The effects of confinement resonances on photoelectron group delay (Wigner time delay) following ionization of an atom encapsulated inside a C60 cage have been studied theoretically using both relativistic and non-relativistic random phase approximations. The results indicate clearly the resonant character of the confinement oscillations in time delay of the 4d shell of Xe@C60 and present a most direct manifestation of Wigner time delay. These oscillations were missed in a previous theoretical investigation of Ar@C60 [PRL 111, 203003 (2013)]. PACS numbers: 32.80.Rm 32.80.Fb 42.50.Hz Unprecedented advances in experimental techniques in measuring time intervals at the attosecond level [1] have engendered the ability to scrutinize the time delay in photoionization of atomic systems in the laboratory [2][3][4], thereby allowing us to probe the fundamental process of photoionization in the time domain. Specifically, using attosecond pulses of electromagnetic radiation, the time difference between the emergence of photoelectrons from two neighboring atomic subshells has been measured both in Ne [3] and Ar [4, 5]. These experimental results have stimulated a host of theoretical calculations to explain and to further explore this phenomenon [6][7][8][9]. This is of great interest, not only as a new way to study a fundamental process of nature, but also as an outstanding, unique opportunity towards a deeper understanding of the most informative parameter of the process, the photoionization amplitude. This is because the time delay is related to the energy derivative of the phase of the amplitude driving the process [10]. Indeed, to date, the only method for getting the maximum experimental information on photoionization lies through a set of measurements of total and differential photoionization cross sections, but allows only the absolute values and relative phases of matrix elements to be deduced; this is known as a complete photoionization experiment [11]. Time delay investigations, however, go beyond the complete experiment strategy and yield the derivative of the phase with respect to the photoelectron energy. Time delay investigations, thus, provide a new avenue to discern the characteristics of the basic physical quantity -the photoionization amplitude -and, thus, of the photoionization phenomenon itself. It is the ultimate aim of this paper to promote the expansion of time delay studies towards situations where they have not yet been exploited and where novel effects might occur -to atoms under confinement.The theory of time delay in physics was developed some time ago [12] and was originally envisioned as a way to study resonances -the temporary trapping of one (or more) electrons in a quasi-bound state or a potential well. Indeed, the Breit-Wigner formula of resonant scattering τ = 2/Γ equates the time delay τ with the resonant width Γ at half maximum of the cross-section [13]. Resonances are ubiquitous in photoionization of atoms, and these resonances can be of different natures: inner-shell excitations, tw...

Time delay of photoemission from valence ns, np 3/2 , and np 1/2 subshells of noble-gas atoms is theoretically scrutinized within the framework of the dipole relativistic random phase approximation. The focus is on the variation of time delay in the vicinity of the Cooper minima in photoionization of the outer subshells of neon, argon, krypton, and xenon, where the corresponding dipole matrix element changes its sign while passing through a node. It is revealed that the presence of the Cooper minimum in one photoionization channel has a strong effect on time delay in other channels. This is shown to be due to interchannel coupling.

We conduct a systematic study of the dipole phase and the photoelectron group delay (Wigner time delay) in inner shell photoionization of noble gas atoms from Ne to Xe. Our study encompasses the tender x-ray spectral range and extends to 1 keV photoelectron energy. We employ both the relativistic and non-relativistic versions of the random phase approximation with exchange. We identify the long range Coulomb and short range Hartree-Fock contributions to the dipole phase which governs the Wigner time delay variation from the threshold to the whole considered range of photoelectron energies.

The shorter latency and increased amplitude of cerebral evoked potential after rectal stimulation in patients with irritable bowel syndrome compared to controls provide objective evidence supporting visceral afferent hypersensitivity as the underlying mechanism in irritable bowel syndrome.

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