We present a determination of the QCD parameter $\Lambda$ in the quenched approximation ($n_f=0$) and for two flavors ($n_f=2$) of light dynamical quarks. The calculations are performed on the lattice using $O(a)$ improved Wilson fermions and include taking the continuum limit. We find ${\Lambda }_{n_f=0}^{\overline{MS}}=259(1)(19)\mathrm{MeV}$ and ${\Lambda }_{n_f=2}^{\overline{MS}}=261(17)(26)\mathrm{MeV}$, using $r_0=0.467\mathrm{fm}$ to set the scale. Extrapolating our results to five flavors, we obtain for the running coupling constant at the mass of the $Z$ boson ${\alpha }_s^{\overline{MS}}(m_Z)=0.112(1)(2)$.

We investigate recently proposed ${\mathrm{HP}}^1$ $\sigma$-model embedding method aimed to study the topology of SU(2) gauge fields. The ${\mathrm{HP}}^1$ based topological charge is shown to be fairly compatible with various known definitions. We study the corresponding topological susceptibility and estimate its value in the continuum limit. The geometrical clarity of ${\mathrm{HP}}^1$ approach allows to investigate nonperturbative aspects of SU(2) gauge theory on a qualitatively new level. In particular, we obtain a numerically precise estimation of gluon condensate and its leading quadratic correction. Furthermore, we present clear evidences that the string tension is to be associated with global (percolating) regions of sign-coherent topological charge. As a by-product of our analysis we estimate the continuum value of quenched chiral condensate and the dimensionality of regions, which localize the lowest eigenmodes of overlap Dirac operator.

Recently BES collaboration observed one interesting resonance X(1835). We point out that its mass, total width, production rate, and decay pattern favor its assignment as the second radial excitation of ${\eta }^{\prime }$ meson very naturally.

We report on a method for matching the next-to-leading order calculation of QCD jet production in $e^{+}{e}^{-}$ annihilation with a Monte Carlo parton shower event generator (MC) to produce realistic final states. The final result is accurate to next-to-leading order (NLO) for infrared-safe one-scale quantities, such as the Durham 3-jet fraction $y_3$, and agrees well with parton shower results for multiscale quantities, such as the jet mass distribution in 3-jet events. For our numerical results, the NLO calculation is matched to the event generator Pythia, though the method is more general. We compare one-scale and multiscale quantities from pure NLO, pure MC, and matched NLO-MC calculations.

The Sivers function is extracted from HERMES data on single spin asymmetries in semi-inclusive deeply inelastic scattering. Our analysis use a simple Gaussian model for the distribution of transverse parton momenta, together with the flavor dependence given by the leading $1/N_c$ approximation and a neglect of the Sivers antiquark distribution. We find that within the errors of the data these approximations are sufficient.

Koide’s mass relation of charged leptons has been extended to quarks and neutrinos, and we prove here that this relation is independent of energy scale in a huge energy range from 1 GeV to $2\times {10}^{16}\mathrm{GeV}$. By using the parameters $k_u$, $k_d$, and $k_{\nu }$ to describe the deviations of quarks and neutrinos from the exact Koide’s relation, we also check the quark-lepton complementarity of masses such as $k_l+k_d\approx k_{\nu }+k_u\approx 2$, and show that it is also independent (or insensitive) of energy scale.

We present a simultaneous measurement of the ${\overline{B}}^0$ lifetime ${\tau }_{B^0}$ and $B^0{\overline{B}}^0$ oscillation frequency $\Delta m_d$. We use a sample of about 50 000 partially reconstructed ${\overline{B}}^0\to D^{*+}{\ell }^{-}{\overline{\nu }}_{\ell }$ decays identified with the BABAR detector at the PEP-II $e^{+}{e}^{-}$ storage ring at SLAC. The flavor of the other $B$ meson in the event is determined from the charge of another high-momentum lepton. The results are ${\tau }_{B^0}=(1.504\pm 0.013{(\mathrm{stat})}_{-0.013}^{+0.018}(\mathrm{syst}))\mathrm{ps}$, $\Delta m_d=(0.511\pm 0.007{(\mathrm{stat})}_{-0.006}^{+0.007}{(\mathrm{syst}))\mathrm{ps}}^{-1}$.

