We analyze the lepton sector of a recently proposed nonsymmetric mass matrix model. Our model gives a unified description of quark and lepton with the same texture form based on an extended flavor $2\leftrightarrow 3$ symmetry with a phase. By investigating possible types of assignment for masses, we find that the model can lead to large lepton mixings which are consistent with experimental values. We also find that the model predicts a very small value, $1.3\times {10}^{-10}$, for the lepton mixing matrix element square $|U_{13}{|}^2$. The $CP$-violating phases in the lepton mixing matrix and a suppression of the averaged neutrino mass in the neutrinoless double beta decay also are predicted.

We present a precise calculation of the lightest neutral Higgs boson production associated with top-quark pair at a linear collider. The full one-loop electroweak $\mathcal{O}({\alpha }_{ew})$ contributions to the process $e^{+}{e}^{-}\to t\overline{t}{h}^0$ within the minimal supersymmetric standard model (MSSM) are included. We analyze the dependence of the electroweak corrections on the MSSM parameters such as $M_{A^0}$, $\tan \beta$, $M_2$ $A_f$, $M_{SUSY}$ and $\mu$. The results show that the full one-loop electroweak radiative corrections turn out to be about $-20\%$ quantitatively and thus are important for future $e^{+}{e}^{-}$ linear colliders.

The most general, renormalizable Lagrangian that includes massive neutrinos contains “right-handed neutrino” Majorana masses of order $M$. While there are prejudices in favor of $M\gg M_{\mathrm{weak}}$, virtually nothing is known about the magnitude of $M$. I argue that the Liquid Scintillator Neutrino Detector (LSND) anomaly provides, currently, the only experimental hint: $M\sim 1\mathrm{eV}$. If this is the case, the LSND mixing angles are functions of the active neutrino masses and mixing and, remarkably, adequate fits to all data can be naturally obtained. I also discuss consequences of this “eV-seesaw” for supernova neutrino oscillations, tritium beta-decay, neutrinoless double-beta-decay, and cosmology.

We present results on the production of direct photons, ${\pi }^0$, and $\eta$ mesons on nuclear targets at large transverse momenta ($p_T$). The data are from 530 and $800\mathrm{GeV}/c$ proton beams and $515\mathrm{GeV}/c$ ${\pi }^{-}$ beams incident upon copper and beryllium targets that span the kinematic range of $1.0<p_T\lesssim 10\mathrm{GeV}/c$ at central rapidities.

We propose that the $Y(4260)$ particle recently announced by BABAR is the first orbital excitation of a diquark-antidiquark state $([cs][\overline{c}\overline{s}])$. Using parameters recently determined to describe the $X(3872)$ and $X(3940)$ we show that the $Y$ mass is compatible with the orbital excitation picture. A crucial prediction is that $Y(4260)$ should decay predominantly in $D_s{\overline{D}}_s$. The $Y(4260)$ should also be seen in $B$ nonleptonic decays in association with one kaon. We consider the full nonet of related four-quark states and their predicted properties. Finally, we comment on a possible narrow resonance in the same channel.

In the most general two-Higgs-doublet model (2HDM), unitary transformations between the two Higgs fields do not change the functional form of the Lagrangian. All physical observables of the model must therefore be independent of such transformations (i.e., independent of the Lagrangian basis choice for the Higgs fields). We exhibit a set of basis-independent quantities that determine all tree-level Higgs couplings and masses. Some examples of the basis-independent treatment of 2HDM discrete symmetries are presented. We also note that the ratio of the neutral Higgs field vacuum expectation values, $\tan \beta$, is not a meaningful parameter in general, as it is basis dependent. Implications for the more specialized 2HDMs (e.g., the Higgs sector of the minimal supersymmetric extension of the standard model and the so-called type-I and type-II 2HDMs) are explored.

