@article{yu_yapa_konig_2024, title={Complex scaling in finite volume}, volume={109}, ISSN={["2469-9993"]}, url={https://doi.org/10.1103/PhysRevC.109.014316}, DOI={10.1103/PhysRevC.109.014316}, abstractNote={Quantum resonances, i.e., metastable states with a finite lifetime, play an important role in nuclear physics and other domains. Describing this phenomenon theoretically is generally a challenging task. In this work, we combine two established techniques to address this challenge. Complex scaling makes it possible to calculate resonances with bound-state-like methods. Finite-volume simulations exploit the fact that the infinite-volume properties of quantum systems are encoded in how discrete energy levels change as one varies the size of the volume. We apply complex scaling to systems in finite periodic boxes and derive the volume dependence of states in this scenario, demonstrating with explicit examples how one can use these relations to infer infinite-volume resonance energies and lifetimes.}, number={1}, journal={PHYSICAL REVIEW C}, author={Yu, Hang and Yapa, Nuwan and Konig, Sebastian}, year={2024}, month={Jan} }
 @article{taurence_konig_2024, title={Radius extrapolations for two-body bound states in finite volume}, volume={109}, ISSN={["2469-9993"]}, url={https://doi.org/10.1103/PhysRevC.109.054315}, DOI={10.1103/PhysRevC.109.054315}, abstractNote={Simulations of quantum systems in finite volume have proven to be a useful tool for calculating physical observables. Such studies to date have focused primarily on understanding the volume dependence of binding energies, from which it is possible to extract asymptotic properties of the corresponding bound state, as well as on extracting scattering information. For bound states, all properties depend on the size of the finite volume, and for precision studies it is important to understand such effects. In this work, we therefore derive the volume dependence of the mean squared radius of a two-body bound state, using a technique that can be generalized to other static properties in the future. We test our results with explicit numerical examples and demonstrate that we can robustly extract infinite-volume radii from finite-volume simulations in cubic boxes with periodic boundary conditions.}, number={5}, journal={PHYSICAL REVIEW C}, author={Taurence, Anderson and Konig, Sebastian}, year={2024}, month={May} }
 @article{yu_koenig_lee_2023, title={Charged-Particle Bound States in Periodic Boxes}, volume={131}, ISSN={["1079-7114"]}, url={https://doi.org/10.1103/PhysRevLett.131.212502}, DOI={10.1103/PhysRevLett.131.212502}, abstractNote={We consider the binding energy of a two-body system with a repulsive Coulomb interaction in a finite periodic volume. We define the finite-volume Coulomb potential as the usual Coulomb potential, except that the distance is defined as the shortest separation between the two bodies in the periodic volume. We investigate this problem in one and three-dimensional periodic boxes and derive the asymptotic behavior of the volume dependence for bound states with zero angular momentum in terms of Whittaker functions. We benchmark our results against numerical calculations and show how the method can be used to extract asymptotic normalization coefficients for charged-particle bound states. The results we derive here have immediate applications for calculations of atomic nuclei in finite periodic volumes for the case where the leading finite-volume correction is associated with two charged clusters.}, number={21}, journal={PHYSICAL REVIEW LETTERS}, author={Yu, Hang and Koenig, Sebastian and Lee, Dean}, year={2023}, month={Nov} }
 @article{konig_2023, title={Efficient few-body calculations in finite volume}, volume={2453}, ISBN={["*****************"]}, ISSN={["1742-6596"]}, DOI={10.1088/1742-6596/2453/1/012025}, abstractNote={Abstract}, journal={13TH INTERNATIONAL SPRING SEMINAR ON NUCLEAR PHYSICS PERSPECTIVES AND CHALLENGES IN NUCLEAR STRUCTURE AFTER 70 YEARS OF SHELL MODEL, ISS 2022}, author={Konig, S.}, year={2023} }
 @article{yapa_fossez_könig_2023, title={Eigenvector continuation for emulating and extrapolating two-body resonances}, url={https://doi.org/10.1103/PhysRevC.107.064316}, DOI={10.1103/PhysRevC.107.064316}, abstractNote={The study of open quantum systems (OQSs), i.e., systems interacting with an environment, impacts our understanding of exotic nuclei in low-energy nuclear physics, hadrons, cold-atom systems, or even noisy intermediate-scale quantum computers. Such systems often exhibit resonance states characterized by energy positions and dispersions (or decay widths), the properties of which can be difficult to predict theoretically due to their coupling to the continuum of scattering states. Dealing with this phenomenon poses challenges both conceptually and numerically. For that reason, we investigate how the reduced basis method known as eigenvector continuation (EC), which has emerged as a powerful tool to emulate bound and scattering states in closed quantum systems, can be used to study resonance properties. In particular, we present a generalization of EC that we call conjugate-augmented eigenvector continuation, which is based on the complex-scaling method and designed to predict Gamow-Siegert states, and thus resonant properties of OQSs, using only bound-state wave functions as input.}, journal={Physical Review C}, author={Yapa, Nuwan and Fossez, Kévin and König, Sebastian}, year={2023}, month={Jun} }
