Search

Pion electroproduction off the proton is analyzed in a new framework based on a general parametrization of transition amplitudes, including constraints from gauge invariance and threshold behavior. Data with energies $1.13~{\rm GeV}, 27 pages, 14 figures

We utilize the experimentally known difference of the $��$ separation energies of the mirror hypernuclei ${^4_��\rm He}$ and ${^4_��\rm H}$ to constrain the $��$-neutron interaction. We include the leading charge-symmetry breaking (CSB) interaction into our hyperon-nucleon interaction derived within chiral effective field theory at next-to-leading order. In particular, we determine the strength of the two arising CSB contact terms by a fit to the differences of the separation energies of these hypernuclei in the $0^+$ and $1^+$ states, respectively. By construction, the resulting interaction describes all low energy hyperon-nucleon scattering data, the hypertriton and the CSB in ${^4_��\rm He}$-${^4_��\rm H}$ accurately. This allows us to provide first predictions for the $��$n scattering lengths, based solely on available hypernuclear data., 19 pages, 2 figures, to be submitted to special issue of few-body systems "Celebrating 30 years of Steven Weinberg's papers on Nuclear Forces from Chiral Lagrangians"

We investigate the existence of bound $��$ \break states in systems with $A=4-7$ baryons using the Jacobi NCSM approach in combination with chiral NN and $��$N interactions. We find three shallow bound states for the NNN$��$ system (with $(J^��,T)=(1^+,0)$, $(0^+,1)$ and $(1^+,1)$) with quite similar binding energies. The $^5_��\mathrm{H}(\frac{1}{2}^+,\frac{1}{2})$ and $^7_��\mathrm{H}(\frac{1}{2}^+,\frac{3}{2})$ hypernuclei are also clearly bound with respect to the thresholds $^4\mathrm{He} + ��$ and $^6\mathrm{He} +��$, respectively. The binding of all these $��$ systems is predominantly due to the attraction of the chiral $��$N potential in the $^{33}S_1$ channel. A perturbative estimation suggests that the decay widths of all the observed states could be rather small., 12 pages, 2 figures

We study the unitarized meson-baryon scattering amplitude at leading order in the strangeness $S=-1$ sector using time-ordered perturbation theory for a manifestly Lorentz-invariant formulation of chiral effective field theory. By solving the coupled-channel integral equations with the full off-shell dependence of the effective potential and applying subtractive renormalization, we analyze the renormalized scattering amplitudes and obtain the two-pole structure of the $��(1405)$ resonance. We also point out the necessity of including higher-order terms., 16 pages, 3 figures, 5 tables

In this work, we analyze the semi-leptonic decays $\bar B^0/D^0 \to (a_0(980)^{\pm}\to��^{\pm}��) l^{\mp} ��$ within light-cone sum rules. The two and three-body light-cone distribution amplitudes (LCDAs) of the $B$ meson and the only available two-body LCDA of the $D$ meson are used. To include the finite-width effect of the $a_0(980)$, we use a scalar form factor to describe the final-state interaction between the $����$ mesons, which was previously calculated within unitarized Chiral Perturbation Theory. The result for the decay branching fraction of the $D^0$ decay is in good agreement with that measured by the BESIII Collaboration, while the branching fraction of the $\bar B^0$ decay can be tested in future experiments., 19 pages, 5 figures

We generalize the Jacobi no-core shell model (J-NCSM) to study double-strangeness hypernuclei. All particle conversions in the strangeness $S=-1,-2$ sectors are explicitly taken into account. In two-body space, such transitions may lead to the coupling between states of identical particles and of non-identical ones. Therefore, a careful consideration is required when determining the combinatorial factors that connect the many-body potential matrix elements and the free-space two-body potentials. Using second quantization, we systematically derive the combinatorial factors in question for $S=0,-1,-2$ sectors. As a first application, we use the J-NCSM to investigate $����$ s-shell hypernuclei based on hyperon-hyperon (YY) potentials derived within chiral effective field theory at leading order (LO) and up to next-to-leading order (NLO). We find that the LO potential overbinds $^{\text{ }\text{ }\text{ } \text{}6}_{����}\text{He}$ while the prediction of the NLO interaction is close to experiment. Both interactions also yield a bound state for $^{\text{ }\text{ }\text{ } \text{}5}_{����}\text{He}$. The $^{\text{}\text{ }\text{ }\text{}4}_{����}\text{H}$ system is predicted to be unbound., 23 pages, 3 figures

