolution in QHD, based on modern effective field theory and density functional theory perspectives, explains the successes, provides antidotes to the failures, rebuts the criticisms, and focuses the arguments in favor of a covariant representation.

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