 @article{seutin_hernandez_miyagi_bacca_hebeler_koenig_schwenk_2023, title={Magnetic dipole operator from chiral effective field theory for many-body expansion methods}, volume={108}, ISSN={["2469-9993"]}, DOI={10.1103/PhysRevC.108.054005}, abstractNote={Many-body approaches for atomic nuclei generally rely on a basis expansion of the nuclear states, interactions, and current operators. In this work, we derive the representation of the magnetic dipole operator in plane-wave and harmonic-oscillator basis states, as needed for Faddeev calculations of few-body systems or many-body calculations within, e.g., the no-core shell model, the in-medium renormalization group, coupled-cluster theory, or the nuclear shell model. We focus in particular on the next-to-leading-order two-body contributions derived from chiral effective field theory. We provide detailed benchmarks and also comparisons with quantum Monte Carlo results for three-body systems. The derived operator matrix elements represent the basic input for studying magnetic properties of atomic nuclei based on chiral effective field theory.}, number={5}, journal={PHYSICAL REVIEW C}, author={Seutin, R. and Hernandez, O. J. and Miyagi, T. and Bacca, S. and Hebeler, K. and Koenig, S. and Schwenk, A.}, year={2023}, month={Nov} }
 @article{bazin_becker_bonaiti_elster_fossez_frederico_gnech_hebborn_higgins_hlophe_et al._2023, title={Perspectives on Few-Body Cluster Structures in Exotic Nuclei}, volume={64}, ISSN={["1432-5411"]}, url={http://dx.doi.org/10.1007/s00601-023-01794-0}, DOI={10.1007/s00601-023-01794-0}, abstractNote={It is a fascinating phenomenon in nuclear physics that states with a pronounced few-body structure can emerge from the complex dynamics of many nucleons. Such halo or cluster states often appear near the boundaries of nuclear stability. As such, they are an important part of the experimental program beginning at the Facility for Rare Isotope Beams (FRIB). A concerted effort of theory and experiment is necessary both to analyze experiments involving effective few-body states, as well as to constrain and refine theories of the nuclear force in light of new data from these experiments. As a contribution to exactly this effort, this paper compiles a collection of ``perspectives'' that emerged out of the Topical Program ``Few-body cluster structures in exotic nuclei and their role in FRIB experiments'' that was held at FRIB in August 2022 and brought together theorists and experimentalists working on this topic.}, number={2}, journal={FEW-BODY SYSTEMS}, author={Bazin, Daniel and Becker, Kevin and Bonaiti, Francesca and Elster, Charlotte and Fossez, Kevin and Frederico, Tobias and Gnech, Alex and Hebborn, Chloe and Higgins, Michael and Hlophe, Linda and et al.}, year={2023}, month={May} }
 @article{viviani_konig_kievsky_marcucci_singh_doce_2023, title={Role of three-body dynamics in nucleon-deuteron correlation functions}, volume={108}, ISSN={["2469-9993"]}, url={https://doi.org/10.1103/PhysRevC.108.064002}, DOI={10.1103/PhysRevC.108.064002}, abstractNote={Correlation functions of hadrons can be accessed in high-energy collisions of atomic nuclei, revealing information about the underlying interaction. This work complements experimental efforts to study nucleon-deuteron $Nd$ -- with $N=p$ (proton) or $N=n$ (neutron) -- correlations with theory evaluations using different techniques. The correlation functions $C_{nd}$ and $C_{pd}$ are calculated based on scattering wave function, extending previous benchmarks for the $Nd$ scattering matrix to this new observable. We use hyperspherical harmonics and Faddeev techniques with one of the widely used nucleon-nucleon ($NN$) interactions, the Argonne $v_{18}$ potential. Moreover, in the low-energy region we perform additional calculations in the framework of pionless effective field theory. The $pd$ correlation function is computed in the large-energy region to make contact with a recent measurement by the ALICE Collaboration. We show that the scattering wave function has the proper dynamical input to describe an initial rise and subsequent oscillations of $C_{pd}$ as a function of the energy. Effects on the observables using different $NN$ and three-nucleon potentials are evaluated with the conclusion that variations of around $2\%$ are observed. Although these effects are small, future measurements can go beyond this accuracy allowing for new detailed studies of strong interaction in light nuclear systems. The present study supports the current efforts devoted to the measurement of correlation functions in systems dominated by the strong interactions, such as $pd$, $ppp$, $\Lambda d$ and $pp\Lambda$.}, number={6}, journal={PHYSICAL REVIEW C}, author={Viviani, M. and Konig, S. and Kievsky, A. and Marcucci, L. E. and Singh, B. and Doce, O. Vazquez}, year={2023}, month={Dec} }
 @article{peng_lyu_konig_long_2022, title={Constructing chiral effective field theory around unnatural leading-order interactions}, volume={105}, ISSN={["2469-9993"]}, url={http://dx.doi.org/10.1103/physrevc.105.054002}, DOI={10.1103/physrevc.105.054002}, abstractNote={A momentum-dependent formulation based on a stationary spin-0 and isospin-1 dibaryon field is proposed to improve convergence of chiral effective field theory in the 1 S 0 channel of NN scattering. Although the two-parameter leading-order interaction appears to be unnatural, it nevertheless has the necessary features of an effective field theory. A rapid order-by-order convergence is found in 1 S 0 . As an application beyond the two-body level, the triton binding energy is studied and compared to standard chiral effective field theory with partly perturbative pions. The consistency of the chiral Lagrangian for the new formulation is examined by working out the pionic radiative corrections, and consequences of nontrivial chiral-connection terms are discussed.}, number={5}, journal={PHYSICAL REVIEW C}, author={Peng, Rui and Lyu, Songlin and Konig, Sebastian and Long, Bingwei}, year={2022}, month={May} }
