arXiv subjects

Ulf-G. Meißner

Publications and source records attributed to Ulf-G. Meißner.

At least 253 records · Page 14Linked to original sources

arXiv2018

Derivation of spontaneously broken gauge symmetry from the consistency of effective field theory II: Scalar field self-interactions and the electromagnetic interaction

We extend our study of deriving the local gauge invariance with spontaneous symmetry breaking in the context of an effective field theory by considering self-interactions of the scalar field and inclusion of the electromagnetic interaction. By analyzing renormalizability and the scale separation conditions of three-, four- and five-point vertex functions of the scalar field, we fix the two couplings of the scalar field self-interactions of the leading order Lagrangian. Next we add the electromagnetic interaction and derive conditions relating the magnetic moment of the charged vector boson to its charge and the masses of the charged and neutral massive vector bosons to each other and the two independent couplings of the theory. We obtain the bosonic part of the Lagrangian of the electroweak Standard Model as a unique solution to the conditions imposed by the self-consistency conditions of the considered effective field theory.

hep-th↗

arXiv2018

New spectrum of negative-parity doubly charmed baryons: Possibility of two quasistable states

The discovery of $Ξ_{cc}^{++}$ by the LHCb Collaboration triggers predictions of more doubly charmed baryons. By taking into account both the $P$-wave excitations between the two charm quarks and the scattering of light pseudoscalar mesons off the ground state doubly charmed baryons, a set of negative-parity spin-1/2 doubly charmed baryons are predicted already from a unitarized version of leading order chiral perturbation theory. Moreover, employing heavy antiquark-diquark symmetry the relevant low-energy constants in the next-to-leading order are connected with those describing light pseudoscalar mesons scattering off charmed mesons, which have been well determined from lattice calculations and experimental data. Our calculations result in a spectrum richer than that of heavy mesons. We find two very narrow $J^P=1/2^-$ $Ω_{cc}^P$, which very likely decay into $Ω_{cc}π^0$ breaking isospin symmetry. In the isospin-1/2 $Ξ_{cc}^P$ sector, three states are predicted to exist below 4.2~GeV with the lowest one being narrow and the other two rather broad. We suggest to search for the $Ξ_{cc}^{P}$ states in the $Ξ_{cc}^{++}π^-$ mode. Searching for them and their analogues are helpful to establish the hadron spectrum.

hep-ph↗

arXiv2018

Towards a new paradigm for heavy-light meson spectroscopy

Since 2003 many new hadrons, including the lowest-lying positive-parity charm-strange mesons ${D_{s0}^*(2317)}$ and ${D_{s1}(2460)}$, were observed that do not conform with quark model expectations. It was recently demonstrated that various puzzles in the charm meson spectrum find a natural resolution, if the SU(3) multiplets for the lightest scalar and axial-vector states, amongst them the ${D_{s0}^*(2317)}$ and the ${D_{s1}(2460)}$, owe their existence to the nonperturbative dynamics of Goldstone-Boson scattering off $D_{(s)}$ and $D^*_{(s)}$ mesons. Most importantly the ordering of the lightest strange and nonstrange scalars becomes natural. In this work we demonstrate for the first time that this mechanism is strongly supported by the recent high quality data on the ${B^-\to D^+π^-π^- }$ provided by the LHCb experiment. This implies that the lowest quark-model positive-parity charm mesons, together with their bottom counterparts, if realized in nature, do not form the ground-state multiplet. This is similar to the pattern that has been established for the scalar mesons made from light up, down and strange quarks, where the lowest multiplet is considered to be made of states not described by the quark model. In a broader view, the hadron spectrum must be viewed as more than a collection of quark model states.