The measurements of $V_{us}$ in leptonic $(K_{��2})$ and semileptonic $(K_{l3})$ kaon decays exhibit a $3��$ disagreement, which could originate either from physics beyond the Standard Model or some large unidentified Standard Model systematic effects. Clarifying this issue requires a careful examination of all existing Standard Model inputs. Making use of a newly-proposed computational framework and the most recent lattice QCD results, we perform a comprehensive re-analysis of the electroweak radiative corrections to the $K_{e3}$ decay rates that achieves an unprecedented level of precision of $10^{-4}$, which improves the current best results by almost an order of magnitude. No large systematic effects are found, which suggests that the electroweak radiative corrections should be removed from the ``list of culprits'' responsible for the $K_{��2}$--$K_{l3}$ discrepancy., Version accepted by JHEP

In this work, we study the resonance contributions to the decay $B^-\to K^+K^-��^-$, which is dominated by the scalar $f_0(980), K_0^*(1430)$, vector $��(1450), ��(1020), K^*(892)$ and tensor $f_2(1270)$ resonances. The three-body decay is reduced to various quasi two-body decays, where the $B$ meson firstly decays into a resonance and a pion or a kaon, subsequently the resonance decays into the other two final-state mesons. The quasi two-body decays are calculated within the light-cone sum rule approach utilizing the leading twist $B$ meson light-cone distribution amplitudes. Finally, the decay branching fraction contribution from each resonance are calculated. Some of them are compatible with experiment or previous theoretical works. Including the effects of non-resonant and final-state interactions, we also evaluate the total branching fraction., 29 pages, 1 figure

Deep Learning using the eponymous deep neural networks (DNNs) has become an attractive approach towards various data-based problems of theoretical physics in the past decade. There has been a clear trend to deeper architectures containing increasingly more powerful and involved layers. Contrarily, Taylor coefficients of DNNs still appear mainly in the light of interpretability studies, where they are computed at most to first order. However, especially in theoretical physics numerous problems benefit from accessing higher orders, as well. This gap motivates a general formulation of neural network (NN) Taylor expansions. Restricting our analysis to multilayer perceptrons (MLPs) and introducing quantities we refer to as propagators and vertices, both depending on the MLP's weights and biases, we establish a graph-theoretical approach. Similarly to Feynman rules in quantum field theories, we can systematically assign diagrams containing propagators and vertices to the corresponding partial derivative. Examining this approach for S-wave scattering lengths of shallow potentials, we observe NNs to adapt their derivatives mainly to the leading order of the target function's Taylor expansion. To circumvent this problem, we propose an iterative NN perturbation theory. During each iteration we eliminate the leading order, such that the next-to-leading order can be faithfully learned during the subsequent iteration. After performing two iterations, we find that the first- and second-order Born terms are correctly adapted during the respective iterations. Finally, we combine both results to find a proxy that acts as a machine-learned second-order Born approximation., 29 pages, 4 figures, revised with more focus on neural network perturbation theory, accepted for publication in Phys. Rev. Research

The photoproduction of the $J/��$ off the proton is believed to deepen our understanding of various physics issues. On the one hand, it is proposed to provide access to the origin of the proton mass, based on the QCD multipole expansion. On the other hand, it can be employed in a study of pentaquark states. The process is usually assumed to proceed through vector-meson dominance, that is the photon couples to a $J/��$ which rescatters with the proton to give the $J/��p$ final state. In this Letter, we provide a compelling hint for and propose measurements necessary to confirm a novel production mechanism via the $��_c \bar D^{(*)}$ intermediate states. In particular, there must be cusp structures at the $��_c \bar D^{(*)}$ thresholds in the energy dependence of the $J/��$ photoproduction cross section. The same mechanism also implies the $J/��$-nucleon scattering lengths of order 1 mfm. Given this, one expects only a minor contribution of charm quarks to the nucleon mass., 6 pages, 5 figures

At low energies, the strong interaction is governed by the Goldstone bosons associated with the spontaneous chiral symmetry breaking, which can be systematically described by chiral perturbation theory. In this paper, we apply this theory to study the $��$-vacuum energy density and hence the QCD axion potential up to next-to-leading order with $N$ non-degenerate quark masses. By setting $N=3$, we then derive the axion mass, self-coupling, topological susceptibility and the normalized fourth cumulant both analytically and numerically, taking the strong isospin breaking effects into account. In addition, the model-independent part of the axion-photon coupling, which is important for axion search experiments, is also extracted from the chiral Lagrangian supplemented with the anomalous terms up to $\mathcal{O}(p^6)$., 22 pages, 1 figure, 2 tables; Version to appear in JHEP