 @article{tews_davoudi_ekstrom_holt_becker_briceno_dean_detmold_drischler_duguet_et al._2022, title={Nuclear Forces for Precision Nuclear Physics: A Collection of Perspectives}, volume={63}, ISSN={["1432-5411"]}, url={http://dx.doi.org/10.1007/s00601-022-01749-x}, DOI={10.1007/s00601-022-01749-x}, abstractNote={This is a collection of perspective pieces contributed by the participants of the Institute for Nuclear Theory’s Program on Nuclear Physics for Precision Nuclear Physics which was held virtually from April 19 to May 7, 2021. The collection represents the reflections of a vibrant and engaged community of researchers on the status of theoretical research in low-energy nuclear physics, the challenges ahead, and new ideas and strategies to make progress in nuclear structure and reaction physics, effective field theory, lattice QCD, quantum information, and quantum computing. The contributed pieces solely reflect the perspectives of the respective authors and do not represent the viewpoints of the Institute for Nuclear theory or the organizers of the program.}, number={4}, journal={FEW-BODY SYSTEMS}, author={Tews, Ingo and Davoudi, Zohreh and Ekstrom, Andreas and Holt, Jason D. and Becker, Kevin and Briceno, Raul and Dean, David J. and Detmold, William and Drischler, Christian and Duguet, Thomas and et al.}, year={2022}, month={Dec} }
 @article{dietz_hammer_konig_schwenk_2022, title={Three-body resonances in pionless effective field theory}, volume={105}, ISSN={["2469-9993"]}, url={https://doi.org/10.1103/PhysRevC.105.064002}, DOI={10.1103/PhysRevC.105.064002}, abstractNote={We investigate the appearance of resonances in three-body systems using pionless effective field theory at leading order with two complementary methods. The Faddeev equation is analytically continued to the unphysical sheet adjacent to the positive real energy axis using a contour rotation. We consider both the three-boson system and the three-neutron system. For the former, we calculate the trajectory of Borromean three-body Efimov states turning into resonances as they cross the three-body threshold. For the latter, we find no sign of three-body resonances or virtual states at leading order. This result is validated by exploring the level structure of three-body states in a finite volume approach.}, number={6}, journal={PHYSICAL REVIEW C}, author={Dietz, S. and Hammer, H-W and Konig, S. and Schwenk, A.}, year={2022}, month={Jun} }
 @article{yapa_konig_2022, title={Volume extrapolation via eigenvector continuation}, volume={106}, ISSN={["2469-9993"]}, url={https://doi.org/10.1103/PhysRevC.106.014309}, DOI={10.1103/PhysRevC.106.014309}, abstractNote={We develop an extension of eigenvector continuation (EC) that makes it possible to extrapolate simulations of quantum systems in finite periodic boxes across large ranges of box sizes. The formal justification for this approach, which we call finite-volume eigenvector continuation (FVEC), is provided by matching periodic functions at different box sizes. As concrete FVEC implementation we use a discrete variable representation based on plane-wave states and present several applications calculated within this framework.}, number={1}, journal={PHYSICAL REVIEW C}, author={Yapa, Nuwan and Konig, Sebastian}, year={2022}, month={Jul} }
 @article{friman-gayer_romig_huether_albe_bacca_beck_berger_birkhan_hebeler_hernandez_et al._2021, title={Role of Chiral Two-Body Currents in Li-6 Magnetic Properties in Light of a New Precision Measurement with the Relative Self-Absorption Technique}, volume={126}, ISSN={["1079-7114"]}, url={http://dx.doi.org/10.1103/physrevlett.126.102501}, DOI={10.1103/physrevlett.126.102501}, abstractNote={A direct measurement of the decay width of the excited 0_{1}^{+} state of ^{6}Li using the relative self-absorption technique is reported. Our value of Γ_{γ,0_{1}^{+}→1_{1}^{+}}=8.17(14)_{stat.}(11)_{syst.}  eV provides sufficiently low experimental uncertainties to test modern theories of nuclear forces. The corresponding transition rate is compared to the results of ab initio calculations based on chiral effective field theory that take into account contributions to the magnetic dipole operator beyond leading order. This enables a precision test of the impact of two-body currents that enter at next-to-leading order.}, number={10}, journal={PHYSICAL REVIEW LETTERS}, publisher={American Physical Society (APS)}, author={Friman-Gayer, U. and Romig, C. and Huether, T. and Albe, K. and Bacca, S. and Beck, T. and Berger, M. and Birkhan, J. and Hebeler, K. and Hernandez, J. and et al.}, year={2021}, month={Mar} }
 @article{könig_ekström_hebeler_lee_schwenk_2020, title={Eigenvector continuation as an efficient and accurate emulator for uncertainty quantification}, volume={810}, url={https://doi.org/10.1016/j.physletb.2020.135814}, DOI={10.1016/j.physletb.2020.135814}, abstractNote={First principles calculations of atomic nuclei based on microscopic nuclear forces derived from chiral effective field theory (EFT) have blossomed in the past years. A key element of such ab initio studies is the understanding and quantification of systematic and statistical errors arising from the omission of higher-order terms in the chiral expansion as well as the model calibration. While there has been significant progress in analyzing theoretical uncertainties for nucleon-nucleon scattering observables, the generalization to multi-nucleon systems has not been feasible yet due to the high computational cost of evaluating observables for a large set of low-energy couplings. In this Letter we show that a new method called eigenvector continuation (EC) can be used for constructing an efficient and accurate emulator for nuclear many-body observables, thereby enabling uncertainty quantification in multi-nucleon systems. We demonstrate the power of EC emulation with a proof-of-principle calculation that lays out all correlations between bulk ground-state observables in the few-nucleon sector. On the basis of ab initio calculations for the ground-state energy and radius in 4He, we demonstrate that EC is more accurate and efficient compared to established methods like Gaussian processes.}, journal={Physics Letters B}, publisher={Elsevier BV}, author={König, S. and Ekström, A. and Hebeler, K. and Lee, D. and Schwenk, A.}, year={2020}, month={Nov}, pages={135814} }
