We present a search for the decays $B^0\to e^{+}{e}^{-}$, $B^0\to {\mu }^{+}{\mu }^{-}$, and $B^0\to e^{\pm }{\mu }^{\mp }$ using data collected with the BABAR detector at the PEP-II $e^{+}{e}^{-}$ collider at SLAC. Using a data set corresponding to $384\times {10}^6$ $B\overline{B}$ pairs, we do not find evidence of any of the three decay modes. We obtain upper limit on the branching fractions, at 90% confidence level, of $\mathcal{B}(B^0\to e^{+}{e}^{-})<11.3\times {10}^{-8}$, $\mathcal{B}(B^0\to {\mu }^{+}{\mu }^{-})<5.2\times {10}^{-8}$, and $\mathcal{B}(B^0\to e^{\pm }{\mu }^{\mp })<9.2\times {10}^{-8}$.

In 2006 the PVLAS collaboration reported the observation of an optical rotation generated in vacuum by a magnetic field. To further check against possible instrumental artifacts, several upgrades to the PVLAS apparatus have been made during the past year. Two data taking runs, at the wavelength of 1064 nm, have been performed in the new configuration with magnetic field strengths of 2.3 and 5 T. The 2.3 T field value was chosen in order to avoid stray fields. The new observations do not show the presence of a rotation signal down to the levels of $1.2\times {10}^{-8}\mathrm{rad}$ at 5 T and $1.0\times {10}^{-8}\mathrm{rad}$ at 2.3 T (at 95% C.L.) with 45 000 passes in the magnetic field zone. In the same conditions no ellipticity signal was detected down to $1.4\times {10}^{-8}$ at 2.3 T (at 95% C.L.), whereas at 5 T a signal is still present. The physical nature of this ellipticity as due to an effect depending on $B^2$ can be excluded by the measurement at 2.3 T. These new results completely exclude the previously published magnetically induced vacuum dichroism results, indicating that they were instrumental artifacts. These new results therefore also exclude the particle interpretation of the previous PVLAS results as due to a spin-zero boson. The background ellipticity at 2.3 T can be used to determine a new limit on the total photon-photon scattering cross section of ${\sigma }_{\gamma \gamma }<4.5\times {10}^{-34}\mathrm{barn}$ at 95% C.L.

We show that the spin connection of the standard metric on a six-dimensional sphere gives an exact solution to the generalized self-duality equations suggested by Tchrakian some years ago. We work on a SO(6) gauge theory with a higher-derivative coupling term. The model consists of vector fields only. The pseudoenergy is bounded from below by a topological charge, which is proportional to the winding number of spatial $S^5$ around the internal space SO(6). The fifth homotopy group of SO(6) is, indeed, $\mathbb{Z}$. The coupling constant of the higher derivative term is quadratic in the radius of the underlying space $S^6$.

We quantize the set of all quarter Bogomol’nyi-Prasad-Sommerfield (BPS) brane probe solutions in global ${\mathrm{AdS}}_3\times S^3\times T^4/K3$ found in G. Mandal, S. Raju, and M. Smedback, preceding article, Phys. Rev. D 77, 046011 (2008).. We show that, generically, these solutions give rise to states in discrete representations of the $SL(2,R)$ Wess-Zumino-Witten model on ${\mathrm{AdS}}_3$. Our procedure provides us with a detailed description of the low energy $\frac{1}{4}$ and $\frac{1}{2}$ BPS sectors of string theory on this background. The $\frac{1}{4}$ BPS partition function jumps as we move off the point in moduli space where the bulk theta angle and Neveu-Schwarz fields vanish. We show that generic $\frac{1}{2}$ BPS states are protected because they correspond to geodesics rather than puffed up branes. By exactly quantizing the simplest of the probes above, we verify our description of $\frac{1}{4}$ BPS states and find agreement with the known spectrum of $\frac{1}{2}$ BPS states of the boundary theory. We also consider the contribution of these probes to the elliptic genus and discuss puzzles, and their possible resolutions, in reproducing the elliptic genus of the symmetric product.