We investigate the impact of the QCD vacuum at nonzero $��$ on the properties of light nuclei, Big Bang nucleosynthesis, and stellar nucleosynthesis. Our analysis starts with a calculation of the $��$-dependence of the neutron-proton mass difference and neutron decay using chiral perturbation theory. We then discuss the $��$-dependence of the nucleon-nucleon interaction using a one-boson-exchange model and compute the properties of the two-nucleon system. Using the universal properties of four-component fermions at large scattering length, we then deduce the binding energies of the three-nucleon and four-nucleon systems. Based on these results, we discuss the implications for primordial abundances of light nuclei, the production of nuclei in stellar environments, and implications for an anthropic view of the universe., 20 pages, 9 figures

Precision predictions combined with precise measurements are a major tool in sharpening our understanding of the fundamental laws underlying microscopic as well as macroscopic systems. Here, I present a few remarkable examples covering the fields of nuclear, particle and astrophysics., invited talk, first Joint ECFA-NuPECC-ApPEC Seminar, Paris, October 14-16, 2019 (JENAS-2019), short write-up, commissioned article for Nuclear Physics News

In this paper we propose a dispersive method to describe two-body scattering with unitarity imposed. This approach is applied to elastic $����$ scattering. The amplitudes keep single-channel unitarity and describe the experimental data well, and the low-energy amplitudes are consistent with that of chiral perturbation theory. The pole locations of the $��$, $f_0(980)$, $��(770)$ and $f_2(1270)$ and their couplings to $����$ are obtained. A virtual state appearing in the isospin-two S-wave is confirmed. The correlations between the left (and right) hand cut and the poles are discussed. Our results show that the poles are more sensitive to the right hand cut rather than the left hand cut. The proposed method could be used to study other two-body scattering processes., 10 pages, 4 figures

We re-analyze the flavor decomposition of the pion-nucleon $��$-term in the framework of baryon chiral perturbation to fourth order. We employ a covariant and the heavy baryon framework including also the low-lying decuplet. Using only continuum data, we find a small strangeness content of the proton. The uncertainties are, however, large and might be overcome by dedicated lattice QCD calculations., 31 pages, 1 figure, published version, some minor modifications

The accuracy of the lattice QCD computation of hadron-hadron scattering at low isospin depends critically on the ability to compute correlation functions with fermionic disconnected Wick contractions. This happens, for instance, in isospin $I=0$ $����$ scattering, which receives contributions from rectangular and vacuum types of contractions among other easier calculable ones. Combining L��scher's formula and partially-quenched chiral perturbation theory, we provide precise theory predictions of the discrete energy levels extracted from specific linear combinations of lattice correlation functions corresponding to various types of contractions. Expressions are provided for extracting the unphysical low-energy constants in the partially-quenched chiral perturbation theory from the energy levels for these contractions. The predictions for the rectangular and vacuum contractions may serve as solid tests of the accuracy for existing and future lattice studies of $����$ scattering., Version to appear in JHEP

This paper addresses two aspects concerning the $��$-vacuum of Quantum Chromodynamics. First, large-$N_c$ chiral perturbation theory is used to calculate the first two non-trivial cumulants of the distribution of the winding number, i.\,e. the topological susceptibility, $��_\mathrm{top}$, and the fourth cumulant, $c_4$, up to next-to-leading order. Their large-$N_c$ scaling is discussed, and compared to lattice results. It is found that $��_\mathrm{top}=\mathcal{O}(N_c^0)$, as known before, and $c_4=\mathcal{O}(N_c^{-3})$, correcting the assumption of $\mathcal{O}(N_c^{-2})$ in the literature. Second, we discuss the properties of QCD at $��\sim��$ using chiral perturbation theory for the case of $2+1$ light flavors, i.\,e. by taking the strange quark mass heavier than the degenerate up and down quark masses. It is shown that --- in accordance with previous findings for $N_f=2$ and $N_f=3$ mass-degenerate flavors --- in the region $��\sim��$ two vacuum states coexist, which become degenerate at $��=��$. The wall tension of the energy barrier between these degenerate vacua is determined as well as the decay rate of a false vacuum., Accepted for publication in JHEP. 35 pages, 5 figures

Stimulated by recent indications that the binding energy of the hypertriton could be significantly larger than so far assumed, requirements of a more strongly bound $^3_��{\rm H}$ state for the hyperon-nucleon interaction and consequences for the binding energies of $A=4,5$ and $7$ hypernuclei are investigated. As basis a $YN$ potential derived at next-to-leading order in chiral effective field theory is employed, Faddeev and Yakubovsky equations are solved to obtain the corresponding $3$- and $4$-body binding energies, respectively, and the Jacobi no-core shell model is used for $^5_��$He and $^7_��$Li. It is found that the spin-singlet $��p$ interaction would have to be much more attractive which can be, however, accommodated within the bounds set by the available $��p$ scattering data. The binding energies of the $^4_��{\rm He}$ hypernucleus are predicted to be closer to the empirical values than for $YN$ interactions that produce a more weakly bound $^3_��{\rm H}$. The quality of the description of the separation energy and excitation spectrum for $^7_��$Li remains essentially unchanged., 8 pages, 3 figures; version that was published in Phys. Lett. B