In this work we investigate two distinct extensions of the deformation procedure introduced in former works on deformed defects. The first extension deals with the use of deformation functions which can assume complex values, and the second concerns the possibility of making the deformation dependent on the defect solution of the model used to implement the deformation. These two extensions bring the deformation procedure to a significantly higher standard and allow to build interesting results, as we explicitly illustrate with examples of current interest to high energy physics.

We consider the asymptotic quasinormal frequencies of various spin fields in Schwarzschild and Reissner-Nordström black holes. In the Schwarzschild case, the real part of the asymptotic frequency is $\ln 3$ for the spin 0 and the spin 2 fields, while for the spin $1/2$, the spin 1, and the spin $3/2$ fields it is zero. For the nonextreme charged black holes, the spin $3/2$ Rarita-Schwinger field has the same asymptotic frequency as that of the integral spin fields. However, the asymptotic frequency of the Dirac field is different, and its real part is zero. For the extremal case, which is relevant to the supersymmetric consideration, all the spin fields have the same asymptotic frequency, the real part of which is zero. For the imaginary parts of the asymptotic frequencies, it is interesting to see that it has a universal spacing of $1/4M$ for all the spin fields in the single-horizon cases of the Schwarzschild and the extreme Reissner-Nordström black holes. The implications of these results to the universality of the asymptotic quasinormal frequencies are discussed.

Modified theories of gravity have recently been studied by several authors as possibly viable alternatives to the cosmological concordance model. Such theories attempt to explain the accelerating expansion of the universe by changing the theory of gravity, instead of introducing dark energy. In particular, a class of models based on higher order curvature invariants, so-called $f(R)$ gravity models, has drawn attention. In this letter we show that within this framework, the expansion history of the universe does not uniquely determine the form of the gravitational action and it can be radically different from the standard Einstein-Hilbert action. We demonstrate that for any fluid with a barotropic equation state, there always exists a class of $f(R)$ models that will have exactly the same expansion history as that arising from the Einstein-Hilbert action. This also holds for multicomponent systems that allow an effective fluid description. Consequently, any $f(R)$ model that leads to a given expansion history can always be generalized to a class of models that have exactly the same expansion history as a solution. We explicitly show how one can extend the Einstein-Hilbert action by constructing a $f(R)$ theory that is equivalent on the classical level. As a result, we find that one cannot mimic $\Lambda \mathrm{CDM}$ type expansion exactly by a matter only universe by any choice of $f(R)$ without introducing an explicit cosmological constant. Because of the classical equivalence between $f(R)$ theories and Einstein-Hilbert gravity with an extra scalar field, one can also hence construct equivalent scalar-tensor theories with standard expansion.

Baryon and lepton numbers of the Universe in leptogenesis with Dirac neutrino and leptogenesis with Majorana neutrino scenarios are considered. It is shown that despite quite different features of Dirac and Majorana fermions both scenarios yield the same relation among the initial lepton and the final baryon asymmetries. Moreover right-handed neutrinos in the leptogenesis with Dirac neutrino scenario have very little impact on the effective number of relativistic degrees of freedom, constrained by BBN. Thus the two scenarios are similar from the cosmological point of view. It is also pointed out that in thermal equilibrium the $3B+L$ sum is zero for left-handed fermions.

