Ultimate parameters of the photon collider at the ILC

At linear colliders, the e+e- luminosity is limited by beam-collision effects, which determine the required emittances of beams in damping rings (DRs). While in gamma-gamma collisions at the photon collider, these effects are absent, and so smaller emittances are desirable. In present damping rings designs, nominal DR parameters correspond to those required for e+e- collisions. In this note, I would like to stress once again that as soon as we plan the photon-collider mode of ILC operation, the damping-ring emittances are dictated by the photon-collider requirements--namely, they should be as small as possible. This can be achieved by adding more wigglers to the DRs; the incremental cost is easily justified by a considerable potential improvement of the gamma-gamma luminosity. No expert analysis exists as of yet, but it seems realistic to obtain a factor five increase of the gamma-gamma luminosity compared to the ``nominal'' DR design.Comment: Talk at LCWS06, Bangalore, India, March 2006, to be published in Indian Journal of Physics, 5 pp, Latex, 1 .eps figur

Relativistic mask method for electron momentum distributions after ionization of hydrogen-like ions in strong laser fields

Wavefunction-splitting or mask method, widely used in the non-relativistic calculations of the photoelectron angular distributions, is extended to the relativistic domain within the dipole approximation. Since the closed-form expressions for the relativistic Volkov states are not available within the dipole approximation, we build such states numerically solving a single second-order differential equation. We calculate the photoelectron energy spectra and angular distributions for highly charged ions under different ionization regimes with both the direct and the relativistic mask methods. We show that the relativistic mask method works very well and reproduces the electron energy and angular distributions calculated by the direct method in the energy range where both methods can be used. On the other hand, the relativistic mask method can be applied for longer laser pulses and/or higher photoelectron energies where the direct method may have difficulties

Restriction on the energy and luminosity of e+e- storage rings due to beamstrahlung

The role of beamstrahlung in high-energy e+e- storage-ring colliders (SRCs) is examined. Particle loss due to the emission of single energetic beamstrahlung photons is shown to impose a fundamental limit on SRC luminosities at energies 2E_0 >~ 140 GeV for head-on collisions and 2E_0 >~ 40 GeV for crab-waist collisions. With beamstrahlung taken into account, we explore the viability of SRCs in the E_0=240-500 GeV range, which is of interest in the precision study of the Higgs boson. At 2E_0=240 GeV, SRCs are found to be competitive with linear colliders; however, at 2E_0=400-500 GeV, the attainable SRC luminosity would be a factor 15-25 smaller than desired.Comment: Latex, 5 pages. v2 differs only by minor changes is abstract and introduction, one reference is added. v3 corresponds to the paper published in PR

Full one-loop QCD and electroweak corrections to sfermion pair production in γγ\gamma \gamma collisions

We have calculated the full one-loop electroweak (EW) and QCD corrections to the third generation scalar-fermion pair production processes $e^+e^- \to \gamma \gamma \to \tilde{f_i}\bar{\tilde{f_i}} (f=t,b,\tau)$ at an electron-positron linear collider(LC) in the minimal supersymmetric standard model (MSSM). We analyze the dependence of the radiative corrections on the parameters such as the colliding energy $\sqrt{\hat s}$ and the SUSY fundamental parameters $A_f$, $\tan \beta$, $\mu$, $M_{SUSY}$ and so forth. The numerical results show that the EW corrections to the squark-, stau-pair production processes and QCD corrections to the squark-pair production processes give substantial contributions in some parameter space. The EW relative corrections to squark-pair production processes can be comparable with QCD corrections at high energies. Therefore, these EW and QCD corrections cannot be neglected in precise measurement of sfermion pair productions via $\gamma\gamma$ collision at future linear colliders.Comment: to be appeared in Phys. Rev.

Low-energy structure of above-threshold-ionization electron spectra: Role of the Coulomb threshold effect

This is the publishers version, also available here: http://dx.doi.org/10.1103/PhysRevA.83.063406.Recent experimental observations of above-threshold ionization of rare gas atoms and diatomic molecules by midinfrared laser fields [C. I. Blaga et al., Nat. Phys. 5, 335 (2009); W. Quan et al., Phys. Rev. Lett. 103, 093001 (2009)] revealed a prominent maximum in the electron energy spectrum very close to the ionization threshold which is not reproduced by widely used Keldysh-Faisal-Reiss theories. We have performed fully ab initio theoretical analysis and precision calculations to explore the quantum origin of the low-energy structure (LES) observed in the experiments. Our study shows that an important role in shaping of LES is played by the effect of Coulomb attraction in the final electron state and the Coulomb threshold effect

High-order perturbation expansion of non-Hermitian Floquet theory for multiphoton and above-threshold ionization processes

This is the published version, also available here: http://dx.doi.org/10.1103/PhysRevA.61.013408.A high-order perturbation theory is presented for efficient and accurate computation of multiphoton and above-threshold ionization cross sections of atoms and molecules in weak to medium strength laser fields. The procedure is based on a Raleigh-Schrödinger perturbative expansion of the time-independent non-Hermitian Floquet Hamiltonian. The reduced Green function and generalized pseudospectral discretization techniques are extended to facilitate the calculation of complex quasienergy resonance states without the need of diagonalizing the full Floquet Hamiltonian. Explicit expressions are presented for the determination of intensity-dependent total and partial rates and electron angular distributions. The theory is applied to a case study of multiphoton detachment of H- for a range of laser frequencies (corresponding to the absorption of a minimum of two photons) and laser intensities from 107 to 1012W/cm2. It is found that a 16th-order perturbative Floquet procedure provides an excellent description of the two-photon-dominant detachment processes for laser intensity up to 2×1011W/cm2. The predicted electron angular distributions are in good agreement with recent experimental data

Multiphoton above-threshold detachment of Li-: Exterior-complex-scaling– generalized-pseudospectral method for calculations of complex-quasienergy resonances in Floquet formulation of time-dependent density-functional theory

This is the publisher's version, also available electronically from http://journals.aps.org/pra/abstract/10.1103/PhysRevA.66.043417.We extend the exterior-complex-scaling–generalized-pseudospectral (ECSGPS) method [D. A. Telnov and S. I. Chu, Phys. Rev. A 59, 2864 (1999)] to the nonperturbative calculations of complex-quasienergy resonances of many-electron quantum systems within the Floquet formulation of time-dependent density-functional theory (TDDFT) [D. A. Telnov and S. I. Chu, Chem. Phys. Lett. 264, 466 (1997)]. The ECSGPS technique appears very useful in TDDFT-Floquet calculations where the exchange-correlation potentials may exhibit quite complicated behavior as functions of the electron coordinates and cannot be easily treated by means of the uniform-complex-scaling techniques. We have applied this procedure to the study of one-photon detachment and two-photon dominant above-threshold detachment of Li- negative ions. In the one-photon case, the photodetachment cross section has been calculated as a function of the photon energy with results in good agreement with the experimental data. In the two-photon case, both the partial detachment rates and electron angular distributions for the dominant and above-threshold channels are presented for a range of laser field frequencies and intensities. Dramatic transformations of the angular distributions in the vicinity of the two-photon threshold are observed and analyzed

Exact relations of the quasienergy functional and the exchange-correlation potential from the Floquet formulation of time-dependent density functional theory

In the framework of the Floquet formulation of time-dependent density functional theory we present several exact relations involving different parts of the quasienergy functional. These relations hold when the exact densities and exchange-correlation energy functional are employed. They can be used as useful constraints and tests when searching for the approximate forms of the time-dependent exchange-correlation functionals. The general results are illustrated on an exactly soluble model, Hooke’s atom in a linearly polarized monochromatic laser field