We parametrize all classical probe brane configurations that preserve four supersymmetries in (a) the extremal D1-D5 geometry, (b) the extremal D1-D5-P geometry, (c) the smooth D1-D5 solutions proposed by Lunin and Mathur, and (d) global ${\mathrm{AdS}}_3\times S_3\times T^4/K3$. These configurations consist of D1 branes, D5 branes, and bound states of D5 and D1 branes with the property that a particular Killing vector is tangent to the brane world volume at each point. We show that the supersymmetric sector of the D5-brane world volume theory may be analyzed in an effective $1+1$ dimensional framework that places it on the same footing as D1 branes. In global AdS and the corresponding Lunin-Mathur solution, the solutions we describe are “bound” to the center of AdS for generic parameters and cannot escape to infinity. We show that these probes only exist on the submanifold of moduli space where the background $B_{NS}$ field and theta angle vanish. We quantize these probes in the near-horizon region of the extremal D1-D5 geometry and obtain the theory of long strings discussed by Seiberg and Witten.

We present a simple mechanism by which supersymmetry can be dynamically broken in intersecting brane models, naturally generating an exponentially small scale. Rather than utilize either non-Abelian gauge dynamics or $D$-instantons, our mechanism uses world sheet instantons to generate the small scale in a hidden sector.

We study the properties of massless and massive quarks coupled with a scalar and pseudoscalar boson at finite temperature in Yukawa models at the one-loop order. The behavior of the spectral function and the pole structure of the propagator are analyzed as functions of temperature $T$ and the quark mass $m_f$. It is shown that the three-peak structure of the spectral function found in a previous work for massless quarks is formed at temperatures comparable to the boson mass even for finite $m_f$, but gradually ceases to exist as $m_f$ becomes larger. We identify the three poles of the quark propagator corresponding to the collective excitations of the quark in the complex-energy plane. It is shown that the three trajectories made by the poles along with a variation of $T$ undergo a structural rearrangement at a critical quark mass when $m_f$ is increased. This suggests that the physics content of the collective quark excitations is changed in a drastic way at this point. The results are nicely accounted for with the notion of the level mixing induced by a resonant scattering of the massive boson with quarks and holes of thermally excited antiquarks.

In the paper we check whether the contribution of $(-)(1+z{)}^6$ type in the Friedmann equation can be tested. We consider some astronomical tests to constrain the density parameters in such models. We describe different interpretations of such an additional term: geometric effects of loop quantum cosmology, effects of braneworld cosmological models, nonstandard cosmological models in metric-affine gravity, and models with spinning fluid. Kinematical (or geometrical) tests based on null geodesics are insufficient to separate individual matter components when they behave like perfect fluid and scale in the same way. Still, it is possible to measure their overall effect. We use recent measurements of the coordinate distances from the Fanaroff-Riley type IIb radio galaxy data, supernovae type Ia data, baryon oscillation peak and cosmic microwave background radiation observations to obtain stronger bounds for the contribution of the type considered. We demonstrate that, while ${\rho }^2$ corrections are very small, they can be tested by astronomical observations—at least in principle. Bayesian criteria of model selection (the Bayesian factor, AIC, and BIC) are used to check if additional parameters are detectable in the present epoch. As it turns out, the $\Lambda \mathrm{CDM}$ model is favored over the bouncing model driven by loop quantum effects. Or, in other words, the bounds obtained from cosmography are very weak, and from the point of view of the present data this model is indistinguishable from the $\Lambda \mathrm{CDM}$ one.

