The string effective action at tree level contains, in its bosonic sector, the Einstein-Hilbert term, the dilaton, and the axion, besides scalar and gauge fields coming from the Ramond-Ramond sector. The reduction to four dimensions brings to scene moduli fields. We generalize this effective action by introducing two arbitrary parameters, $\omega$ and $m$, connected with the dilaton and axion couplings. In this way, more general frameworks can be analyzed. Regular solutions with a bounce can be obtained for a range of (negative) values of the parameter $\omega$ which, however, exclude the pure string configuration ($\omega =-1$). We study the evolution of scalar perturbations in such cosmological scenarios. The predicted primordial power spectrum decreases with the wave number with spectral index $n_s=-2$, in contradiction with the results of the Wilkinson microwave anisotropy probe (WMAP). Hence, all such effective string motivated cosmological bouncing models seem to be ruled out, at least at the tree level approximation.

A cosmological theory that predicts a late-time accelerated attractor with a constant dark matter to dark energy ratio can be said to solve the coincidence problem. Such cosmologies are naturally generated in the context of nonstandard gravity theories under conformal transformation because of the resulting couplings between scalar fields and matter. The present work examines four classes of these transformed theories and finds that only a small subset-those with a single scalar field-are capable of solving the coincidence problem.

Though the predictions of the standard model (SM) are in excellent agreement with experiments there are still several theoretical problems, such as fine-tuning and the hierarchy problem. These problems are associated with the Higgs sector of the SM, where it is widely believed that some “new physics” will take over at the TeV scale. One beyond the SM theory which resolves these problems is the little Higgs model. In this work we shall investigate the effects of the little Higgs model on $\gamma \gamma \to \gamma \gamma$ scattering, where the process $\gamma \gamma \to \gamma \gamma$ at high energies occurs in the SM through diagrams involving $W$, charged quark, and lepton loops (and is, therefore, particularly sensitive to any new physics).

Staggered chiral perturbation theory ($\mathrm{S}\chi \mathrm{PT}$) takes into account the “fourth-root trick” for reducing unwanted (taste) degrees of freedom with staggered quarks by multiplying the contribution of each sea quark loop by a factor of $1/4$. In the special case of four staggered fields (four flavors, $n_F=4$), I show here that certain assumptions about analyticity and phase structure imply the validity of this procedure for representing the rooting trick in the chiral sector. I start from the observation that, when the four flavors are degenerate, the fourth root simply reduces $n_F=4$ to $n_F=1$. One can then treat nondegenerate quark masses by expanding around the degenerate limit. With additional assumptions on decoupling, the result can be extended to the more interesting cases of $n_F=3$, 2, or 1. An apparent paradox associated with the one-flavor case is resolved. Coupled with some expected features of unrooted staggered quarks in the continuum limit, in particular, the restoration of taste symmetry, $\mathrm{S}\chi \mathrm{PT}$ then implies that the fourth-root trick induces no problems (for example, a violation of unitarity that persists in the continuum limit) in the lowest energy sector of staggered lattice QCD. It also says that the theory with staggered valence quarks and rooted staggered sea quarks behaves like a simple, partially-quenched theory, not like a mixed theory in which sea and valence quarks have different lattice actions. In most cases, the assumptions made in this paper are not only sufficient but also necessary for the validity of $\mathrm{S}\chi \mathrm{PT}$, so that a variety of possible new routes for testing this validity are opened.

The use of improved staggered actions (HYP, Asqtad) has been proved to reduce the scaling corrections that affected previous calculations of $B_K$ with unimproved (standard) staggered fermions in the quenched approximation. This improved behavior allows us to perform a reliable calculation of $B_K$ including quark vacuum polarization effects, using the MILC configurations with $n_f=2+1$ flavors of sea fermions. We perform such a calculation for a single lattice spacing, $a=0.125\mathrm{fm}$, and with kaons made up of degenerate quarks with $m_s/2$. The valence strange quark mass $m_s$ is fixed to its physical value and we use two different values of the light sea quark masses. After a chiral extrapolation of the results to the physical value of the sea quark masses, we find ${\widehat{B}}_K=0.83\pm 0.18$, where the error is dominated by the uncertainty in the lattice to continuum matching at $\mathcal{O}({\alpha }_s^2)$. The matching will need to be improved to get the precision needed to make full use of the experimental data on ${\epsilon }_K$ to constrain the unitarity triangle.