The curl modes of cosmic microwave background polarization allow one to indirectly constrain the primordial background of gravitational waves with frequencies around ${10}^{-18}$ to ${10}^{-16}\mathrm{Hz}$. The proposed high precision timing observations of a large sample of millisecond pulsars with the pulsar timing array or with the square kilometer array can either detect or constrain the stochastic gravitational-wave background at frequencies greater than roughly $0.1{\mathrm{\text{yr}}}^{-1}$. While existing techniques are limited to either observe or constrain the gravitational-wave background across six or more orders of magnitude between ${10}^{-16}$ and ${10}^{-10}\mathrm{Hz}$, we suggest that the anisotropy pattern of time variation of the redshift related to a sample of high-redshift objects can be used to study the background around a frequency of ${10}^{-12}\mathrm{Hz}$. Useful observations to detect an anisotropy signal in the global redshift change include spectroscopic observations of the $\mathrm{Ly}\mathrm{\text{−}}\alpha$ forest in absorption towards a sample of quasars, redshifted 21 cm line observations either in absorption or emission towards a sample of neutral HI regions before or during reionization, and high-frequency (0.1 to 1 Hz) gravitational-wave analysis of a sample of neutron star–neutron star binaries detected with gravitational-wave instruments such as the Decihertz Interferometer Gravitational Wave Observatory (DECIGO). For reasonable observations expected in the future involving extragalactic sources, we find limits at the level of ${\Omega }_{\mathrm{GW}}<{10}^{-6}$ at a frequency around ${10}^{-12}\mathrm{Hz}$ while the ultimate limit is likely to be around ${\Omega }_{\mathrm{GW}}<{10}^{-11}$. On the other hand, if there is a background of gravitational waves at ${10}^{-12}\mathrm{Hz}$ with an amplitude larger than this limit, its presence will be visible as a measurable anisotropy in the time-evolving redshift of extragalactic sources.

We study lepton flavor violation (LFV) associated with tau leptons in the framework of the two Higgs doublet model, in which LFV couplings are introduced as a deviation from Model II Yukawa interaction. Parameters of the model are constrained from experimental results and also from requirements of theoretical consistencies such as vacuum stability and perturbative unitarity. Current data for rare tau decays provide substantial upper limits on the LFV Yukawa couplings in the large $\tan \beta$ region ($\tan \beta \gtrsim 30$), which are comparable with predictions in fundamental theories. Here $\tan \beta$ is the ratio of vacuum expectation values of the two Higgs doublets. We show that a search for the LFV decays ${\varphi }^0\to {\tau }^{\pm }{\mu }^{\mp }$ $({\tau }^{\pm }{e}^{\mp })$ of neutral Higgs bosons (${\varphi }^0=h,H$ and $A$) at future collider experiments can be useful to further constrain the LFV couplings especially in the relatively small $\tan \beta$ region ($\tan \beta \lesssim 30$), where rare tau decay data cannot give any strong limit.

We take a critical view of the treatment of threshold effects in SUSY spectrum computations from high-scale input. We discuss the two principal methods of (a) renormalization at a common SUSY scale versus (b) integrating out sparticles at their own mass scales. We point out problems in the implementations in public spectrum codes, together with suggestions for improvements. In concrete examples, we compare results of Isajet 7.72 and SPheno 2.2.3, and present the improvements done in Isajet 7.73. We also comment on theoretical uncertainties. Last but not least, we outline how a consistent multiscale approach may be achieved.

The high energy and large $p_T$ inclusive polarized process, $(A,S_A)+(B,S_B)\to C+X$, is considered under the assumption of a generalized QCD factorization scheme. For the first time all transverse motions, of partons in hadrons and of hadrons in fragmenting partons, are explicitly taken into account; the elementary interactions are computed at leading order with noncollinear exact kinematics, which introduces many phases in the expressions of their helicity amplitudes. Several new spin and ${\mathit{k}}_{\perp }$ dependent soft functions appear and contribute to the cross sections and to spin asymmetries; we put emphasis on their partonic interpretation, in terms of quark and gluon polarizations inside polarized hadrons. Connections with other notations and further information are given in some Appendixes. The formal expressions for single and double spin asymmetries are derived. The transverse single spin asymmetry $A_N$, for $p^{\uparrow }p\to \pi X$ processes is considered in more detail, and all contributions are evaluated numerically by saturating unknown functions with their upper positivity bounds. It is shown that the integration of the phases arising from the noncollinear kinematics strongly suppresses most contributions to the single spin asymmetry, leaving at work predominantly the Sivers effect and, to a lesser extent, the Collins mechanism.