 @article{koenig_2020, title={Energies and radii of light nuclei around unitarity}, volume={56}, ISSN={["1434-601X"]}, url={http://dx.doi.org/10.1140/epja/s10050-020-00098-9}, DOI={10.1140/epja/s10050-020-00098-9}, abstractNote={Abstract}, number={4}, journal={EUROPEAN PHYSICAL JOURNAL A}, author={Koenig, Sebastian}, year={2020}, month={Apr} }
 @misc{koenig_2020, title={Few-Body Bound States and Resonances in Finite Volume}, volume={61}, ISSN={["1432-5411"]}, url={https://doi.org/10.1007/s00601-020-01550-8}, DOI={10.1007/s00601-020-01550-8}, abstractNote={Abstract}, number={3}, journal={FEW-BODY SYSTEMS}, publisher={Springer Science and Business Media LLC}, author={Koenig, Sebastian}, year={2020}, month={Jun} }
 @article{demol_duguet_ekstrom_frosini_hebeler_koenig_lee_schwenk_soma_tichai_2020, title={Improved many-body expansions from eigenvector continuation}, volume={101}, ISSN={["2469-9993"]}, url={https://doi.org/10.1103/PhysRevC.101.041302}, DOI={10.1103/PhysRevC.101.041302}, abstractNote={Quantum many-body theory has witnessed tremendous progress in various fields, ranging from atomic and solid-state physics to quantum chemistry and nuclear structure. Due to the inherent computational burden linked to the ab initio treatment of microscopic fermionic systems, it is desirable to obtain accurate results through low-order perturbation theory. In atomic nuclei however, effects such as strong short-range repulsion between nucleons can spoil the convergence of the expansion and make the reliability of perturbation theory unclear. Mathematicians have devised an extensive machinery to overcome the problem of divergent expansions by making use of so-called resummation methods. In large-scale many-body applications such schemes are often of limited use since no a priori analytical knowledge of the expansion is available. We present here eigenvector continuation as an alternative resummation tool that is both efficient and reliable because it is based on robust and simple mathematical principles.}, number={4}, journal={PHYSICAL REVIEW C}, publisher={American Physical Society (APS)}, author={Demol, P. and Duguet, T. and Ekstrom, A. and Frosini, M. and Hebeler, K. and Koenig, S. and Lee, D. and Schwenk, A. and Soma, V and Tichai, A.}, year={2020}, month={Apr} }
 @misc{hammer_koenig_kolck_2020, title={Nuclear effective field theory: Status and perspectives}, volume={92}, ISSN={["1539-0756"]}, url={https://doi.org/10.1103/RevModPhys.92.025004}, DOI={10.1103/RevModPhys.92.025004}, abstractNote={The nuclear physics landscape has been redesigned as a sequence of effective field theories (EFTs) connected to the Standard Model through symmetries and lattice simulations of Quantum Chromodynamics (QCD). EFTs in this sequence are expansions around different low-energy limits of QCD, each with its own characteristics, scales, and ranges of applicability regarding energy and number of nucleons. We review each of the three main nuclear EFTs---Chiral, Pionless, Halo/Cluster---highlighting their similarities, differences, and connections. In doing so, we survey the structural properties and reactions of nuclei that have been derived from the ab initio solution of the few- and many-body problem built upon EFT input.}, number={2}, journal={REVIEWS OF MODERN PHYSICS}, publisher={American Physical Society (APS)}, author={Hammer, H. -W. and Koenig, Sebastian and Kolck, U.}, year={2020}, month={Jun} }
 @inbook{könig_2020, title={The Unitarity Expansion for Light Nuclei}, url={http://dx.doi.org/10.1007/978-3-030-32357-8_54}, DOI={10.1007/978-3-030-32357-8_54}, abstractNote={It is argued here that (at least light) nuclei may reside in a sweet spot: bound weakly enough to be insensitive to the details of the interaction, but dense enough to be insensitive to the exact values of the large two-body scattering lengths as well. In this scenario a systematic expansion of nuclear observables around the unitarity limit converges. In particular, the nuclear force in this scheme is constructed such that the gross features of states in the nuclear chart are determined by a very simple leading-order interaction, whereas—much like the fine structure of atomic spectra—observables are moved to their physical values by small perturbative corrections. Explicit evidence in favor of this conjecture is shown for the binding energies of three and four nucleons.}, booktitle={Recent Progress in Few-Body Physics}, publisher={Springer International Publishing}, author={König, Sebastian}, year={2020}, pages={311–320} }