It is an open challenge to analyze the crystalline color superconducting phases that may arise in cold dense, but not asymptotically dense, three-flavor quark matter. At present the only approximation within which it seems possible to compare the free energies of the myriad possible crystal structures is the Ginzburg-Landau approximation. Here, we test this approximation on a particularly simple “crystal” structure in which there are only two condensates $⟨us⟩\sim \Delta \exp (i{\mathbf{q}}_{\mathbf{2}}·\mathbf{r})$ and $⟨ud⟩\sim \Delta \exp (i{\mathbf{q}}_{\mathbf{3}}·\mathbf{r})$ whose position-space dependence is that of two plane waves with wave vectors ${\mathbf{q}}_{\mathbf{2}}$ and ${\mathbf{q}}_{\mathbf{3}}$ at arbitrary angles. For this case, we are able to solve the mean-field gap equation without making a Ginzburg-Landau approximation. We find that the Ginzburg-Landau approximation works in the $\Delta \to 0$ limit as expected, find that it correctly predicts that $\Delta$ decreases with increasing angle between ${\mathbf{q}}_{\mathbf{2}}$ and ${\mathbf{q}}_{\mathbf{3}}$ meaning that the phase with ${\mathbf{q}}_{\mathbf{2}}\parallel {\mathbf{q}}_{\mathbf{3}}$ has the lowest free energy, and find that the Ginzburg-Landau approximation is conservative in the sense that it underestimates $\Delta$ at all values of the angle between ${\mathbf{q}}_{\mathbf{2}}$ and ${\mathbf{q}}_{\mathbf{3}}$.

An analytic resolution of the covariant oscillator quark model for a three-body system is presented. Our harmonic potential is a general quadratic potential which can simulate both a $\Delta$-shape configuration or a simplified Y-configuration where the junction is located at the center of mass. The mass formulas obtained are used to compute glueball and baryon spectra. We show that the agreement with lattice and experimental data is correct if the Casimir scaling hypothesis is assumed. It is also argued that our model is compatible with pomeron and odderon approaches.

The transition form factors of the semileptonic decay $B_s$ into scalar $D_{s_0}(2317)$ meson is calculated in the framework of 3-point QCD sum rule. The branching ratio is found to be $\sim {10}^{-3}$ for the $B_s\to D_{s_0}(2317)\ell {\overline{\nu }}_{\ell }(\ell =e,\mu )$ decay, and $\sim {10}^{-4}$ for the $B_s\to D_{s_0}(2317)\tau {\overline{\nu }}_{\tau }$ decay, respectively.

We test whether or not the $\tau$ lepton manifests the same couplings as the $\mu$ lepton by investigating the relative decay rates in purely leptonic $D^{+}$ meson decays. We use $281{\mathrm{pb}}^{-1}$ of data accumulated at the $\psi (3770)$ resonance with the CLEO-c detector, to limit $\mathcal{B}(D^{+}\to {\tau }^{+}\nu )<2.1\times {10}^{-3}$ at 90% confidence level (C.L.), thus allowing us to place the first upper limit on the ratio $R=\Gamma (D^{+}\to {\tau }^{+}\nu )/\Gamma (D^{+}\to {\mu }^{+}\nu )$. The ratio of $R$ to the standard model expectation of 2.65 then is $<1.8$ at 90% C.L., consistent with the prediction of lepton universality.

We present measurements of the branching fractions and charge asymmetries of $B$ decays to all $D^{(*)}{\overline{D}}^{(*)}$ modes. Using $232\times {10}^6$ $B\overline{B}$ pairs recorded on the $\mathit{{\rm Y}}(4S)$ resonance by the BABAR detector at the $e^{+}{e}^{-}$ asymmetric $B$ factory PEP-II at the Stanford Linear Accelerator Center, we measure the branching fractions $\mathcal{B}(B^0\to D^{*+}{D}^{*-})=(8.1\pm 0.6\pm 1.0)\times {10}^{-4}$, $\mathcal{B}(B^0\to D^{*\pm }{D}^{\mp })=(5.7\pm 0.7\pm 0.7)\times {10}^{-4}$, $\mathcal{B}(B^0\to D^{+}{D}^{-})=(2.8\pm 0.4\pm 0.5)\times {10}^{-4}$, $\mathcal{B}(B^{+}\to D^{*+}{\overline{D}}^{*0})=(8.1\pm 1.2\pm 1.2)\times {10}^{-4}$, $\mathcal{B}(B^{+}\to D^{*+}{\overline{D}}^0)=(3.6\pm 0.5\pm 0.4)\times {10}^{-4}$, $\mathcal{B}(B^{+}\to D^{+}{\overline{D}}^{*0})=(6.3\pm 1.4\pm 1.0)\times {10}^{-4}$, and $\mathcal{B}(B^{+}\to D^{+}{\overline{D}}^0)=(3.8\pm 0.6\pm 0.5)\times {10}^{-4}$, where in each case the first uncertainty is statistical and the second systematic. We also determine the limits $\mathcal{B}(B^0\to D^{*0}{\overline{D}}^{*0})<0.9\times {10}^{-4}$, $\mathcal{B}(B^0\to D^{*0}{\overline{D}}^0)<2.9\times {10}^{-4}$, and $\mathcal{B}(B^0\to D^0{\overline{D}}^0)<0.6\times {10}^{-4}$, each at 90% confidence level. All decays above denote either member of a charge-conjugate pair. We also determine the $CP$-violating charge asymmetries $\mathcal{A}(B^0\to D^{*\pm }{D}^{\mp })=0.03\pm 0.10\pm 0.02$, $\mathcal{A}(B^{+}\to D^{*+}{\overline{D}}^{*0})=-0.15\pm 0.11\pm 0.02$, $\mathcal{A}(B^{+}\to D^{*+}{\overline{D}}^0)=-0.06\pm 0.13\pm 0.02$, $\mathcal{A}(B^{+}\to D^{+}{\overline{D}}^{*0})=0.13\pm 0.18\pm 0.04$, and $\mathcal{A}(B^{+}\to D^{+}{\overline{D}}^0)=-0.13\pm 0.14\pm 0.02$. Additionally, when we combine these results with information from time-dependent $CP$ asymmetries in $B^0\to D^{(*)+}{D}^{(*)-}$ decays and world-averaged branching fractions of $B$ decays to $D_s^{(*)}{\overline{D}}^{(*)}$ modes, we find the Cabibbo-Kobayashi-Maskawa phase $\gamma$ is favored to lie in the range (0.07–2.77) radians (with a $+0$ or $+\pi$ radians ambiguity) at 68% confidence level.