We analyze the origin of the structure observed in the reaction $J/��\to ����'��^+��^-$ for $��'��^+��^-$ 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 $J/��\to ��\bar NN \to ����'��^+��^-$. 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 $J/��\to ��\bar pp$ and $J/��\to ����'��^+��^-$ for invariant masses around the $\bar pp$ threshold. The structure seen in the $��'��^+��^-$ spectrum emerges as a threshold effect due to the opening of the $\bar pp$ channel., 9 pages, 5 figures

We study the production of the spin partner of the X(3872), which is a D^{*}\bar D^{*} bound state with quantum numbers J^{PC}=2^{++} and named X_2(4012) here, with the associated emission of a photon in electron--positron collisions. The results show that the ideal energy region to observe the X_2(4012) in e^+e^- annihilations is from 4.4~GeV to 4.5~GeV, due to the presence of the S-wave \bar D^{*} D_1(2420) and \bar D^{*} D_2(2460) thresholds, respectively. We also point out that it will be difficult to observe the \gamma X(4012) at the e^+e^- center-of-mass energy around 4.26~GeV., Comment: 7 pages, 2 figures, version accepted for publication in PLB

The reaction $e^+e^-\rightarrow ��^+_c\bar��^-_c$ is investigated at energies close to the threshold with emphasis on the role played by the $X(4630)$ resonance. The interaction in the final $��^+_c \bar��^-_c$ system, constructed within chiral effective field theory and supplemented by a pole diagram that represents a bare $X(4630)$ resonance, is taken into account rigorously. The pole parameters of the $X(4630)$ are extracted and found to be compatible with the ones of the $X(4660)$ resonance that have been established in the reaction $e^+e^- \to ��^+��^-��(2S)$. The actual result for the $X(4630)$ is $M = (4652.5\pm 3.4)$ MeV and $��= (62.6\pm 5.6)$ MeV. Predictions for the $��^+_c$ electromagnetic form factors in the timelike region are presented., 11 pages, 3 figures

The number of exotic candidates which are beyond the conventional quark model has grown dramatically during the last decades. Some of them could be viewed as analogues of the deuteron. Similarly, the existence of the triton indicates that bound states formed by three hadrons could also exist. To illustrate this possibility, we study the $DD^*K$ and $BB^*\bar{K}$ systems by using the Born-Oppenheimer Approximation. To leading order, only one-pion exchange potentials are considered, which means that the three constitutes share one virtual pion. That is similar to the role of the delocalized $��$ bond for the formation of Benzene in chemistry. After solving the Schr��dinger equation, we find two three-body $DD^*K$ and $BB^*\bar{K}$ bound states with masses $4317.92_{-4.32}^{+3.66}~\mathrm{MeV}$ and $11013.65_{-8.84}^{+8.49}~\mathrm{MeV}$, respectively. The masses of their $D\bar{D}^*K$ and $B\bar{B}^*\bar{K}$ analogues are $4317.92_{-6.55}^{+6.13}~\mathrm{MeV}$ and $11013.65_{-9.02}^{+8.68}~\mathrm{MeV}$. From the experimental side, the $D\bar{D}^*K$ bound state could be found by analyzing the current world data of the $B\to J/������K$ process by focusing on the $J/����K$ channel. Its confirmation could also help to understand the formation of kaonic nuclei in nuclear physics., 5 pages, 7 figures

In this paper we perform an amplitude analysis of $��'\to��^+��^-��$ and confront it with the latest BESIII data. Based on the final-state interaction theorem, we represent the amplitude in terms of an Omn��s function multiplied by a form factor that corresponds to the contributions from left-hand cuts and right-hand cuts in the inelastic channels. We also take into account the isospin violation effect induced by $��-��$ mixing. Our results show that the anomaly contribution is mandatory in order to explain the data. Its contribution to the decay width of $��(��'\to������)$ is larger than that induced by isospin violation. Finally we extract the pole positions of the $��$ and $��$ as well as their corresponding residues., 12 pages, 5 figures, typos corrected