 @article{four-body scale in universal few-boson systems_2019, url={http://dx.doi.org/10.1103/physrevlett.122.143001}, DOI={10.1103/physrevlett.122.143001}, abstractNote={The role of an intrinsic four-body scale in universal few-boson systems is the subject of active debate. We study these systems within the framework of effective field theory. For systems of up to six bosons we establish that no four-body scale appears at leading order (LO). However, we find that at next-to-leading order (NLO) a four-body force is needed to obtain renormalized results for binding energies. With the associated parameter fixed to the binding energy of the four-boson system, this force is shown to renormalize the five- and six-body systems as well. We present an original ansatz for the short-distance limit of the bosonic A-body wave function from which we conjecture that new A-body scales appear at N^{A-3} LO. As a specific example, calculations are presented for clusters of helium atoms. Our results apply more generally to other few-body systems governed by a large scattering length, such as light nuclei and halo states, the low-energy properties of which are independent of the detailed internal structure of the constituents.}, journal={Physical Review Letters}, year={2019}, month={Apr} }
 @article{from bound states to the continuum_2019, DOI={10.1088/1361-6471/abb129}, abstractNote={Abstract}, journal={J. Phys. G: Nucl. Part. Phys. 47 123001 (2020)}, year={2019}, month={Dec} }
 @article{signatures of few-body resonances in finite volume_2018, url={http://dx.doi.org/10.1103/physrevc.98.034004}, DOI={10.1103/PhysRevC.98.034004}, abstractNote={We study systems of bosons and fermions in finite periodic boxes and show how the existence and properties of few-body resonances can be extracted from studying the volume dependence of the calculated energy spectra. Using a plane-wave-based discrete variable representation to conveniently implement periodic boundary conditions, we establish that avoided level crossings occur in the spectra of up to four particles and can be linked to the existence of multi-body resonances. To benchmark our method we use two-body calculations, where resonance properties can be determined with other methods, as well as a three-boson model interaction known to generate a three-boson resonance state. Finding good agreement for these cases, we then predict three-body and four-body resonances for models using a shifted Gaussian potential. Our results establish few-body finite-volume calculations as a new tool to study few-body resonances. In particular, the approach can be used to study few-neutron systems, where such states have been conjectured to exist.}, journal={Physical Review C}, year={2018}, month={Sep} }
 @article{koenig_lee_2018, title={Volume dependence of N-body bound states}, volume={779}, ISSN={["1873-2445"]}, DOI={10.1016/j.physletb.2018.01.060}, abstractNote={We derive the finite-volume correction to the binding energy of an N-particle quantum bound state in a cubic periodic volume. Our results are applicable to bound states with arbitrary composition and total angular momentum, and in any number of spatial dimensions. The only assumptions are that the interactions have finite range. The finite-volume correction is a sum of contributions from all possible breakup channels. In the case where the separation is into two bound clusters, our result gives the leading volume dependence up to exponentially small corrections. If the separation is into three or more clusters, there is a power-law factor that is beyond the scope of this work, however our result again determines the leading exponential dependence. We also present two independent methods that use finite-volume data to determine asymptotic normalization coefficients. The coefficients are useful to determine low-energy capture reactions into weakly bound states relevant for nuclear astrophysics. Using the techniques introduced here, one can even extract the infinite-volume energy limit using data from a single-volume calculation. The derived relations are tested using several exactly solvable systems and numerical examples. We anticipate immediate applications to lattice calculations of hadronic, nuclear, and cold atomic systems.}, journal={PHYSICS LETTERS B}, publisher={Elsevier BV}, author={Koenig, Sebastian and Lee, Dean}, year={2018}, month={Apr}, pages={9–15} }
 @article{hammer_könig_2017, title={General Aspects of Effective Field Theories and Few-Body Applications}, url={http://dx.doi.org/10.1007/978-3-319-53336-0_4}, DOI={10.1007/978-3-319-53336-0_4}, abstractNote={Effective field theory provides a powerful framework to exploit a separation of scales in physical systems. In these lectures, we discuss some general aspects of effective field theories and their application to few-body physics. In particular, we consider an effective field theory for non-relativistic particles with resonant short-range interactions where certain parts of the interaction need to be treated nonperturbatively. As an application, we discuss the so-called pionless effective field theory for low-energy nuclear physics. The extension to include long-range interactions mediated by photon and pion-exchange is also addressed.}, journal={An Advanced Course in Computational Nuclear Physics}, publisher={Springer International Publishing}, author={Hammer, Hans-Werner and König, Sebastian}, year={2017}, pages={93–153} }
 @article{könig_grießhammer_hammer_kolck_2017, title={Nuclear Physics Around the Unitarity Limit}, volume={118}, url={http://dx.doi.org/10.1103/physrevlett.118.202501}, DOI={10.1103/physrevlett.118.202501}, abstractNote={We argue that many features of the structure of nuclei emerge from a strictly perturbative expansion around the unitarity limit, where the two-nucleon S waves have bound states at zero energy. In this limit, the gross features of states in the nuclear chart are correlated to only one dimensionful parameter, which is related to the breaking of scale invariance to a discrete scaling symmetry and set by the triton binding energy. Observables are moved to their physical values by small perturbative corrections, much like in descriptions of the fine structure of atomic spectra. We provide evidence in favor of the conjecture that light, and possibly heavier, nuclei are bound weakly enough to be insensitive to the details of the interactions but strongly enough to be insensitive to the exact size of the two-nucleon system.}, number={20}, journal={Physical Review Letters}, publisher={American Physical Society (APS)}, author={König, Sebastian and Grießhammer, Harald W. and Hammer, H.-W. and Kolck, U.}, year={2017}, month={May} }