Magnetic fields of intensities similar to those in our galaxy are also observed in high redshift galaxies, where a mean field dynamo would not have had time to produce them. Therefore, a primordial origin is indicated. It has been suggested that magnetic fields were created at various primordial eras: during inflation, the electroweak phase transition, the quark-hadron phase transition (QHPT), during the formation of the first objects, and during reionization. We suggest here that the large-scale fields $\sim \mu \mathrm{G}$, observed in galaxies at both high and low redshifts by Faraday rotation measurements (FRMs), have their origin in the electromagnetic fluctuations that naturally occurred in the dense hot plasma that existed just after the QHPT. We evolve the predicted fields to the present time. The size of the region containing a coherent magnetic field increased due to the fusion of smaller regions. Magnetic fields (MFs) $\sim 10\mu \mathrm{G}$ over a comoving $\sim 1\mathrm{pc}$ region are predicted at redshift $z\sim 10$. These fields are orders of magnitude greater than those predicted in previous scenarios for creating primordial magnetic fields. Line-of-sight average MFs $\sim {10}^{-2}\mu \mathrm{G}$, valid for FRMs, are obtained over a 1 Mpc comoving region at the redshift $z\sim 10$. In the collapse to a galaxy (comoving size $\sim 30\mathrm{kpc}$) at $z\sim 10$, the fields are amplified to $\sim 10\mu \mathrm{G}$. This indicates that the MFs created immediately after the QHPT (${10}^{-4}\mathrm{s}$), predicted by the fluctuation-dissipation theorem, could be the origin of the $\sim \mu \mathrm{G}$ fields observed by FRMs in galaxies at both high and low redshifts. Our predicted MFs are shown to be consistent with present observations. We discuss the possibility that the predicted MFs could cause non-negligible deflections of ultrahigh energy cosmic rays and help create the observed isotropic distribution of their incoming directions. We also discuss the importance of the volume average magnetic field predicted by our model in producing the first stars and in reionizing the Universe.

Flat directions are a generic feature of the scalar potential in supersymmetric gauge field theories. They can arise, for example, from $D$-terms associated with an extra Abelian gauge symmetry. Even when supersymmetry is broken softly, there often remain directions in the scalar field space along which the potential is almost flat. Upon breaking a gauge symmetry along one of these almost-flat directions, cosmic strings may form. Relative to the standard cosmic string picture based on the Abelian Higgs model, these flat-direction cosmic strings have the extreme type-I properties of a thin gauge core surrounded by a much wider scalar field profile. We perform a comprehensive study of the microscopic, macroscopic, and observational characteristics of this class of strings. We find many differences from the standard string scenario, including stable higher winding-mode strings, the dynamical formation of higher mode strings from lower ones, and a resultant multitension scaling string network in the early universe. These strings are only moderately constrained by current observations, and their gravitational wave signatures may be detectable at future gravity wave detectors. Furthermore, there is the interesting but speculative prospect that the decays of cosmic string loops in the early universe could be a source of ultrahigh-energy cosmic rays or nonthermal dark matter. We also compare the observational signatures of flat-direction cosmic strings with those of ordinary cosmic strings as well as $(p,q)$ cosmic strings motivated by superstring theory.

Measurements of standard candles and measurements of standard rulers give an inconsistent picture of the history of the universe. This discrepancy can be explained if photon number is not conserved as computations of the luminosity distance must be modified. I show that photon number is not conserved when photons mix with chameleons in the presence of a magnetic field. The strong magnetic fields in a supernova mean that the probability of a photon converting into a chameleon in the interior of the supernova is high, this results in a large flux of chameleons at the surface of the supernova. Chameleons and photons also mix as a result of the intergalactic magnetic field. These two effects combined cause the image of the supernova to be brightened resulting in a model which fits both observations of standard candles and observations of standard rulers.