We investigate the process $B_c^+\to B_s^0��^+��^0$ via $B\bar{K}^*$ rescattering. The kinematic conditions for triangle singularities are perfectly satisfied in the rescattering diagrams. A resonance-like structure around the $B\bar{K}$ threshold, which we denote as $X(5777)$, is predicted to be present in the invariant mass distribution of $B_s^0 ��^+$. Because the relative weak $B\bar{K}$ $(I=1)$ interaction does not support the existence of a dynamically generated hadronic molecule, the $X(5777)$ can be identified as a pure kinematical effect due to the triangle singularity. Its observation may help to establish a non-resonance interpretation for some $XYZ$ particles., 5 pages, 3 figures

Several theoretical groups describe the antikaon-nucleon interaction at low energies within approaches based on the chiral SU(3) dynamics and including next-to-leading order contributions. We present a comparative analysis of the pertinent models and discuss in detail their pole contents. It is demonstrated that the approaches lead to very different predictions for the $K^{-}p$ amplitude extrapolated to subthreshold energies as well as for the $K^{-}n$ amplitude. The origin of the poles generated by the models is traced to the so-called zero coupling limit, in which the inter-channel couplings are switched off. This provides new insights into the pole contents of the various approaches. In particular, different concepts of forming the $\Lambda(1405)$ resonance are revealed and constraints related to the appearance of such poles in a given approach are discussed., Comment: 24 pages, 15 figures, to appear in Nuclear Physics A special issue on Strangeness and Charm Nuclear Physics; v2 - several paragraphs modified or extended, version accepted for publication

We study the dipion transitions $��(4S) \rightarrow ��(nS) ��^+��^-$ $(n=1,2)$. In particular, we consider the effects of the two intermediate bottomoniumlike exotic states $Z_b(10610)$ and $Z_b(10650)$ as well as bottom meson loops. The strong pion-pion final-state interactions, especially including channel coupling to $K\bar{K}$ in the $S$-wave, are taken into account model-independently by using dispersion theory. Based on a nonrelativistic effective field theory we find that the contribution from the bottom meson loops is comparable to those from the chiral contact terms and the $Z_b$-exchange terms. For the $��(4S) \rightarrow ��(2S) ��^+��^-$ decay, the result shows that including the effects of the $Z_b$-exchange and the bottom meson loops can naturally reproduce the two-hump behavior of the $����$ mass spectra. Future angular distribution data are decisive for the identification of different production mechanisms. For the $��(4S) \rightarrow ��(1S) ��^+��^-$ decay, we show that there is a narrow dip around 1 GeV in the $����$ invariant mass distribution, caused by the final-state interactions. The distribution is clearly different from that in similar transitions from lower $��$ states, and needs to be verified by future data with high statistics. Also we predict the decay width and the dikaon mass distribution of the $��(4S) \rightarrow ��(1S) K^+ K^-$ process., 25 pages, 8 figures, predictions of the decay width and the dikaon mass distribution of the $\Upsilon(4S) \rightarrow \Upsilon(1S) K^+ K^-$ process added, more discussions added

We calculate the width of the delta resonance at leading two-loop order in baryon chiral perturbation theory. This gives a correlation between the leading pion-nucleon-delta and pion-delta couplings, which is relevant for the analysis of pion-nucleon scattering and other processes., 7 pages, 3 figures

New data on pion-photoproduction off the proton have been included in the partial wave analyses Bonn-Gatchina and SAID and in the dynamical coupled-channel approach J��lich-Bonn. All reproduce the recent new data well: the double polarization data for E, G, H, P and T in $��p \to ��^0 p$ from ELSA, the beam asymmetry $��$ for $��p \to ��^0 p$ and $��^+ n$ from Jefferson Laboratory, and the precise new differential cross section and beam asymmetry data $��$ for $��p \to ��^0 p$ from MAMI. The new fit results for the multipoles are compared with predictions not taking into account the new data. The mutual agreement is improved considerably but still far from being perfect.

We investigate the $a_0(980)$ resonance within chiral effective field theory through a three-coupled-channel analysis, namely $����$, $K\bar{K}$ and $����'$. A global fit to recent lattice finite-volume energy levels from $����$ scattering and relevant experimental data on a $����$ event distribution and the $����\to����$ cross section is performed. Both the leading and next-to-leading-order analyses lead to similar and successful descriptions of the finite-volume energy levels and the experimental data. However, these two different analyses yield different $����$ scattering phase shifts for the physical masses for the $��, K, ��$ and $��'$ mesons. The inelasticities, the pole positions in the complex energy plane and their residues are calculated both for unphysical and physical meson masses., 34 pages, 14 figures, 2 tables. To match the published version in PRD