 @article{second-order perturbation theory for 3he and pd scattering in pionless eft_2017, url={http://dx.doi.org/10.1088/1361-6471/aa60d6}, DOI={10.1088/1361-6471/aa60d6}, abstractNote={This work implements pionless effective field theory with the two-nucleon system expanded around the unitarity limit at second order perturbation theory. The expansion is found to converge well. All Coulomb effects are treated in perturbation theory, including two-photon contributions at next-to-next-to-leading order. After fixing a three-nucleon force to the 3He binding energy at this order, proton-deuteron scattering in the doublet S-wave channel is calculated for moderate center-of-mass momenta.}, journal={Journal of Physics G: Nuclear and Particle Physics}, year={2017}, month={Jun} }
 @article{effective theory of 3h and 3he_2016, url={http://dx.doi.org/10.1088/0954-3899/43/5/055106}, DOI={10.1088/0954-3899/43/5/055106}, abstractNote={We present a new perturbative expansion for pionless effective field theory with Coulomb interactions in which at leading order the spin-singlet nucleon-nucleon channels are taken in the unitarity limit. Presenting results up to next-to-leading order for the Phillips line and the neutron-deuteron doublet-channel phase shift, we find that a perturbative expansion in the inverse 1S0 scattering lengths converges rapidly. Using a new systematic treatment of the proton-proton sector that isolates the divergence due to one-photon exchange, we renormalize the corresponding contribution to the 3H-3He binding energy splitting and demonstrate that the Coulomb force in pionless EFT is a completely perturbative effect in the trinucleon bound-state regime. In our new expansion, the leading order is exactly isospin-symmetric. At next-to-leading order, we include isospin breaking via the Coulomb force and two-body scattering lengths, and find for the energy splitting (E_B(3He)-E_B(3H))^NLO = (-0.86 +/- 0.17) MeV.}, journal={Journal of Physics G: Nuclear and Particle Physics}, year={2016}, month={Jun} }
 @article{könig_hammer_2016, title={The proton–deuteron scattering length in pionless EFT}, volume={113}, DOI={10.1051/epjconf/201611304011}, abstractNote={We present a fully perturbative calculation of the quartet-channel proton–deuteron scattering length (4 a p –d ) up to next-to-next-to-leading order (NNLO) in pionless effective field theory. In particular, we use a framework that consistently extracts the Coulomb-modified effective range function for a screened Coulomb potential in momentum space. We find a natural convergence pattern as we go to higher orders in the EFT expansion. Our NNLO result of (10.9 ± 0.4) fm agrees with older experimental determinations but deviates from more recent calculations, which find values around 14 fm. To resolve this discrepancy, we discuss the scheme dependence of Coulomb subtractions in a three-body system.}, journal={EPJ Web of Conferences}, publisher={EDP Sciences}, author={König, Sebastian and Hammer, Hans-Werner}, editor={Elster, C. and Phillips, D.R. and Roberts, C.D.Editors}, year={2016}, pages={04011} }
 @article{more_könig_furnstahl_hebeler_2015, title={Deuteron electrodisintegration with unitarily evolved potentials}, volume={92}, DOI={10.1103/physrevc.92.064002}, abstractNote={Renormalization group (RG) methods used to soften Hamiltonians for nuclear many-body calculations change the effective resolution of the interaction. For nucleon knock-out processes, these RG transformations leave cross sections invariant, but initial-state wave functions, interaction currents, and final-state interactions are individually altered. This has implications for the factorization of nuclear structure and reactions. We use deuteron electrodisintegration as a controlled laboratory for studying how structure and reaction components are modified under RG evolution, without the complication of three-body forces or currents. The dependence of these changes on kinematics is explored.}, number={6}, journal={Physical Review C}, publisher={American Physical Society (APS)}, author={More, S. N. and König, S. and Furnstahl, R. J. and Hebeler, K.}, year={2015} }
 @article{könig_grießhammer_hammer_2015, title={The proton–deuteron system in pionless EFT revisited}, volume={42}, DOI={10.1088/0954-3899/42/4/045101}, abstractNote={We provide a detailed discussion of the low-energy proton?deuteron system in pionless effective field theory, considering both the spin-quartet and doublet S-wave channels. Extending and amending our previous work on the subject, we calculate the 3He?3H binding energy difference both perturbatively (using properly normalized trinucleon wave functions) and non-perturbatively by resumming all Coulomb diagrams in the doublet channel. Our nonperturbative result agrees well with a calculation that involves the full off-shell Coulomb T-matrix. Carefully examining the cutoff-dependence in the doublet channel, we present numerical evidence for a new three-nucleon counterterm being necessary at next-to-leading order if Coulomb effects are included. Indeed, such a term has recently been identified analytically. We furthermore make a case for a simplified Coulomb power counting that is consistent throughout the bound-state and scattering regimes. Finally, using a ?partially screened? full off-shell Coulomb T-matrix, we investigate the importance of higher-order Coulomb corrections in low-energy quartet-channel scattering.}, number={4}, journal={Journal of Physics G: Nuclear and Particle Physics}, publisher={IOP Publishing}, author={König, Sebastian and Grießhammer, Harald W and Hammer, H-W}, year={2015}, month={Jan}, pages={045101} }