hep-ph↗

arXiv2018

Test of semi-local duality in a large $N_C$ framework

In this paper we test the semi-local duality based on the method of Ref.[1] for calculating final-state interactions at varying number of colors ($N_C$). We compute the amplitudes by dispersion relations that respect analyticity and coupled channel unitarity, as well as accurately describing experiment. The $N_C$ dependence of the $ππ\toππ$ scattering amplitudes is obtained by comparing these amplitudes to the one of chiral perturbation theory. The semi-local duality is investigated by varying $N_C$. Our results show that the semi-local duality is not violated when $N_C$ is large. At large $N_C$, the contributions of the $f_2(1270)$, the $f_0(980)$ and the $f_0(1370)$ cancel that of the $ρ(770)$ in the finite energy sum rules, while the $f_0(500)$ has almost no effect. This gives further credit to the method developed in Ref.[1] for investigating the $N_C$ dependence of hadron-hadron scattering with final-state interactions. This study is also helpful to understand the structure of the scalar mesons.

hep-ph↗

arXiv2018

Neutron-proton scattering with lattice chiral effective field theory at next-to-next-to-next-to-leading order

We present a new lattice formulation of chiral effective field theory interactions with a simpler decomposition into spin channels. With these interactions the process of fitting to the empirical scattering phase shifts is simplified, and the resulting lattice phase shifts are more accurate than in previous studies. We present results for the neutron-proton system up to next-to-next-to-next-to-leading order for lattice spacings of $1.97$, $1.64$, $1.32$, and $0.99~{\rm fm}$. Our results provide a pathway to $\textit{ab initio}$ lattice calculations of nuclear structure, reactions, and thermodynamics with accurate and systematic control over the chiral nucleon-nucleon force.

nucl-th↗

arXiv2018

How (not) to renormalize integral equations with singular potentials in effective field theory

We discuss the connection between the perturbative and non-perturbative renormalization and related conceptual issues in the few-nucleon sector of the low-energy effective field theory of the strong interactions. General arguments are supported by examples from effective theories with and without pions as dynamical degrees of freedom. A quantum mechanical potential with explicitly specified short- and long-range parts is considered as an "underlying fundamental theory" and the corresponding effective field theory potential is constructed. Further, the problem of the effective field theoretical renormalization of the Skornyakov-Ter-Martyrosian equation is revisited.

nucl-th↗

arXiv2018

Interactions of Charmed Mesons with Light Pseudoscalar Mesons from Lattice QCD and Implications on the Nature of the D_{s0}^*(2317)

We study the scattering of light pseudoscalar mesons ($π$, $K$) off charmed mesons ($D$, $D_s$) in full lattice QCD. The S-wave scattering lengths are calculated using Lüscher's finite volume technique. We use a relativistic formulation for the charm quark. For the light quark, we use domain-wall fermions in the valence sector and improved Kogut-Susskind sea quarks. We calculate the scattering lengths of isospin-3/2 $Dπ$, $D_sπ$, $D_sK$, isospin-0 $D\bar{K}$ and isospin-1 $D\bar{K}$ channels on the lattice. For the chiral extrapolation, we use a chiral unitary approach to next-to-leading order, which at the same time allows us to give predictions for other channels. It turns out that our results support the interpretation of the $D_{s0}^*(2317)$ as a $DK$ molecule. At the same time, we also update a prediction for the isospin breaking hadronic decay width $Γ(D_{s0}^*(2317)\to D_sπ)$ to $(133\pm22)$ keV.

hep-lat↗

arXiv2018

Quasi-Parton Distribution Function in Lattice Perturbation Theory

Large momentum effective field theory provides a new direction for lattice QCD calculations of hadronic structure functions, such as parton distribution functions (PDFs), meson distribution amplitudes, and so on, directly with $x$-dependence. In the framework of Lattice Perturbation Theory (LPT), we compute the one-loop quark-in-quark quasi-PDF with the naïve fermion action ($\tilde{q}^{\mathrm{nv}}$) and quasi-PDF with Wilson-Clover action ($\tilde{q}^{\mathrm{WC}}$) and show that $\tilde{q}^{\mathrm{nv}}$ reduces to the continuum quasi-PDF in the continuum limit. We point out, however, that the continuum limit and massless quark limit do not commute. We find that the condition to recover the same collinear divergence that the quasi-PDF has in continuum QCD is $aP_3^2\approx m$ and $m\ll P_3$, while the condition to fully recover the continuum quasi-PDF is $aP_{3}^{2}\ll m\ll P_{3}$, where $P_3$ is the momentum in the direction of the quark's motion (longitudinal direction). These two conditions are based on perturbation calculations and should not be applied to non-perturbative calculations because the non-perturbative effects cure the collinear divergence. The correction to the quasi-PDF using the naïve fermion action is due to the Wilson term and can be viewed as an $\mathcal{O}\left(a^{1}\right)$ correction. For nonzero $r$, the $\mathcal{O}\left(a^{1}\right)$ corrections are subsequently mixed with the quasi-PDF using the naïve fermion action.