We investigate three-color QCD thermodynamics at finite quark chemical potential. Lattice QCD results are compared with a generalized Nambu Jona-Lasinio model in which quarks couple simultaneously to the chiral condensate and to a background temporal gauge field representing Polyakov loop dynamics. This so-called PNJL model thus includes features of both deconfinement and chiral symmetry restoration. The parameters of the Polyakov loop effective potential are fixed in the pure-gauge sector. The chiral condensate and the Polyakov loop as functions of temperature and quark chemical potential are calculated by minimizing the thermodynamic potential of the system. The resulting equation of state, (scaled) pressure difference and quark number density at finite quark chemical potential are then confronted with corresponding Lattice QCD data.

Using the color-magnetic interaction Hamiltonian with SU(3) flavor symmetry breaking, we perform a schematic study of the masses of the $J^P=1^{+}$ tetraquarks in the antidecuplet representation. After diagonalizing the mass matrix, we find the $ud\overline{s}\overline{s}$ tetraquark could lie as low as about 1350 MeV. It decays into $K^{+}{K}^0{\pi }^0$, $K^{+}{K}^{+}{\pi }^{-}$, $K^0{K}^0{\pi }^{+}$ via $P$-wave. The dual suppression from the not-so-big three-body phase space and $P$-wave decay barrier may render this exotic state rather narrow. Future experimental exclusion of this state will cast doubt on the validity of applying the simple color-magnetic Hamiltonian to the multiquark system.

A phenomenological approach for the universal mass matrix model with a broken flavor $2\leftrightarrow 3$ symmetry is explored by introducing the $2\leftrightarrow 3$ antisymmetric parts of mass matrices for quarks and charged leptons. We present explicit texture components of the mass matrices, which are consistent with all the neutrino oscillation experiments and quark mixing data. The mass matrices have a common structure for quarks and leptons, while the large lepton mixings and the small quark mixings are derived with no fine-tuning due to the difference of the phase factors. The model predicts a value $2.4\times {10}^{-3}$ for the lepton mixing matrix element square $|U_{13}{|}^2$, and also $⟨m_{\nu }⟩=(0.89-1.4)\times {10}^{-4}\mathrm{eV}$ for the averaged neutrino mass which appears in the neutrinoless double beta decay.

If the $X(3872)$ is a loosely-bound $D^{*0}{\overline{D}}^0/D^0{\overline{D}}^{*0}$ molecule, its inclusive production rate can be described by the NRQCD factorization formalism that applies to inclusive quarkonium production. We argue that if the molecule has quantum numbers $J^{PC}=1^{++}$, the most important term in the factorization formula should be the color-octet ${}^{3}S_1$ term. This is also one of the two most important terms in the factorization formulas for ${\chi }_{cJ}$. Since the color-octet ${}^{3}S_1$ term dominates ${\chi }_{cJ}$ production for many processes, the ratio of the inclusive direct production rates for $X$ and ${\chi }_{cJ}$ should be roughly the same for these processes. The assumption that the ratio of the production rates for $X$ and ${\chi }_{cJ}$ is the same for all processes is used to estimate the inclusive production rate of $X$ in $B$ meson decays, $Z^0$ decays, and in $p\overline{p}$ collisions.

Zero modes of the world-sheet spinors of a closed string can source higher order moments of the bulk supergravity fields. In this work, we analyze various configurations of closed strings focusing on the imprints of the quantized spinor vacuum expectation values onto the tails of bulk fields. We identify supersymmetric arrangements for which all multipole charges vanish; while for others, we find that one is left with Neveu-Schwarz–Neveu-Schwarz, and Ramond-Ramond dipole and quadrupole moments. Our analysis is exhaustive with respect to all the bosonic fields of the bulk and to all higher order moments. We comment on the relevance of these results to entropy computations of hairy black holes of a single charge or more, and to open/closed string duality.