Finite volume effects and quark mass dependence of the N(1535) and N(1650)

For resonances decaying in a finite volume, the simple identification of state and eigenvalue is lost. The extraction of the scattering amplitude is a major challenge as we demonstrate by extrapolating the physical S_{11} amplitude of pion-nucleon scattering to the finite volume and unphysical quark masses, using a unitarized chiral framework including all next-to-leading order contact terms. We show that the pole movement of the resonances N(1535)1/2^- and N(1650)1/2^- with varying quark masses is non-trivial. In addition, there are several strongly coupled S-wave thresholds that induce a similar avoided level crossing as narrow resonances. The level spectrum is predicted for two typical lattice setups, and ways to extract the amplitude from upcoming lattice data are discussed.Comment: 8 pages, 5 .eps figure

The Optical Potential on the Lattice

The extraction of hadron-hadron scattering parameters from lattice data by using the L\"uscher approach becomes increasingly complicated in the presence of inelastic channels. We propose a method for the direct extraction of the complex hadron-hadron optical potential on the lattice, which does not require the use of the multi-channel L\"uscher formalism. Moreover, this method is applicable without modifications if some inelastic channels contain three or more particles.Comment: 26 pages, 12 figure

Causal relationship between the right auditory cortex and speech-evoked frequency-following response: Evidence from combined tDCS and EEG

Speech-evoked frequency-following response (FFR) reflects the neural encoding of speech periodic information in the human auditory systems. FFR is of fundamental importance for pitch and speech perception and serves as clinical biomarkers for various auditory and language disorders. While it is suggested that the main neural source of FFR is in the auditory brainstem, recent studies have shown a cortical contribution to FFR predominantly in the right hemisphere. However, it is still unclear whether auditory cortex and FFR are causally related. The aim of this study was to establish this causal relationship using a combination of transcranial direct current stimulation (tDCS) and scalp-recorded electroencephalography (EEG). We applied tDCS over the left and right auditory cortices in right-handed normal-hearing participants and examined the after-effects of tDCS on FFR using EEG during monaural listening to a repeatedly-presented speech syllable. Our results showed that: (1) before tDCS was applied, participants had greater FFR magnitude when they listened to speech from the left than the right ear, illustrating right-lateralized hemispheric asymmetry for FFR; (2) anodal and cathodal tDCS applied over the right, but not left, auditory cortex significantly changed FFR magnitudes compared to the sham stimulation; specifically, such after-effects occurred only when participants listened to speech from the left ear, emphasizing the right auditory cortical contributions along the contralateral pathway. The current finding thus provides the first causal evidence that validates the relationship between the right auditory cortex and speech-evoked FFR and should significantly extend our understanding of speech encoding in the brain

Constraints on the chiral unitary KˉN\bar KN amplitude from πΣK+\pi\Sigma K^+ photoproduction data

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 $\Lambda (1405)$. The narrow $\Lambda(1405)$ 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 $K^+\pi\Sigma$ 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.Comment: Version accepted for publication in Eur. Phys. A, discussion of results extende

Pion photoproduction off the proton in a gauge-invariant chiral unitary framework

We investigate pion photoproduction off the proton in a manifestly gauge-invariant chiral unitary extension of chiral perturbation theory. In a first step, we consider meson-baryon scattering taking into account all next-to-leading order contact interactions. The resulting low-energy constants are determined by a fit to s-wave pion-nucleon scattering and the low-energy data for the reaction pi- p --> eta n. To assess the theoretical uncertainty, we perform two different fit strategies. Having determined the low-energy constants, we then analyse the data on the s-wave multipole amplitudes E0+ of pion and eta photoproduction. These are parameter-free predictions, as the two new low-energy constants are determined by the neutron and proton magnetic moments.Comment: 23 pages, 17 figure

Relationship between speech-evoked neural responses and perception of speech in noise in older adults

Speech-in-noise (SPIN) perception involves neural encoding of temporal acoustic cues. Cues include temporal fine structure (TFS) and envelopes that modulate at syllable (Slow-rate ENV) and fundamental frequency (F0-rate ENV) rates. Here the relationship between speech-evoked neural responses to these cues and SPIN perception was investigated in older adults. Theta-band phase-locking values (PLV) that reflect cortical sensitivity to Slow-rate ENV and peripheral/brainstem frequency-following responses phase-locked to F0-rate ENV (FFRENV_F0) and TFS (FFRTFS) were measured from scalp-EEG responses to a repeated speech syllable in steady-state speech-shaped (SpN) and 16-speaker babble (BbN) noises. The results showed that: 1) SPIN performance and PLV were significantly higher under SpN than BbN, implying differential cortical encoding may serve as the neural mechanism of SPIN performance that varies as a function of noise types; 2) PLV and FFRTFS at resolved harmonics were significantly related to good SPIN performance, supporting the importance of phase-locked neural encoding of Slow-rate ENV and TFS of resolved harmonics during SPIN perception; 3) FFRENV_F0 was not associated to SPIN performance until audiometric threshold was controlled for, indicating that hearing loss should be carefully controlled when studying the role of neural encoding of F0-rate ENV. Implications are drawn with respect to fitting auditory prostheses

Multi-dimensional laser spectroscopy of exciton-polaritons with spatial light modulators

We describe an experimental system that allows one to easily access the dispersion curve of exciton-polaritons in a microcavity. Our approach is based on two spatial light modulators (SLM), one for changing the excitation angles (momenta), and the other for tuning the excitation wavelength. We show that with this setup, an arbitrary number of states can be excited accurately and that re-configuration of the excitation scheme can be done at high speed.Comment: 4 pages, 5 figure