A search for the decay of the $\tau$ lepton to five charged and two neutral pions is performed using data collected by the BABAR detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider. The analysis uses $232{\mathrm{fb}}^{-1}$ of data at center-of-mass energies on or near the ${\rm Y}(4S)$ resonance. We observe 10 events with an expected background of ${6.5}_{-1.4}^{+2.0}$ events. In the absence of a signal, we set the limit on the branching ratio $\mathcal{B}({\tau }^{-}\to 3{\pi }^{-}2{\pi }^{+}2{\pi }^0{\nu }_{\tau })<3.4\times {10}^{-6}$ at the 90% confidence level. This is a significant improvement over the previously established limit. In addition, we search for the decay mode ${\tau }^{-}\to 2\omega {\pi }^{-}{\nu }_{\tau }$. We observe 1 event with an expected background of $0.4\genfrac{}{}{0ex}{}{+1.0}{-0.4}$ events and calculate the upper limit $\mathcal{B}({\tau }^{-}\to 2\omega {\pi }^{-}{\nu }_{\tau })<5.4\times {10}^{-7}$ at the 90% confidence level. This is the first upper limit for this mode.

We report a measurement of the charge asymmetry for same-sign dileptons in $B^0-{\overline{B}}^0$ mixing, $A_{\mathrm{sl}}$. The data were collected with the Belle detector at KEKB. Using a data sample of $78{\mathrm{fb}}^{-1}$ recorded at the ${\rm Y}(4S)$ resonance and $9{\mathrm{fb}}^{-1}$ recorded at an energy 60 MeV below the resonance, we measure $A_{\mathrm{sl}}=(-1.1\pm 7.9(\mathrm{\text{stat}})\pm 8.5(\mathrm{\text{sys}}))\times {10}^{-3}$.

We investigate the mass spectrum of $1^{+}$ exotic mesons with quark content $(\mathbf{c}\mathbf{s}\overline{\mathbf{c}}\overline{\mathbf{q}})/(\mathbf{c}\mathbf{q}\overline{\mathbf{c}}\overline{\mathbf{s}})$, using molecular and diquark-antidiquark operators, in quenched lattice QCD with exact chiral symmetry. For the molecular operator $\{(\overline{\mathbf{q}}{\gamma }_i\mathbf{c})(\overline{\mathbf{c}}{\gamma }_5\mathbf{s})-(\overline{\mathbf{c}}{\gamma }_i\mathbf{s})(\overline{\mathbf{q}}{\gamma }_5\mathbf{c})\}$ and the diquark-antidiquark operator $\{[{\mathbf{q}}^{T}C{\gamma }_i\mathbf{c}][\overline{\mathbf{s}}C{\gamma }_5{\overline{\mathbf{c}}}^T]-[{\mathbf{q}}^{T}C{\gamma }_5\mathbf{c}][\overline{\mathbf{s}}C{\gamma }_i^T{\overline{\mathbf{c}}}^T]\}$, both detect a $1^{+}$ resonance with mass around $4010\pm 50\mathrm{MeV}$ in the limit $m_q\to m_{u,d}$.