We derive upper limits on the ratio $f_{\mathrm{GRB}/\mathrm{CCSN}}(z)\equiv R_{\mathrm{GRB}}(z)/R_{\mathrm{CCSN}}(z)\equiv f_{\mathrm{GRB}/\mathrm{CCSN}}(0)(1+z{)}^{\alpha }$, the ratio of the rate, $R_{\mathrm{GRB}}$, of long-duration gamma-ray bursts (GRBs) to the rate, $R_{\mathrm{CCSN}}$, of core-collapse supernovae (CCSNe) in the Universe ($z$ being the cosmological redshift and $\alpha \ge 0$), by using the upper limit on the diffuse TeV-PeV neutrino background given by the AMANDA-II experiment in the South Pole, under the assumption that GRBs are sources of TeV-PeV neutrinos produced from decay of charged pions produced in $p\gamma$ interaction of protons accelerated to ultrahigh energies at internal shocks within GRB jets. For the assumed “concordance model” of cosmic star formation rate, $R_{\mathrm{SF}}$, with $R_{\mathrm{CCSN}}(z)\propto R_{\mathrm{SF}}(z)$, our conservative upper limits are $f_{\mathrm{GRB}/\mathrm{CCSN}}(0)\le 5.0\times {10}^{-3}$ for $\alpha =0$, and $f_{\mathrm{GRB}/\mathrm{CCSN}}(0)\le 1.1\times {10}^{-3}$ for $\alpha =2$, for example. These limits are already comparable to (and, for $\alpha \ge 1$, already more restrictive than) the current upper limit on this ratio inferred from other astronomical considerations, thus providing a useful independent probe of and constraint on the CCSN-GRB connection. Nondetection of a diffuse TeV–PeV neutrino background by the upcoming IceCube detector in the South Pole after three years of operation, for example, will bring down the upper limit on $f_{\mathrm{GRB}/\mathrm{CCSN}}(0)$ to below a few $\times {10}^{-5}$ level, while a detection will confirm the hypothesis of proton acceleration to ultrahigh energies in GRBs and will potentially also yield the true rate of occurrence of these events in the Universe.

It is interesting to search for new physics beyond the standard model at Large Hadron Collider beauty (LHCb). We suggest that weak decays of doubly charmed baryon such as ${\Xi }_{cc}(3520{)}^{+}$, ${\Xi }_{cc}^{++}$ to charmless final states would be a possible signal for new physics. In this work we consider two models, i.e. the unparticle and $Z^{\prime }$ as examples to study such possibilities. We also discuss the cases for ${\Xi }_{bb}^0$, ${\Xi }_{bb}^{-}$ which have not been observed yet, but one can expect to find them when LHCb begins running. Our numerical results show that these two models cannot result in sufficiently large decay widths, therefore if such modes are observed at LHCb, there must be a new physics other than the unparticle or $Z^{\prime }$ models.

We study the effect of $b\to s\overline{s}s$ scalar/pseudoscalar operators in $B\to K{\eta }^{(\prime )}$, $\varphi K^{*}$ decays. In the minimal supersymmetric standard model (MSSM), such scalar/pseudoscalar operators can be induced by the penguin diagrams of neutral-Higgs bosons. These operators can be Fierz-transformed into tensor operators, and the resultant tensor operators could affect the transverse polarization amplitudes in $B\to \varphi K^{*}$ decays. A combined analysis of the decays $B\to \varphi K^{*}$ and $B\to K{\eta }^{(\prime )}$, including $b\to s\overline{s}s$ scalar/pseudoscalar operators and their Fierz-transformed tensor operators originated from the MSSM, is performed. Our study is based on the following: (1) Assuming that weak annihilations in $B\to \varphi K^{*}$ are negligible and the polarization puzzle is resolved by Fierz-transformed tensor operators, it results in too large coefficients of scalar/pseudoscalar operators, such that the resulting $B\to K{\eta }^{(\prime )}$ branching fractions are much larger than observations. (2) When we take the weak annihilations in $B\to \varphi K^{*}$ into account, the polarization puzzle can be resolved. In this case, new physics effects are strongly suppressed and no more relevant to the enhancement of the transverse modes in $B\to \varphi K^{*}$ decays.

Based on the main assumption that the $D_{sJ}(2860)$ belongs to the $2^3{P}_0$ $q\overline{q}$ multiplet, the masses of the scalar meson nonet are estimated in the framework of the relativistic independent quark model, Regge phenomenology, and meson-meson mixing. We suggest that the $a_0(1005)$, $K_0{}^{*}(1062)$, $f_0(1103)$, and $f_0(564)$ constitute the ground scalar meson nonet; it is supposed that these states would likely correspond to the observed states $a_0(980)$, $\kappa (900)$, $f_0(980)$, and $f_0(600)/\sigma$, respectively. Also $a_0(1516)$, $K_0{}^{*}(1669)$, $f_0(1788)$, and $f_0(1284)$ constitute the first radial scalar meson nonet, it is supposed that these states would likely correspond to the observed states $a_0(1450)$, $K_0{}^{*}(1430)$, $f_0(1710)$, and $f_0(1370)$, respectively. The scalar state $f_0(1500)$ may be a good candidate for the ground scalar glueball. The agreement between the present findings and those given by other different approaches is satisfactory.