 @article{hammer_könig_2014, title={Constraints on a possible dineutron state from pionless EFT}, volume={736}, DOI={10.1016/j.physletb.2014.07.015}, abstractNote={We investigate the sensitivity of the three-nucleon system to changes in the neutron–neutron scattering length to next-to-leading order in the pionless effective field theory, focusing on the triton–3He binding energy difference and neutron–deuteron elastic scattering. Due to the appearance of a proton–deuteron three-body counterterm at this order, the triton–3He binding energy difference remains consistent with the experimental value even for large positive neutron–neutron scattering lengths while the elastic neutron–deuteron scattering phase shifts are insensitive. We conclude that a bound dineutron cannot be excluded to next-to-leading order in pionless EFT.}, journal={Physics Letters B}, publisher={Elsevier BV}, author={Hammer, H.-W. and König, Sebastian}, year={2014}, month={Sep}, pages={208–213} }
 @article{vanasse_egolf_kerin_könig_springer_2014, title={He3andpdscattering to next-to-leading order in pionless effective field theory}, volume={89}, url={http://dx.doi.org/10.1103/physrevc.89.064003}, DOI={10.1103/physrevc.89.064003}, abstractNote={We study the three-body systems of ${}^{3}\mathrm{He}$ and $pd$ scattering and demonstrate, both analytically and numerically, that a new $pd$ three-body force is needed at next-to-leading order in pionless effective field theory. We also show that at leading order these observables require no new three-body force beyond what is necessary to describe $nd$ scattering. We include electromagnetic effects by iterating only diagrams that involve a single photon exchange in the three-body sector.}, number={6}, journal={Physical Review C}, publisher={American Physical Society (APS)}, author={Vanasse, Jared and Egolf, David A. and Kerin, John and König, Sebastian and Springer, Roxanne P.}, year={2014}, month={Jun} }
 @article{könig_hammer_2014, title={Precision calculation of the quartet-channelp−dscattering length}, volume={90}, DOI={10.1103/physrevc.90.034005}, abstractNote={We present a fully perturbative calculation of the quartet-channel proton--deuteron scattering length up to next-to-next-to-leading order in pionless effective field theory. We use a framework that consistently extracts the Coulomb-modified effective range function for a screened Coulomb potential in momentum space and allows for a clear linear extrapolation back to the physical limit without screening. Our result of (10.9 +/- 0.4) fm agrees with older experimental determinations of this quantity but deviates from potential-model calculations and a more recent result from Black et al., which find larger values around 14 fm. As a possible resolution to this discrepancy, we discuss the scheme dependence of Coulomb subtractions in a three-body system.}, number={3}, journal={Physical Review C}, publisher={American Physical Society (APS)}, author={König, Sebastian and Hammer, H.-W.}, year={2014}, month={Sep} }
 @article{ultraviolet extrapolations in finite oscillator bases_2014, DOI={10.1103/PhysRevC.90.064007}, abstractNote={The use of finite harmonic oscillator spaces in many-body calculations introduces both infrared (IR) and ultraviolet (UV) errors. The IR effects are well approximated by imposing a hard-wall boundary condition at a properly identified radius L_eff. We show that duality of the oscillator implies that the UV effects are equally well described by imposing a sharp momentum cutoff at a momentum Lambda_eff complementary to L_eff. By considering two-body systems with separable potentials, we show that the UV energy corrections depend on details of the potential, in contrast to the IR energy corrections, which depend only on the S-matrix. An adaptation of the separable treatment to more general interactions is developed and applied to model potentials as well as to the deuteron with realistic potentials. The previous success with a simple phenomenological form for the UV error is also explained. Possibilities for controlled extrapolations for A > 2 based on scaling arguments are discussed.}, journal={Physical Review C}, year={2014}, month={Dec} }
 @article{kã¶nig_lee_hammer_2013, title={Causality constraints for charged particles}, volume={40}, DOI={10.1088/0954-3899/40/4/045106}, abstractNote={In quantum systems with short-range interactions, causality imposes nontrivial constraints on low-energy scattering parameters. We investigate these causality constraints for systems where a long-range Coulomb potential is present in addition to a short-range interaction. The main result is an upper bound for the Coulomb-modified effective range parameter. We discuss the implications of this bound to the effective field theory for nuclear halo systems. In particular, we consider several examples of proton–nucleus and nucleus–nucleus scattering. For the bound-state regime, we find relations for the asymptotic normalization coefficients (ANCs) of nuclear halo states. As an application of these relations, we extract the ANCs of the excited 2+ and 1− states in 16O from α − 12C scattering data.}, number={4}, journal={Journal of Physics G: Nuclear and Particle Physics}, publisher={IOP Publishing}, author={König, Sebastian and Lee, Dean and Hammer, H-W}, year={2013}, pages={045106} }