hep-ph↗

arXiv2018

Lattice Improvement in Lattice Effective Field Theory

Lattice calculations using the framework of effective field theory have been applied to a wide range few-body and many-body systems. One of the challenges of these calculations is to remove systematic errors arising from the nonzero lattice spacing. Fortunately, the lattice improvement program pioneered by Symanzik provides a formalism for doing this. While lattice improvement has already been utilized in lattice effective field theory calculations, the effectiveness of the improvement program has not been systematically benchmarked. In this work we use lattice improvement to remove lattice errors for a one-dimensional system of bosons with zero-range interactions. We construct the improved lattice action up to next-to-next-to-leading order and verify that the remaining errors scale as the fourth power of the lattice spacing for observables involving as many as five particles. Our results provide a guide for increasing the accuracy of future calculations in lattice effective field theory with improved lattice actions.

hep-lat↗

arXiv2018

Three-particle bound states in a finite volume: unequal masses and higher partial waves

An explicit expression for the finite-volume energy shift of shallow three-body bound states for non-identical particles is obtained in the unitary limit. The inclusion of the higher partial waves is considered. To this end, the method of arXiv:1412.4969 (Meißner et al.) is generalized for the case of unequal masses and arbitrary angular momenta. It is shown that in the S-wave and in the equal mass limit, the result from arXiv:1412.4969 is reproduced.

hep-lat↗

arXiv2018

A new method to study the number of colors in the final-state interactions of hadrons

We match the $ππ\toππ$ scattering amplitudes of Chiral Perturbation Theory with those from dispersion relations that respect analyticity and coupled channel unitarity, as well as accurately describing experiment. Their dependence on the number of colors ($N_C$) is obtained. By varying $N_C$ the trajectories of the poles and residues (the couplings to $ππ$) of light mesons, the $σ$, $f_0(980)$, $ρ(770)$ and $f_2(1270)$ are investigated. Our results show that the method proposed is a reliable way to study the $N_C$ dependence in hadron-hadron scattering with final-state interactions.

hep-ph↗

arXiv2018

Behavior of the collective rotor in wobbling motion

The behavior of the collective rotor in wobbling motion is investigated within the particle-rotor model for the nucleus $^{135}$Pr by transforming the wave functions from the $K$-representation to the $R$-representation. After reproducing the experimental energy spectra and wobbling frequencies, the evolution of the wobbling mode in $^{135}$Pr, from transverse at low spins to longitudinal at high spins, is illustrated by the distributions of the total angular momentum in the intrinsic reference frame (azimuthal plot). Finally, the coupling schemes of the angular momenta of the rotor and the high-$j$ particle for transverse and longitudinal wobbling are obtained from the analysis of the probability distributions of the rotor angular momentum ($R$-plots) and their projections onto the three principal axes ($K_R$-plots).

nucl-th↗

arXiv2018

$J/ψ\to γη'π^+π^-$ and the structure observed around the $\bar pp$ threshold

We analyze the origin of the structure observed in the reaction $J/ψ\to γη'π^+π^-$ for $η'π^+π^-$ invariant masses close to the antiproton-proton ($\bar pp$) threshold, commonly associated with the $X(1835)$ resonance. Specifically, we explore the effect of a possible contribution from the two-step process $J/ψ\to γ\bar NN \to γη'π^+π^-$. The calculation is performed in distorted-wave Born approximation which allows an appropriate inclusion of the $\bar NN$ interaction in the transition amplitude. The $\bar NN$ amplitude itself is generated from a corresponding potential recently derived within chiral effective field theory. We are able to reproduce the measured spectra for the reactions $J/ψ\to γ\bar pp$ and $J/ψ\to γη'π^+π^-$ for invariant masses around the $\bar pp$ threshold. The structure seen in the $η'π^+π^-$ spectrum emerges as a threshold effect due to the opening of the $\bar pp$ channel.