We report measurements of $B$-meson decays into two- and three-body final states containing two charmed baryons using a sample of $230\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ decays. We find significant signals in two modes, measuring branching fractions $\mathcal{B}(B^{-}\to {\Lambda }_c^{+}{\overline{\Lambda }}_c^{-}{K}^{-})=(1.14\pm 0.15\pm 0.17\pm 0.60)\times {10}^{-3}$ and $\mathcal{B}(B^{-}\to {\Xi }_c^0{\overline{\Lambda }}_c^{-})\times \mathcal{B}({\Xi }_c^0\to {\Xi }^{-}{\pi }^{+})=(2.08\pm 0.65\pm 0.29\pm 0.54)\times {10}^{-5}$, where the uncertainties are statistical, systematic, and from the branching fraction $\mathcal{B}({\Lambda }_c^{+}\to p{K}^{-}{\pi }^{+})$, respectively. We also set upper limits at the 90% confidence level on two other modes: $\mathcal{B}({\overline{B}}^0\to {\Xi }_c^{+}{\overline{\Lambda }}_c^{-})\times \mathcal{B}({\Xi }_c^{+}\to {\Xi }^{-}{\pi }^{+}{\pi }^{+})<5.6\times {10}^{-5}$ and $\mathcal{B}({\overline{B}}^0\to {\Lambda }_c^{+}{\overline{\Lambda }}_c^{-}{\overline{K}}^0)<1.5\times {10}^{-3}$. We observe structure centered at an invariant mass of $2.93\mathrm{GeV}/c^2$ in the ${\Lambda }_c^{+}{K}^{-}$ mass distribution of the decay $B^{-}\to {\Lambda }_c^{+}{\overline{\Lambda }}_c^{-}{K}^{-}$.

We present explicit solutions of the signum-Gordon scalar field equation which have finite energy and are periodic in time. Such oscillons have strictly finite size. They do not emit radiation.

A general approach to viable modified $f(R)$ gravity is developed in both the Jordan and the Einstein frames. A class of exponential, realistic modified gravities is introduced and investigated with care. Special focus is made on step-class models, most promising from the phenomenological viewpoint and which provide a natural way to classify all viable modified gravities. One- and two-step models are explicitly considered, but the analysis is extensible to $N$-step models. Both inflation in the early universe and the onset of recent accelerated expansion arise in these models in a natural, unified way. Moreover, it is demonstrated that models in this category easily pass all local tests, including stability of spherical body solution, nonviolation of Newton’s law, and generation of a very heavy positive mass for the additional scalar degree of freedom.

Domain wall solitons are the simplest topological objects in field theories. The conventional translational symmetry in a field theory is the generator of a one-parameter family of domain wall solutions, and induces a massless moduli field which propagates along a domain wall. We study similar issues in braided noncommutative field theories possessing Hopf algebraic translational symmetries. As a concrete example, we discuss a domain wall soliton in the scalar ${\varphi }^4$ braided noncommutative field theory in Lie-algebraic noncommutative space-time, $[x^i,x^j]=2i\kappa {ϵ}^{ijk}{x}_k$ $(i,j,k=1,2,3)$, which has a Hopf algebraic translational symmetry. We first discuss the existence of a domain wall soliton in view of Derrick’s theorem, and construct explicitly a one-parameter family of solutions in perturbation of the noncommutativity parameter $\kappa$. We then find the massless moduli field which propagates on the domain wall soliton. We further extend our analysis to the general Hopf algebraic translational symmetry.

We investigate the chiral odd generalized parton distributions (GPDs) for the quantum fluctuations of an electron in QED. This provides a field theory inspired model of a relativistic spin-$\frac{1}{2}$ composite state with the correct correlation between the different light-front wave functions (LFWFs) in Fock space. We express the GPDs in terms of overlaps of LFWFs and obtain their representation in impact parameter space when the momentum transfer is purely transverse. We show the spin-orbit correlation effect of the two-particle LFWF as well as the correlation between the constituent spin and the transverse spin of the target.