A recent paper by Lucas-Serrano et al. [A. Lucas-Serrano, J. A. Font, J. M. Ibánez, and J. M. Martí, Astron. Astrophys. 428, 703 (2004)] indicates that a high-resolution central (HRC) scheme is robust enough to yield accurate hydrodynamical simulations of special relativistic flows in the presence of ultrarelativistic speeds and strong shock waves. In this paper we apply this scheme in full general relativity (involving dynamical spacetimes), and assess its suitability by performing test simulations for oscillations of rapidly rotating neutron stars and merger of binary neutron stars. It is demonstrated that this HRC scheme can yield results as accurate as those by the so-called high-resolution shock-capturing (HRSC) schemes based upon Riemann solvers. Furthermore, the adopted HRC scheme has increased computational efficiency as it avoids the costly solution of Riemann problems and has practical advantages in the modeling of neutron star spacetimes. Namely, it allows simulations with stiff equations of state by successfully dealing with very low-density unphysical atmospheres. These facts not only suggest that such a HRC scheme may be a desirable tool for hydrodynamical simulations in general relativity, but also open the possibility to perform accurate magnetohydrodynamical simulations in curved dynamic spacetimes.

In this paper, we study phase transitions in asymmetrical fermion superfluids. In this scenario, the candidates to form a pair are particles with mismatched masses and chemical potentials. We derive an expression for the critical temperature in terms of the gap and masses (or chemical potentials) when the constraint of equal Fermi surfaces $m_a{\mu }_a=m_b{\mu }_b$ is imposed.

We consider a model with global Abelian chiral symmetry of two massless fermion fields interacting with a complex massive scalar field. We argue that the Schwinger-Dyson equations for the fermion and boson propagators admit ultraviolet-finite chiral-symmetry-breaking solutions provided the Yukawa couplings are large enough. The fermions acquire masses and the elementary excitations of the complex scalar field are the two real spin-zero particles with different masses. As a necessary consequence of the dynamical chiral symmetry breakdown both in the fermion and scalar sectors, one massless pseudoscalar Nambu-Goldstone boson appears in the spectrum as a collective excitation of both the fermion and the boson fields. Its effective couplings to the fermion and boson fields are calculable.

The Gross-Perry-Sorkin spacetime, formed by the Euclidean Taub-Newman-Unti-Tamburino space with the time trivially added, is the appropriate background of the Dirac magnetic monopole without an explicit mass term. We show that there exists a very simple five-dimensional metric of spacetimes carrying massive magnetic monopoles that is an exact solution of the vacuum Einstein equations. Moreover, the same isometry properties as the original Euclidean Taub-Newman-Unti-Tamburino space are preserved. This leads to an Abelian Kaluza-Klein theory whose metric appears as a combination between the Gross-Perry-Sorkin and Schwarzschild ones. The asymptotic motion of the scalar charged test particles is discussed, now by accounting for the mixing between the gravitational and magnetic effects.

We derive exact magnetically charged, static, and spherically symmetric black hole solutions of the four-dimensional Einstein-Born-Infeld-dilaton gravity. These solutions are neither asymptotically flat nor (anti)-de Sitter. The properties of the solutions are discussed. It is shown that the black holes are stable against linear radial perturbations.

We present a realistic dark energy model derived from particle physics. Our model has no free parameters and has an equivalent fit to the observational data (CMB, SN1a and LSS) as cosmological constant model (LCDM) and a better fit than the best effective $w(z)$ model. The only free parameter is the number of extra particles, besides the particles in the standard model and our dark energy model, contained in the Universe. With the lack of a clear determination of the cosmological parameters theoretical considerations should be taken seriously to distinguish between dark energy models.

It has been widely claimed that inflation is generically eternal to the future, even in models where the inflaton potential monotonically increases away from its minimum. The idea is that quantum fluctuations allow the field to jump uphill, thereby continually revitalizing the inflationary process in some regions. In this paper we investigate a simple model of this process, pertaining to $\lambda {\varphi }^4$ inflation, in which analytic progress may be made. We calculate several quantities of interest, such as the expected number of inflationary efolds, first without and then with various selection effects. With no additional weighting, the stochastic noise has little impact on the total number of inflationary efoldings in the model even if the inflaton starts with a Planckian energy density. A “rolling” volume factor, i.e. weighting in proportion to the volume at that time, also leads to a monotonically decreasing Hubble constant and hence no eternal inflation. We show how stronger selection effects including a constraint on the initial and final states and weighting with the final volume factor can lead to a picture similar to that usually associated with eternal inflation.

