Free Meson Spectral Functions on the Lattice

We present results from an analytic calculation of thermal meson spectral functions in the infinite temperature (free field) limit. We compare spectral functions for various lattice fermion formulations used at present in studies of in-medium properties of hadrons based on the maximum entropy method (MEM). In particular, we will present a new calculation of spectral functions performed with extended quark sources.Comment: 3 pages, Lattice2003(nonzero

Probing Higgs-sector CP Violation at a Photon Collider

In this review we demonstrate physics potential of a photon linear collider by studying the neutral Higgs-boson sector of the MSSM in which interesting CP-violating Higgs mixing could arise via radiative corrections.Comment: 18 pages, 8 figures, 1 table, invited article by Modern Physics Letters A (review section), added reference

Probing the CP nature of the Higgs bosons by top-pair production at photon linear colliders

We study effects of heavy Higgs bosons on the top-pair production process at photon linear colliders. The interference patterns between the resonant Higgs-production amplitudes and the continuum QED amplitudes are examined. The patterns tell us not only the CP nature of the Higgs bosons but also the phase of the $\gamma\gamma$--Higgs vertex which gives new information about the Higgs couplings to new charged particles. We point out that it is necessary to use circularly polarized photon beams to produce efficiently heavy Higgs bosons whose masses exceed the electron beam energy, and show that the above interference patterns of the production amplitudes can be studied by observing top decay angular distributions. Analytic expressions for the helicity amplitudes for the sequential process $\gamma\gamma \to t \bar{t} \to (bW^+) (\bar{b}W^-) \to (b f_1 \bar{f}_2) (\bar{b} f_3 \bar{f}_4)$ are presented in terms of the generic $\gamma\gamma \to t \bar{t}$ production amplitudes.Comment: 34 pages, LATEX file with 6 PS figures, comments adde

Charged Higgs Production in Association with W Boson at Photon Colliders

It is important to explore the Higgs sector in order to identify the model beyond the standard model. We study the charged Higgs production in the $\gamma\gamma$ mode of a linear collider (LC) with 1000 GeV center of mass energy. We show that the cross sections for the $\gamma \gamma \to H^\pm W^\mp$ processes can be significantly enhanced in the two Higgs doublet model (THDM). The cross section can reach 0.1 - 100 fb which is comparable to other charged Higgs boson production processes at a photon collider. While for other processes the cross sections are too small for $m_H^\pm \geq 500$ GeV, $0.1 - 100$ fb can be expected in the $\gamma\gamma \to H^\pm W^\mp$ processes for $m_H^\pm \geq 570$ GeV when $m_{A^0}=800$ GeV. Therefore, even if the charged Higgs bosons can not be detected at the Large Hadron Collider (LHC), and even if the charged Higgs bosons are too heavy to be detected in other charged Higgs boson production processes at the LC, it may be possible to detect them in this process.Comment: To appear in the proceedings of 2005 International Linear Collider Workshop (LCWS 2005), Stanford, California, 18-22 Mar 200

Excited D-branes and Supergravity Solutions

We investigate the general solution with the symmetry ISO(1,p)xSO(9-p) of Type II supergravity (the three-parameter solution) from the viewpoint of the superstring theory. We find that one of the three parameters (c_1) is closely related to the ``dilaton charge'' and the appearance of the dilaton charge is a consequence of deformations of the boundary condition from that of the boundary state for BPS D-branes. We give three examples of the deformed D-branes by considering the tachyon condensation from systems of D-\bar{D}p-branes, unstable D9-branes and unstable D-instantons to the BPS saturated Dp-branes, respectively. We argue that the deformed systems are generally regarded as tachyonic and/or massive excitations of the open strings on Dp-\bar{D}p-brane systems.Comment: 29 pages, 6 figures, LaTeX2e, typos corrected, references adde

Secondary phi meson peak as an indicator of QCD phase transition in ultrarelativistic heavy ion collisions

In a previous paper, we have shown that a double phi peak structure appears in the dilepton invariant mass spectrum if a first order QCD phase transition occurs in ultrarelativistic heavy ion collisions. Furthermore, the transition temperature can be determined from the transverse momentum distribution of the low mass phi peak. In this work, we extend the study to the case that a smooth crossover occurs in the quark-gluon plasma to the hadronic matter transition. We find that the double phi peak structure still exists in the dilepton spectrum and thus remains a viable signal for the formation of the quark-gluon plasma in ultrarelativistic heavy ion collisions.Comment: 8 pages, 9 uuencoded postscript figures included, Latex, LBL-3572

Studying possible CP-violating Higgs couplings through top-quark pair productions at muon colliders

We study possible anomalous CP-violating Higgs couplings to mu mu-bar and t t-bar fully model-independent way through top-quark pair productions at muon colliders. Assuming additional non-standard neutral Higgs bosons, whose couplings with top-quark and muon are expressed in the most general covariant form, we carry out analyses of effects which they are expected to produce via CP-violating asymmetries and also the optimal-observable (OO) procedure under longitudinal and transverse muon polarizations. We find the measurement of the asymmetry for longitudinal beam polarization could be useful to catch some signal of CP violation, and an OO analysis might also be useful if we could reduce the number of unknown parameters with a help of other experiments and if the size of the parameters is at least O(1) ~ O(10).Comment: Final version (to appear in JHEP

Stringy Derivation of Nahm Construction of Monopoles

We derive the Nahm construction of monopoles from exact tachyon condensation on unstable D-branes. The Dirac operator used in the Nahm construction is identified with the tachyon profile in our D-brane approach, and we provide physical interpretation of the procedures Nahm gave. Crucial is the introduction of infinite number of brane-antibranes from which arbitrary D-brane can be constrcuted, exhibitting a unified view of various D-branes. We explicitly show the equivalence of the D3-brane boundary state with the monopole profile and the D1-brane boundary state with the Nahm data as transverse scalars.Comment: 18 pages, 4 eps figures, JHEP style, comments about low energy limits added, references adde

Equation of state of strongly coupled Hamiltonian lattice QCD at finite density

We calculate the equation of state of strongly coupled Hamiltonian lattice QCD at finite density by constructing a solution to the equation of motion corresponding to an effective Hamiltonian using Wilson fermions. We find that up to and beyond the chiral symmetry restoration density the pressure of the quark Fermi sea can be negative indicating its mechanical instability. This result is in qualitative agreement with continuum models and should be verifiable by future numerical simulations.Comment: 14 pages, 2 EPS figures. Revised version - added discussion on the equation of stat