Oxygen-induced p(2x3) reconstruction on Mo(112) studied by LEED and STM

The open trough-and-row Mo(112) surface serves as substrate for the epitaxial growth of MoO2. In the early stage of oxygen exposure, oxygen chemisorption induces a p(2x3) surface reconstruction of the missing row type on Mo(112). The surface structure of this reconstructed surface has been studied in detail by low-energy electron diffraction and scanning tunneling microscope. The experimental findings can be explained based on the effective medium theory for oxygen adsorption on transition-metal surfaces, providing a structure model for the oxygen-modified Mo(112) surface. The structure model allows the discussion of the oxygen-chemisorbed surface phase as a possible precursor state fo

Novel TeV-scale seesaw mechanism with Dirac mediators

We propose novel tree level seesaw mechanism with TeV-scale vectorlike Dirac mediators that produce Majorana masses of the known neutrinos. The gauge quantum number assignment to the Dirac mediators allows them to belong to a weak triplet and a five-plet of nonzero hypercharge. The latter leads to new seesaw formula m_\nu ~ v^6/M^5, so that the empirical masses m_\nu ~ 10^{-1} eV can be achieved by M ~ TeV new states. There is a limited range of the parameter space with M < a few 100 GeV where the tree level contribution dominates over the respective loop contributions and the proposed mechanism is testable at the LHC. We discuss specific signatures for Dirac type heavy leptons produced by Drell-Yan fusion at the LHC.Comment: 10 pages, 1 figure, version corresponding to PL

Bounds on neutrino masses from leptogenesis in type-II see-saw models

The presence of the triplet $\Delta_{L}$ in left-right symmetric theories leads to type-II see-saw mechanism for the neutrino masses. In these models, assuming a normal mass hierarchy for the heavy Majorana neutrinos, we derive a lower bound on the mass of the lightest of heavy Majorana neutrino from the leptogenesis constraint. From this bound we establish a consistent picture for the hierarchy of heavy Majorana neutrinos in a class of left right symmetric models in which we identify the neutrino Dirac mass matrix with that of Fritzsch type charged lepton mass matrix. It is shown that these values are compatible with the current neutrino oscillation data.Comment: minor typos corrected, references added, match with published versio

Annihilating Leptogenesis

Leptogenesis is usually realized through decays of heavy particles. In this article we consider another possibility of generating a lepton asymmetry through annihilations of heavy particles. We demonstrate our idea with a realistic extension of the standard model containing a heavy doublet and a light singlet scalars in addition to right-handed neutrinos and Higgs triplets required for type-I+II seesaw of neutrino masses. We also clarify that this annihilating leptogenesis scenario can be naturally embedded in more fundamental theories, like left-right symmetric models or grand unified theories.Comment: 5 pages, 2 figures. A singlet scalar as dark matter is introduced to solve the flaw of the overabundant relic density in the original model. References added, typos corrected and title changed. Accepted by PL

Particle Production in Au+Au Collisions at sNN\sqrt{s_{NN}} = 9.2 GeV

In this report we present the first test run results from Au+Au collisions at $\sqrt{s_{NN}}$ = 9.2 GeV at RHIC. The large acceptance STAR detector has collected ~3k minimum bias collisions during this test run. The azimuthal anisotropy, identified particle spectra, particle ratios and HBT radii are observed to be consistent with the previous measurements from CERN SPS at similar center of mass energies. These results from the lowest collision energy at RHIC demonstrate the STAR detector's readiness to collect high quality data for the proposed Critical Point Search Program which allows us to explore the QCD phase diagram.Comment: 9 pages, 6 figures, Proceedings of 5th International Workshop on Critical Point and Onset of Deconfinemen

Leptogenesis Bound on Spontaneous Symmetry Breaking of Global Lepton Number

We propose a new class of leptogenesis bounds on the spontaneous symmetry breaking of global lepton number. These models have a generic feature of inducing new lepton number violating interactions, due to the presence of the Majorons. We analyzed the singlet Majoron model with right-handed neutrinos and find that the lepton number should be broken above 10^5 GeV to realize a successful leptogenesis because the annihilations of the right-handed neutrinos into the massless Majorons and into the standard model Higgs should go out of equilibrium before the sphaleron process is over. We then argue that this type of leptogenesis constraint should exist in the singlet-triplet Majoron models as well as in a class of R-parity violating supersymmetric Majoron models.Comment: 4 pages, 2 figure

Flavor Democracy and Type-II Seesaw Realization of Bilarge Neutrino Mixing

We generalize the democratic neutrino mixing Ansatz by incorporating the type-II seesaw mechanism with S(3) flavor symmetry. We find that bilarge neutrino mixing can naturally appear if the flavor democracy contribution is strongly suppressed due to significant cancellation between the conventional seesaw and triplet mass terms. Explicit S(3) symmetry breaking yields successful neutrino phenomenology and various testable correlations between the neutrino mass and mixing parameters. Among the results are a normal neutrino mass ordering, $0.005 \le |U_{e3}| \le 0.057$, $1 - \sin^2 2\theta_{23} \ge 0.005$, positive $J_{\rm CP}$ and moderate cancellation in the effective mass of the neutrinoless double beta decay.Comment: LaTex 12 pages (2 figures included). More discussions added. Accepted for publication in PL

Population III X-ray Binaries and their Impact on the Early Universe

The first population of X-ray binaries (XRBs) is expected to affect the thermal and ionization states of the gas in the early Universe. Although these X-ray sources are predicted to have important implications for high-redshift observable signals, such as the hydrogen 21-cm signal from cosmic dawn and the cosmic X-ray background, their properties are poorly explored, leaving theoretical models largely uninformed. In this paper we model a population of X-ray binaries arising from zero metallicity stars. We explore how their properties depend on the adopted initial mass function (IMF) of primordial stars, finding a strong effect on their number and X-ray production efficiency. We also present scaling relations between XRBs and their X-ray emission with the local star formation rate, which can be used in sub-grid models in numerical simulations to improve the X-ray feedback prescriptions. Specifically, we find that the uniformity and strength of the X-ray feedback in the intergalactic medium is strongly dependant on the IMF. Bottom-heavy IMFs result in a smoother distribution of XRBs, but have a luminosity orders of magnitude lower than more top-heavy IMFs. Top-heavy IMFs lead to more spatially uneven, albeit strong, X-ray emission. An intermediate IMF has a strong X-ray feedback while sustaining an even emission across the intergalactic medium. These differences in X-ray feedback could be probed in the future with measurements of the cosmic dawn 21-cm line of neutral hydrogen, which offers us a new way of constraining population III IMF.Comment: Accepted for publication in MNRAS, 17 pages, 9 figure