The dynamics of warped/flux compactifications is studied, including warping effects, providing a firmer footing for investigation of the “landscape.” We present a general formula for the four-dimensional potential of warped compactifications in terms of ten-dimensional quantities. This allows a systematic investigation of moduli-fixing effects and potentials for mobile branes. We provide a necessary criterion, “slope dominance,” for evading “no-go” results for de Sitter vacua. We outline the ten-dimensional derivation of the nonperturbative effects that should accomplish this in examples of Kachru, Kallosh, Linde and Trivedi and outline a systematic discussion of their corrections. We show that potentials for mobile branes receive generic contributions inhibiting slow-roll inflation. We give a linearized analysis of general scalar perturbations of warped IIB compactifications, revealing new features for both time-independent and dependent moduli, and new aspects of the kinetic part of the four-dimensional effective action. The universal Kahler modulus is found not to be a simple scaling of the internal metric, and a prescription is given for defining holomorphic Kahler moduli, including warping effects. In the presence of mobile branes, this prescription elucidates couplings between bulk and brane fields. Our results are thus relevant to investigations of the existence of de Sitter vacua in string theory, and of their phenomenology, cosmology, and statistics.

We study a $d=2+1$ dimensional Chern-Simons gauge theory coupled to a Higgs scalar and an axion field, finding the form of the potential that allows the existence of self-dual equations and the corresponding Bogomolny bound for the energy of static configurations. We show that the same conditions allow for the $N=2$ supersymmetric extension of the model, reobtaining the BPS equations from the supersymmetry requirement. Explicit electrically charged vortexlike solutions to these equations are presented.

Coset methods are used to construct the action describing the dynamics associated with the spontaneous breaking of the local supersymmetries. The resulting action is an invariant form of the Einstein-Hilbert action, which in addition to the gravitational vierbein, also includes a massive gravitino field. Invariant interactions with matter and gauge fields are also constructed. The effective Lagrangian describing processes involving the emission or absorption of a single light gravitino is analyzed.

We obtain an efficient description for the dynamics of nonspinning compact binaries moving in inspiralling eccentric orbits to implement the phasing of gravitational waves from such binaries at the 3.5 post-Newtonian (PN) order. Our computation heavily depends on the phasing formalism, presented in [T. Damour, A. Gopakumar, and B. R. Iyer, Phys. Rev. D 70, 064028 (2004)], and the 3PN accurate generalized quasi-Keplerian parametric solution to the conservative dynamics of nonspinning compact binaries moving in eccentric orbits, available in [R.-M. Memmesheimer, A. Gopakumar, and G. Schäfer, Phys. Rev. D 70, 104011 (2004)]. The gravitational-wave (GW) polarizations $h_{+}$ and $h_{\times }$ with 3.5PN accurate phasing should be useful for the earth-based GW interferometers, current and advanced, if they plan to search for gravitational waves from inspiralling eccentric binaries. Our results will be required to do astrophysics with the proposed space-based GW interferometers like LISA, BBO, and DECIGO.

We study the effects of unstable gravitino on big-bang nucleosynthesis. If the gravitino mass is smaller than $\sim 10\mathrm{TeV}$, primordial gravitinos produced after inflation are likely to decay after big-bang nucleosynthesis starts, and light-element abundances may be significantly affected by hadro and photodissociation processes as well as by $p\leftrightarrow n$ conversion process. We calculate the light-element abundances and derive upper bounds on the reheating temperature after inflation. In our analysis, we calculate decay parameters of the gravitino (i.e. lifetime and branching ratios) in detail. In addition, we perform a systematic study of the hadron spectrum produced by the gravitino decay, taking account of all the hadrons produced by the decay products of the gravitino (including the daughter superparticles). We discuss model dependence of the upper bound on the reheating temperature.

The interacting and holographic dark energy models involve two important quantities. One is the characteristic size of the holographic bound and the other is the coupling term of the interaction between dark energy and dark matter. Rather than fixing either of them, we present a detailed study of theoretical relationships among these quantities and cosmological parameters as well as observational constraints in a general formalism. In particular, we argue that the ratio of dark matter to dark energy density depends on the choice of these two quantities, thus providing a mechanism to change the evolution history of the ratio from that in standard cosmology such that the coincidence problem may be solved. We investigate this problem in detail and construct explicit models to demonstrate that it may be alleviated provided that the interacting term and the characteristic size of holographic bound are appropriately specified. Furthermore, these models are well fitted with the current observation at least in the low redshift region.

Using the effective Lagrangian method, we analyze the electroweak corrections to the anomalous dipole moments of leptons from some special two-loop topological diagrams which are composed of neutralino-slepton (chargino-sneutrino) in the minimal supersymmetric extension of the standard model (MSSM). Considering the translational invariance of the inner loop momenta and the electromagnetic gauge invariance, we get all dimension six operators and derive their coefficients. After applying equations of motion to the external leptons, the anomalous dipole moments of leptons are obtained. The numerical results imply that there is a parameter space where the two-loop supersymmetric corrections to the muon anomalous dipole moments may be significant.