hep-ph↗

arXiv2018

Microscopic Clustering in Light Nuclei

We review recent experimental and theoretical progress in understanding the microscopic details of clustering in light nuclei. We discuss recent experimental results on $α$-conjugate systems, molecular structures in neutron-rich nuclei, and constraints for ab initio theory. We then examine nuclear clustering in a wide range of theoretical methods, including the resonating group and generator coordinate methods, antisymmetrized molecular dynamics, Tohsaki-Horiuchi-Schuck-Röpke wave function and container model, no-core shell model methods, continuum quantum Monte Carlo, and lattice effective field theory.

nucl-th↗

arXiv2018

Once more on the Higgs decay into two photons

We comment on the recently reiterated claim that the contribution of the W-boson loop to the Higgs boson decay into two photons leads to different expressions in the $R_ξ$ gauge and the unitary gauge. By applying a gauge-symmetry preserving regularization with higher-order covariant derivatives we reproduce once again the "classical" gauge-independent result.

hep-ph↗

arXiv2018

Derivation of spontaneously broken gauge symmetry from the consistency of effective field theory I: Massive vector bosons coupled to a scalar field

We revisit the problem of deriving local gauge invariance with spontaneous symmetry breaking in the context of an effective field theory. Previous derivations were based on the condition of tree-order unitarity. However, the modern point of view considers the Standard Model as the leading order approximation to an effective field theory. As tree-order unitarity is in any case violated by higher-order terms in an effective field theory, it is instructive to investigate a formalism which can be also applied to analyze higher-order interactions. In the current work we consider an effective field theory of massive vector bosons interacting with a massive scalar field. We impose the conditions of generating the right number of constraints for systems with spin-one particles and perturbative renormalizability as well as the separation of scales at one-loop order. We find that the above conditions impose severe restrictions on the coupling constants of the interaction terms. Except for the strengths of the self-interactions of the scalar field, that can not be determined at this order from the analysis of three- and four-point functions, we recover the gauge-invariant Lagrangian with spontaneous symmetry breaking taken in the unitary gauge as the leading order approximation to an effective field theory. We also outline the additional work that is required to finish this program.

hep-th↗

arXiv2018

Effective field theory for collective rotations and vibrations of triaxially deformed nuclei

The effective field theory (EFT) for triaxially deformed even-even nuclei is generalized to include the vibrational degrees of freedom. The pertinent Hamiltonian is constructed up to next-to-leading order. The leading order part describes the vibrational motion, and the NLO part couples rotations to vibrations. The applicability of the EFT Hamiltonian is examined through the description of the energy spectra of the ground state bands, $γ$-bands, and $K=4$ bands in the $^{108, 110, 112}$Ru isotopes. It is found that by taking into account the vibrational degrees of freedom, the deviations for high-spin states in the $γ$-band observed in the EFT with only rotational degrees of freedom disappear. This supports the importance of including vibrational degrees of freedom in the EFT formulation for the collective motion of triaxially deformed nuclei.

nucl-th↗

arXiv2018

The Tjon Band in Nuclear Lattice Effective Field Theory

We explore the lattice spacing dependence in Nuclear Lattice Effective Field Theory for few-body systems up to next-to-next-to leading order in chiral effective field theory including all isospin breaking and electromagnetic effects, the complete two-pion-exchange potential and the three-nucleon forces. We calculate phase shifts in the neutron-proton system and proton-proton systems as well as the scattering length in the neutron-neutron system. We then perform a full next-to-next-to-leading order calculation with two-nucleon and three-nucleon forces for the triton and helium-4 and analyse their binding energy correlation. We show how the Tjon band is reached by decreasing the lattice spacing and confirm the continuum observation that a four-body force is not necessary to describe light nuclei.

nucl-th↗