The $\overline{\mbox{P}}$ANDA experiment together with the high quality antiproton beam at HESR will be a powerful tool to address fundamental questions of hadron physics in the charm and multi-strange hadron sector. In connection with the recent data in the hidden charm sector, $\overline{\mbox{P}}$ANDA will be able to deliver decisive contributions to this field, due to the complementarity of the $\overline{p} p$ entrance channel and the capabilities of the combined storage ring and detector system under construction., 4 pages, 1 figure

A systematic analysis of the near-threshold enhancement in the $\bar pp$ invariant mass spectrum seen in the decay reactions $J/��\to x \bar pp$ and $��(3686) \to x \bar pp$ $(x = ��,\, ��,\, ��,\, ��,\, ��)$ is presented. The enhancement is assumed to be due to the $\bar NN$ final-state interaction (FSI) and the pertinent FSI effects are evaluated in an approach that is based on the distorted-wave Born approximation. For the $\bar NN$ interaction a recent potential derived within chiral effective field theory and fitted to results of a partial-wave analysis of $\bar pp$ scattering data is considered and, in addition, an older phenomenological model constructed by the J��lich group. It is shown that the near-threshold spectrum observed in various decay reactions can be reproduced simultaneously and consistently by our treatment of the $\bar pp$ FSI. It turns out that the interaction in the isospin-1 $^1S_0$ channel required for the description of the $J/��\to ��\bar pp$ decay predicts a $\bar NN$ bound state., 13 pages, 12 figures

Making use of a recently proposed formalism, we analyze the composite nature of the $P_c(4450)$ resonance observed by LHCb. We show that the present data suggest that this state is almost entirely made of a $��_{c1}$ and a proton, due to the close proximity to this threshold. This also suppresses the decay modes into other, lighter channels, in our study represented by $J/��p$. We further argue that this is very similar to the case of the scalar meson $f_0(980)$ which is located closely to the $K\bar K$ threshold and has a suppressed decay into the lighter $����$ channel., 6 pages, 2 tables. One more grant is acknowledged

We present a determination of the pion-nucleon ($��N$) $��$-term $��_{��N}$ based on the Cheng-Dashen low-energy theorem (LET), taking advantage of the recent high-precision data from pionic atoms to pin down the $��N$ scattering lengths as well as of constraints from analyticity, unitarity, and crossing symmetry in the form of Roy-Steiner equations to perform the extrapolation to the Cheng-Dashen point in a reliable manner. With isospin-violating corrections included both in the scattering lengths and the LET, we obtain $��_{��N}=(59.1\pm 1.9\pm 3.0)$ MeV $=(59.1\pm 3.5)$ MeV, where the first error refers to uncertainties in the $��N$ amplitude and the second to the LET. Consequences for the scalar nucleon couplings relevant for the direct detection of dark matter are discussed., 6 pages, 1 figure; title changed by journal, version to be published in PRL

We calculate the shape of the $����$ and $\bar K N$ invariant mass distributions in the $��_b \to J/��\, ����$ and $��_b \to J/��\,\bar K N$ decays that are dominated by the $��(1405)$ resonance. The weak interaction part is the same for both processes and the hadronization into the different meson-baryon channels in the final state is related by SU(3) symmetry. The most important feature is the implementation of the meson-baryon final-state interaction using two chiral unitary models from different theoretical groups. Both approaches give a good description of antikaon-nucleon scattering data, the complex energy shift in kaonic hydrogen and the line shapes of $����K$ in photoproduction, based on the two-pole scenario for the $��(1405)$. We find that this reaction reflects more the higher mass pole and we make predictions of the line shapes and relative strength of the meson-baryon distributions in the final state., 9 pages, 4 figures

We derive the pion mass and the elastic pion-pion scattering amplitude in the QCD theta-vacuum up to next-to-leading order in chiral perturbation theory. Using the modified inverse amplitude method, we study the theta-dependence of the mass and width of the light scalar meson sigma(500) and the vector meson rho(770)., 11 pages, 3 figures

Within the framework of dispersion theory, we analyze the dipion transitions between the lightest $��$ states, $��(nS) \rightarrow ��(mS) ����$ with $m < n \leq 3$. In particular, we consider the possible effects of two intermediate bottomoniumlike exotic states $Z_b(10610)$ and $Z_b(10650)$. The $����$ rescattering effects are taken into account in a model-independent way using dispersion theory. We confirm that matching the dispersive representation to the leading chiral amplitude alone cannot reproduce the peculiar two-peak $����$ mass spectrum of the decay $��(3S) \rightarrow ��(1S) ����$. The existence of the bottomoniumlike $Z_b$ states can naturally explain this anomaly. We also point out the necessity of a proper extraction of the coupling strengths for the $Z_b$ states to $��(nS)��$, which is only possible if a Flatt��-like parametrization is used in the data analysis for the $Z_b$ states., 21 pages, 6 figures. The final version published in Phys. Rev. D 93, 034030 (2016)