 @article{elhatisari_koenig_lee_hammer_2013, title={Causality, universality, and effective field theory for van der Waals interactions}, volume={87}, ISSN={["1094-1622"]}, DOI={10.1103/physreva.87.052705}, abstractNote={We analyze low-energy scattering for arbitrary short-range interactions plus an attractive 1/r^6 tail. We derive the constraints of causality and unitarity and find that the van der Waals length scale dominates over parameters characterizing the short-distance physics of the interaction. This separation of scales suggests a separate universality class for physics characterizing interactions with an attractive 1/r^6 tail. We argue that a similar universality class exists for any attractive potential 1/r^{alpha} for alpha >= 2. We also discuss the extension to multi-channel systems near a magnetic Feshbach resonance. We discuss the implications for effective field theory with attractive singular power law tails.}, number={5}, journal={PHYSICAL REVIEW A}, publisher={American Physical Society}, author={Elhatisari, Serdar and Koenig, Sebastian and Lee, Dean and Hammer, H. -W.}, year={2013}, month={May} }
 @article{kã¶nig_hammer_2013, title={The Low-Energy p–d System in Pionless EFT}, volume={54}, DOI={10.1007/s00601-012-0351-0}, number={1-4}, journal={Few-Body Systems}, publisher={Springer-Verlag}, author={König, Sebastian and Hammer, H.-W.}, year={2013}, pages={231–234} }
 @article{koenig_lee_hammer_2012, title={Non-relativistic bound states in a finite volume}, volume={327}, ISSN={["0003-4916"]}, DOI={10.1016/j.aop.2011.12.015}, abstractNote={We derive general results for the mass shift of bound states with angular momentum ℓ≥1 in a periodic cubic box in two and three spatial dimensions. Our results have applications to lattice simulations of hadronic molecules, halo nuclei, and Feshbach molecules. The sign of the mass shift can be related to the symmetry properties of the state under consideration. We verify our analytical results with explicit numerical calculations. Moreover, we comment on the relations connecting the effective range parameter, the binding momentum of a given state and the asymptotic normalization coefficient of the corresponding wave function. We give explicit expressions for this relation in the shallow binding limit.}, number={6}, journal={ANNALS OF PHYSICS}, publisher={Elsevier }, author={Koenig, Sebastian and Lee, Dean and Hammer, H. -W.}, year={2012}, month={Jun}, pages={1450–1471} }
 @article{low-energy p-d scattering and 3he in pionless effective field theory_2011, url={http://dx.doi.org/10.1103/physrevc.83.064001}, DOI={10.1103/physrevc.83.064001}, abstractNote={We calculate low-energy proton-deuteron scattering in the framework of pionless effective field theory. In the quartet channel, we calculate the elastic scattering phase shift up to next-to-next-to-leading order in the power counting. In the doublet channel, we perform a next-to-leading-order calculation. We obtain good agreement with the available phase-shift analyses down to the scattering threshold. The phase shifts in the region of nonperturbative Coulomb interactions are calculated by using an optimized integration mesh. Moreover, the Coulomb contribution to the $^{3}\mathrm{He}$-$^{3}\mathrm{H}$ binding energy difference is evaluated in first-order perturbation theory. We comment on the implications of our results for the power counting of subleading three-body forces.}, journal={Physical Review C}, year={2011}, month={Jun} }
 @article{bour_kã¶nig_lee_hammer_meiãŸner_2011, title={Topological phases for bound states moving in a finite volume}, volume={84}, url={http://dx.doi.org/10.1103/physrevd.84.091503}, DOI={10.1103/physrevd.84.091503}, abstractNote={We show that bound states moving in a finite periodic volume have an energy correction which is topological in origin and universal in character. The topological volume corrections contain information about the number and mass of the constituents of the bound states. These results have broad applications to lattice calculations involving nucleons, nuclei, hadronic molecules, and cold atoms. We illustrate and verify the analytical results with several numerical lattice calculations.}, number={9}, journal={Physical Review D}, publisher={American Physical Society}, author={Bour, Shahin and König, Sebastian and Lee, Dean and Hammer, H.-W. and Meißner, Ulf-G.}, year={2011} }
 @article{koenig_lee_hammer_2011, title={Volume Dependence of Bound States with Angular Momentum}, volume={107}, ISSN={["1079-7114"]}, DOI={10.1103/physrevlett.107.112001}, abstractNote={We derive general results for the mass shift of bound states with angular momentum ℓ≥1 in a finite periodic volume. Our results have direct applications to lattice simulations of hadronic molecules as well as atomic nuclei. While the binding of S-wave bound states increases at finite volume, we show that the binding of P-wave bound states decreases. The mass shift for D-wave bound states as well as higher partial waves depends on the representation of the cubic rotation group. Nevertheless, the multiplet-averaged mass shift for any angular momentum ℓ can be expressed in a simple form, and the sign of the shift alternates for even and odd ℓ. We verify our analytical results with explicit numerical calculations. We also show numerically that similar volume corrections appear in three-body bound states.}, number={11}, journal={PHYSICAL REVIEW LETTERS}, publisher={American Physical Society}, author={Koenig, Sebastian and Lee, Dean and Hammer, H. -W.}, year={2011}, month={Sep} }