Symmetries of Two Higgs Doublet Model and CP violation

We use the invariance of physical picture under a change of Lagrangian, the reparametrization invariance in the space of Lagrangians and its particular case -- the rephrasing invariance, for analysis of the two-Higgs-doublet extension of the SM. We found that some parameters of theory like tan beta are reparametrization dependent and therefore cannot be fundamental. We use the Z2-symmetry of the Lagrangian, which prevents a phi_1 phi_2 transitions, and the different levels of its violation, soft and hard, to describe a physical content of the model. In general, the broken Z2-symmetry allows for a CP violation in the physical Higgs sector. We argue that the 2HDM with a soft breaking of Z2-symmetry is a natural model in the description of EWSB. To simplify an analysis we choose among different forms of Lagrangian describing the same physical reality a specific one, in which the vacuum expectation values of both Higgs fields are real. A possible CP violation in the Higgs sector is described by using a two-step procedure with the first step identical to a diagonalization of mass matrix for CP-even fields in the CP conserved case. We find very simple necessary and sufficient condition for a CP violation in the Higgs sector. We determine the range of parameters for which CP violation and Flavor Changing Neutral Current effects are naturally small,what corresponds to a small dimensionless mass parameter nu= Re m_{12}^2/(2v1v2). We discuss how for small nu some Higgs bosons can be heavy, with mass up to about 0.6 TeV, without violating of the unitarity constraints. We discuss main features of the large nu case, which corresponds for nu -> infty to a decoupling of heavy Higgs bosons.Comment: 27 pages, extended discussion, references added, one figure, Revtex

Possible Odderon discovery at HERA via charge asymmetry in the diffractive pi+pi- production

We discuss how the evasive Odderon signal can be enhanced by final state interactions. We suggest the charge asymmetry of pion spectra in diffractive pi+pi- photoproduction as a promising signature of the Odderon exchange.Comment: 4 pages, To appear in Proceedings of the 9th International Workshop on Deep Inelastic Scattering (DIS2001), Bologna, Italy, 27 Apr. - 1 May 200

Supersymmetric Signatures at an eeγ\gamma Collider

High energy electron-photon colliders provide unique opportunities for probing physics beyond the standard model. We have studied the experimental signatures for two supersymmetric scenarios, with the lightest supersymmetric particle (LSP) being either the lightest neutralino or the gravitino. In the ``neutralino LSP'' scenario favored by the minimal supersymmetric standard model (MSSM), it is found that some basic parameters of the model, $\mu$, $\tan\beta$, $M_1$ and $M_2$, may be uniquely determined from the outgoing electron energy spectrum without assuming high scale unification of the masses or couplings. In the ``gravitino LSP'' scenario which occurs naturally in models of low energy dynamical supersymmetry breaking, it is possible to have background-free signatures if the next-to-lightest supersymmetric particle (NLSP) has a long decay length. In cases that the NLSP decays quickly, ways to distinguish among the experimental signatures of the two scenarios and of the standard model (SM) background are discussed.Comment: 14 pages, LaTex file, 3 figure

The Q2Q^2 dependence of the hard diffractive photoproduction of vector meson or photon and the range of pQCD validity

We consider two coupled problems. We study the dependence on photon virtuality $Q^2$ for the semihard quasi--elastic photoproduction of neutral vector mesons on a quark, gluon or real photon (at $s\gg p_{\bot}^2,\;Q^2; \; p_{\bot}^2\gg \mu^2 \approx (0.3$ GeV)$^2$). To this end we calculate the corresponding amplitudes (in an analytical form) in the lowest nontrivial approximation of perturbative QCD. It is shown that the amplitude for the production of light meson varies very rapidly with the photon virtuality near $Q^2=0$. We estimate the bound of the pQCD validity region for such processes. For the real incident photon the obtained bound for the $\rho$ meson production is very high. This bound decreases fast with the increase of $Q^2$, and we expect that the virtual photoproduction at HERA gives opportunity to test the pQCD results. The signature of this region is discussed. For the hard Compton effect the pQCD should work good at not too high $p_{\bot}$, and this effect seems measurable at HERA.Comment: ReVTeX, 36 pages, 5 Postscript figures, uses epsf.st

Lessons from All Logs Summation in Yukawa Theories

Some features of old results in the total summation of all logarithmic contributions of all diagrams in Yukawa theory are presented. We discuss some lessons from this picture for the description of Pomeron, odderon, etc. in QCD.Comment: 6 pages, 2 figure

High Energy Photon-Photon Collisions at a Linear Collider

High intensity back-scattered laser beams will allow the efficient conversion of a substantial fraction of the incident lepton energy into high energy photons, thus significantly extending the physics capabilities of an electron-electron or electron-positron linear collider. The annihilation of two photons produces C=+ final states in virtually all angular momentum states. The annihilation of polarized photons into the Higgs boson determines its fundamental two-photon coupling as well as determining its parity. Other novel two-photon processes include the two-photon production of charged lepton pairs, vector boson pairs, as well as supersymmetric squark and slepton pairs and Higgstrahlung. The one-loop box diagram leads to the production of pairs of neutral particles. High energy photon-photon collisions can also provide a remarkably background-free laboratory for studying possibly anomalous $W W$ collisions and annihilation. In the case of QCD, each photon can materialize as a quark anti-quark pair which interact via multiple gluon exchange. The diffractive channels in photon-photon collisions allow a novel look at the QCD pomeron and odderon. Odderon exchange can be identified by looking at the heavy quark asymmetry. In the case of electron-photon collisions, one can measure the photon structure functions and its various components. Exclusive hadron production processes in photon-photon collisions test QCD at the amplitude level and measure the hadron distribution amplitudes which control exclusive semi-leptonic and two-body hadronic B-decays.Comment: Invited talk, presented at the 5th International Workshop On Electron-Electron Interactions At TeV Energies, Santa Cruz, California, 12-14 December 200

Some combinatorial identities related to commuting varieties and Hilbert schemes

In this article we explore some of the combinatorial consequences of recent results relating the isospectral commuting variety and the Hilbert scheme of points in the plane

Superfluidity of metastable bulk glass para-hydrogen at low temperature

Molecular para-hydrogen has been proposed theoretically as a possible candidate for superfluidity, but the eventual superfluid transition is hindered by its crystallization. In this work, we study a metastable non crystalline phase of bulk p-H2 by means of the Path Integral Monte Carlo method in order to investigate at which temperature this system can support superfluidity. By choosing accurately the initial configuration and using a non commensurate simulation box, we have been able to frustrate the formation of the crystal in the simulated system and to calculate the temperature dependence of the one-body density matrix and of the superfluid fraction. We observe a transition to a superfluid phase at temperatures around 1 K. The limit of zero temperature is also studied using the diffusion Monte Carlo method. Results for the energy, condensate fraction, and structure of the metastable liquid phase at T=0 are reported and compared with the ones obtained for the stable solid phase.Comment: 10 pages, accepted for publication in Phys. Rev.

Distinguishing technicolor models via tt-bar productions at polarized photon colliders

We study top quark pair productions at a polarized photon collider from an e(+)e(-) linear collider (LC) in various improved technicolor model, namely, the one-family walking technicolor model, the top-color-assisted technicolor model, and the top-color-assisted multiscale technicolor model. Recent constraint on the top-pion mass from the precision data of R(b) is considered. It is shown that, considering only the statistical errors, a polarized photon collider from a 500 GeV LC with an integrated luminosity of 500 inverse fb is sufficient for distinguishing the three improved technicolor models experimentally.Comment: 7 pages, 6 figures, to appear in Physical Review