Using the non-relativistic effective field theory framework in a finite volume, we discuss the extraction of the $��N��^*$ transition form factors from lattice data. A counterpart of the L��scher approach for the matrix elements of unstable states is formulated. In particular, we thoroughly discuss various kinematic settings, which are used in the calculation of the above matrix element on the lattice. The emerging L��scher-Lellouch factor and the analytic continuation of the matrix elements into the complex plane are also considered in detail. A full group-theoretical analysis of the problem is made, including the partial-wave mixing and projecting out the invariant form factors from data., 29 pages, 5 figures. Right-hand side of Eq. (4.13) is corrected by the normalization factor $V^{-1/2}$ and all related formulas namely, Eqs. (4.15), (4.16), (4,17), (4.21), (4.36), (5.1), (5.3) accordingly

The existence of baryon-baryon bound states in the strangeness sector is examined in the framework of SU(3) chiral effective field theory. Specifically, the role of SU(3) symmetry breaking contact terms that arise at next-to-leading order in the employed Weinberg power counting scheme is explored. We focus on the 1S0 partial wave and on baryon-baryon channels with maximal isospin since in this case there are only two independent SU(3) symmetry breaking contact terms. At the same time, those are the channels where most of the bound states have been predicted in the past. Utilizing $pp$ phase shifts and $��^+ p$ cross section data allows us to pin down one of the SU(3) symmetry breaking contact terms and a clear indication for the decrease of attraction when going from the NN system to strangeness S=-2 is found, which rules out a bound state for $����$ with isospin I=2. Assuming that the trend observed for S=0 to S=-2 is not reversed when going to $����$ and $����$ makes also bound states in those systems rather unlikely., 10 pages, 4 figures

A chiral unitary approach for antikaon-nucleon scattering in on-shell factorization is studied. We find multiple sets of parameters for which the model describes all existing hadronic data similarly well. We confirm the two-pole structure of the $��(1405)$. The narrow $��(1405)$ pole appears at comparable positions in the complex energy plane, whereas the location of the broad pole suffers from a large uncertainty. In the second step, we use a simple model for photoproduction of $K^+����$ off the proton and confront it with the experimental data from the CLAS collaboration. It is found that only a few of the hadronic solutions allow for a consistent description of the CLAS data within the assumed reaction mechanism., Version accepted for publication in Eur. Phys. A, discussion of results extended

The reaction pi N -> pi pi N is studied at tree level up to next-to-leading order in the framework of manifestly covariant baryon chiral perturbation theory with explicit Delta(1232) degrees of freedom. Using total cross section data to determine the relevant low-energy constants, predictions are made for various differential as well as total cross sections at higher energies. A detailed comparison of results based on the heavy-baryon and relativistic formulations of chiral perturbation theory with and without explicit Delta degrees of freedom is given., 30 pages, 13 figures

The possibility of imposing partially twisted boundary conditions in the lattice study of the resonance states is investigated by using the effective field theory (EFT) methods. In particular, it is demonstrated that - in certain cases - it is possible to use partial twisting even in the presence of the quark annihilation diagrams., Presented at the 31st International Symposium on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, Germany, reference corrected in the replaced version

We analyse the $\overline B_s^0\to K^+l^-\bar ��$ and $\overline B_s^0\to K^{*+}(\to K��) \ell^-\bar ��$ decays that are valuable for extracting the CKM matrix element $|V_{ub}|$. We calculate the differential and integrated partial widths in units of $|V_{ub}|^2$ based on various calculations of hadronic form factors and in particular the latest Lattice QCD calculation of the $B_s\to K^*$ form factors. For the decay $\overline B_s^0 \to K��\ell\bar ��$, we formulate the general angular distributions with the inclusion of the various partial-wave $K��$ contributions. Using the results for the $K��$ scalar form factor calculated from unitarized chiral perturbation theory, we explore the S-wave effects on angular distribution variables and demonstrate that they may not be negligible, considering the high precision expected in future measurements. We also briefly discuss the impact of the S-wave $����$ contributions in the $B^-\to ��^+��^-\ell \bar ��$ decay and provide estimates for the mode $B^-\to K^+K^-\ell \bar ��$. The studies of these channels in future can not only be used to determine $|V_{ub}|$, but may also provide valuable information on the $K��$ and $����$ phase shifts., 1+30 pages, 13 figures, modified discussion on the B to \pi \pi l\nu