By simulating a uniform electric field on a lattice and measuring the change in the rest mass, we calculate the electric polarizability of neutral mesons and baryons using the methods of quenched lattice QCD. Specifically, we measure the electric polarizability coefficient from the quadratic response to the electric field for 10 particles: the vector mesons ${\rho }^0$ and $K^{*0}$; the octet baryons n, ${\Sigma }^0$, ${\Lambda }^0$, and ${\Xi }^0$; and the decuplet baryons ${\Delta }^0$, ${\Sigma }^{*0}$, and ${\Xi }^{*0}$. Independent calculations using two fermion actions were done for consistency and comparison purposes. One calculation uses Wilson fermions with a lattice spacing of $a=0.10$ fm. The other uses tadpole-improved Lüscher-Weisz gauge fields and clover quark action with a lattice spacing $a=0.17$ fm. Our results for neutron electric polarizability are compared to experiment.

A study of the finite-size effect is carried out for spectra of both ground-state and excited-state baryons in quenched lattice QCD using Wilson fermions. Our simulations are performed at $\beta =6/g^2=6.2$ with three different spatial sizes, $La\sim$ 1.6, 2.2 and 3.2 fm. It is found that the physical lattice size larger than 3 fm is required for $\Delta$ states in all spin-parity ($J^P=1/2^{\pm },3/2^{\pm }$) channels and also negative-parity nucleon ($N^{*}$) state ($J^P=1/2^{-}$) even in the rather heavy quark mass region ($M_{\pi }\sim 1.0\mathrm{GeV}$). We also find a peculiar behavior of the finite-size effect on the hyperfine mass splittings between the nucleon and the $\Delta$ in both parity channels.

We study a spin-1 single-flavor color-superconducting phase which results from a color-spin locking (CSL) interaction in two-flavor quark matter. This phase is particularly interesting for compact star cooling applications since the CSL phase may survive under charge neutrality constraints implying a mismatch between up- and down-quark chemical potentials which can destroy the scalar diquark condensate. CSL gaps are evaluated within an NJL model and they are found to be consistent with cooling phenomenology if a density dependent coupling constant is used.

Quark and gluon parton dihadron fragmentation functions and their evolution are studied in the process of $e^{+}{e}^{-}$ annihilation. We provide definitions of such dihadron fragmentation functions in terms of parton matrix elements and derive the momentum sum rules and their connection to single hadron fragmentation functions. We parametrize results from the Lund Monte Carlo model JETSET as the initial conditions for the parton dihadron fragmentation functions at the scale $Q_0^2=2{\mathrm{GeV}}^2$. The evolution equations for the quark and gluon fragmentation functions are solved numerically and the results at different higher scales $Q^2$ agree well with JETSET results. The importance of the input from the single fragmentation functions is pointed out.

We derive mass formulas for the ground state, $J^P=0^{-}$ and $1^{-}$, and first excited even-parity, $J^P=0^{+}$ and $1^{+}$, charmed mesons including one-loop chiral corrections and $O(1/m_c)$ counterterms in heavy hadron chiral perturbation theory. We show that including these counterterms is critical for fitting the current data. We find that certain parameter relations in the parity doubling model are not renormalized at one-loop, providing a natural explanation for the observed equality of the hyperfine splittings of ground state and excited doublets.

The leading order contribution to the direct $CP$ asymmetry in ${\tau }^{\pm }\to K^{\pm }{\pi }^0{\nu }_{\tau }$ decay rates is evaluated within the standard model. The weak phase required for $CP$ violation is introduced through an interesting mechanism involving second order weak interactions, which is also responsible for tiny violations of the $\Delta S=\Delta Q$ rule in $K_{l3}$ decays. The calculated $CP$ asymmetry turns out to be of order ${10}^{-12}$, leaving a large window for studying effects of nonstandard sources of $CP$ violation in this observable.