Hadron-hadron scattering lengths are fine probes of our understanding of nonperturbative QCD. I discuss the status of a variety of scattering processes sensitive to the spontaneous and explicit chiral symmetry breaking of QCD, such as pion-pion, pion-kaon, pion-nucleon, antikaon-nucleon and Goldstone boson scattering off D-mesons. The fruitful interplay of theory, experiment and lattice QCD is emphasized. I point out what has to be done in these fields to gain further insight into these fundamental parameters., Plenary talk, The 7th International Workshop on Chiral Dynamics, August 6 -10, 2012, Jefferson Lab, Newport News, Virginia, USA, to appear in the proceedings, references updated

The near-threshold behavior of the ppbar invariant mass spectrum from the psi(3686) -> gamma ppbar decay reported recently by the BESIII Collaboration is analyzed. The enhancement in the ppbar invariant mass spectrum near threshold is nicely reproduced by the ppbar final-state interaction based on the isospin averaged 1S0 partial-wave amplitude as predicted by the Julich nucleon--antinucleon model. Contributions from the f_2(1910) or f_2(1950) mesons, as promoted in earlier works, are not needed., 3 pages, 3 figures, chi^2 for the results added, to be published in Phys. Rev. D

We perform a combined analysis of antikaon-nucleon scattering cross sections and the recent SIDDHARTA kaonic hydrogen data in the framework of a coupled-channel Bethe-Salpeter approach at next-to-leading order in the chiral expansion of the effective potential. We find a precise description of the antikaon-proton scattering amplitudes and are able to extract accurate values of the scattering lengths, a0=-1.81^+0.30_-0.28 + i 0.92^+0.29_-0.23 fm, a1=+0.48^+0.12_-0.11 + i 0.87^+0.26_-0.20 fm. We also discuss the two-pole structure of the Lambda(1405)., 7 pages, 4 figures

Although the analysis of the BaBar Collaboration prefers J^P=0^+ for the X(3915), it is difficult to assign the X(3915) to the ��_{c0}(2P). We show that there is an indication of the ��_{c0}(2P) with a mass around 3840 MeV and width of about 200 MeV in the Belle and BaBar data for ����--> D\bar D., 6 pages, 1 figure

The Belle Collaboration observed an enhancement called X(4630) in the Lambda_c^+ Lambda_c^- mass distribution using initial state radiation. We demonstrate that the enhancement could be consistent with the psi'f_0(980) molecular picture of the Y(4660) taking into account the Lambda_c^+ Lambda_c^- final state interaction. To test the hypothesis that the X(4630) and Y(4660) are the same molecular state, we give predictions for its spin partner, the eta_c'f_0(980) molecule. High statistic measurements of the B decays into the K Lambda_c^+ Lambda_c^- and K eta_c' pi^+ pi^- are strongly recommended., 9 pages

We evaluate the polarization observables I^S and I^C for the reaction gamma p --> pi^0 eta p, using a chiral unitary framework developed earlier. The I^S and I^C observables have been recently measured for the first time by the CBELSA/TAPS collaboration. The theoretical predictions of I^S and I^C, given for altogether 18 angle dependent functions, are in good agreement with the measurements. Also, the asymmetry dSigma/dcos(theta) evaluated here agrees with the data. We show the importance of the Delta(1700)D33 resonance and its S-wave decay into eta Delta(1232). The result can be considered as a further confirmation of the dynamical nature of this resonance. At the highest energies, deviations of the predictions from the data start to become noticeable, which leaves room for additional processes and resonances such as a Delta(1940)D33. We also point out how to further improve the calculation., Version accepted for publication by the European Physical Journal A, 9 pages, 7 figures

We show that in the transitions psi' -> h_c ��^0 and eta_c' -> chi_{c0} pi^0 the contributions from charmed meson loops are highly suppressed, in contrast to various other charmonium decays. We calculate the width of the psi' -> h_c pi^0, which agrees with the recent BES-III data, and predict the width of the eta_c' -> chi_{c0} pi^0, ��(eta_c' -> chi_{c0} pi^0) = 1.5\pm0.4 keV. A confirmation of this prediction would also provide additional support for a recent analysis of psi' -> J/psi pi^0 (eta), where loops are claimed to play a prominent role., 7 pages, 1 figure. Version accepted for publication in Phys. Rev. D

We re-evaluate the electromagnetic corrections to eta --> 3 pi decays at next-to-leading order in the chiral expansion, arguing that effects of order e^2(m_d-m_u) disregarded so far are not negligible compared to other contributions of order e^2 times a light quark mass. Despite the appearance of the Coulomb pole in eta --> pi+ pi- pi0 and cusps in eta --> 3 pi0, the overall corrections remain small., 9 pages, 5 figures, talk given at 6th International Workshop on Chiral Dynamics, Bern, Switzerland, July 6-10, 2009