Current observational bounds on dark energy depend on our assumptions about the curvature of the universe. We present a simple and efficient method for incorporating constraints from cosmic microwave background (CMB) anisotropy data and use it to derive constraints on cosmic curvature and dark energy density as a free function of cosmic time using current CMB, Type Ia supernova (SN Ia), and baryon acoustic oscillation data. We show that there are two CMB shift parameters, $R\equiv \sqrt{{\Omega }_m{H}_0^2}r(z_{\mathrm{CMB}})$ (the scaled distance to recombination) and $l_a\equiv \pi r(z_{\mathrm{CMB}})/r_s(z_{\mathrm{CMB}})$ (the angular scale of the sound horizon at recombination), with measured values that are nearly uncorrelated with each other. Allowing nonzero cosmic curvature, the three-year WMAP (Wilkinson Microwave Anisotropy Probe) data give $R=1.71\pm 0.03$, $l_a=302.5\pm 1.2$, and ${\Omega }_b{h}^2=0.02173\pm 0.00082$, independent of the dark energy model. The corresponding bounds for a flat universe are $R=1.70\pm 0.03$, $l_a=302.2\pm 1.2$, and ${\Omega }_b{h}^2=0.022\pm 0.00082$. We give the covariance matrix of $(R,l_a,{\Omega }_b{h}^2)$ from the three-year WMAP data. We find that $(R,l_a,{\Omega }_b{h}^2)$ provide an efficient and intuitive summary of CMB data as far as dark energy constraints are concerned. Assuming the Hubble Space Telescope (HST) prior of $H_0=72\pm 8(\mathrm{km}/\mathrm{s}){\mathrm{Mpc}}^{-1}$, using 182 SNe Ia (from the HST/GOODS program, the first year Supernova Legacy Survey, and nearby SN Ia surveys), $(R,l_a,{\Omega }_b{h}^2)$ from WMAP three-year data, and SDSS (Sloan Digital Sky Survey) measurement of the baryon acoustic oscillation scale, we find that dark energy density is consistent with a constant in cosmic time, with marginal deviations from a cosmological constant that may reflect current systematic uncertainties or true evolution in dark energy. A flat universe is allowed by current data: ${\Omega }_k=-{0.006}_{-0.012-0.025}^{+0.013+0.025}$ for assuming that the dark energy equation of state $w_X(z)$ is constant, and ${\Omega }_k=-{0.002}_{-0.018-0.032}^{+0.018+0.041}$ for $w_X(z)=w_0+w_a(1-a)$ (68% and 95% confidence levels). The bounds on cosmic curvature are less stringent if dark energy density is allowed to be a free function of cosmic time, and are also dependent on the assumption about the early time property of dark energy. We demonstrate this by studying two examples. Significant improvement in dark energy and cosmic curvature constraints is expected as a result of future dark energy and CMB experiments.

In this paper we compute electroweak contributions to the production of squark pairs at hadron colliders. These include the exchange of electroweak gauge bosons in the $s$-channel as well as electroweak gaugino exchange in the $t$- and/or $u$-channel. In many cases these can interfere with the dominant QCD contributions. As a result, we find sizable contributions to the production of two $SU(2)$ doublet squarks. At the LHC, they amount to 10% to 20% for typical mSUGRA (or CMSSM) scenarios, but in more general scenarios they can vary between $-40\%$ and $+55\%$, depending on size and sign of the $SU(2)$ gaugino mass. The electroweak contribution to the total squark pair production rate at the LHC is about 3.5 times smaller.

We carry out a detailed analysis of the scalar sector of the nonminimal supersymmetric standard model with lepton number violation, and study the constraints imposed on it by the stability of the electroweak symmetry breaking vacuum. The model contains a trilinear lepton number violating term in the superpotential together with the associated supersymmetry breaking interactions which can give rise to neutrino masses. We evaluate the mass matrices for the various boson and fermion modes and then discuss the effect that the lepton number violating interactions have on the mass spectra using a phenomenological prescription to implement the experimental constraints on the light neutrinos mass matrix. We also discuss qualitatively the conditions on the lepton number violating parameters set by the unbounded from below directions, and from the absence of the charge and color breaking minima in this model.

The possibility of a strongly first-order electroweak phase transition is established in the minimal supersymmetric standard model with an extra $U(1{)}^{\prime }$, where a nontrivial $CP$ violating phase is introduced in its Higgs sector. We find that there is some region in the parameter space of the model that allows the strongly first-order electroweak phase transition. The mass of the stop quark need not be smaller than the top quark mass to ensure the first-order electroweak phase transition be strong. The effect of the $CP$ violating phase upon the strength of the phase transition is discovered. The strength of the phase transition is reduced when the size of the $CP$ violation is increased. For a given $CP$ violating phase, we find that the model has a larger mass for the lightest Higgs boson when it has a stronger phase transition.

We compute the two-loop renormalization functions, in the $R{I}^{\prime }$ scheme, of local bilinear quark operators $\overline{\psi }\Gamma \psi$, where $\Gamma$ denotes the scalar and pseudoscalar Dirac matrices, in the lattice formulation of QCD. We consider both the flavor nonsinglet and singlet operators; the latter, in the scalar case, leads directly to the two-loop fermion mass renormalization, $Z_m$. As a prerequisite for the above, we also compute the quark field renormalization, $Z_{\psi }$, up to two loops. We use the clover action for fermions and the Wilson action for gluons. Our results are given as a polynomial in $c_{\mathrm{SW}}$, in terms of both the renormalized and bare coupling constants, in the renormalized Feynman gauge. We also confirm the one-loop renormalization functions, for generic gauge. Finally, we present our results in the $\overline{MS}$ scheme, for easier comparison with calculations in the continuum. The corresponding results, for fermions in an arbitrary representation, are included in the Appendix.

Using soft-collinear effective theory we describe at leading order in $1/m_b$ all the semi-inclusive hadronic $B\to XM$ decays near the endpoint, where an energetic light meson $M$ recoils against an inclusive jet $X$. Here we extend to the decays in which spectator quarks go into the jet $X$, and also include the decays involving $\eta$, ${\eta }^{\prime }$ mesons that receive additional contributions from gluonic operators. The predicted branching ratios and $CP$ asymmetries depend on fewer hadronic parameters than the corresponding two-body $B$ decays. This makes semi-inclusive hadronic $B\to XM$ decays a powerful probe of the potential nonperturbative nature of charming penguins as well as a useful probe of new physics effects in electroweak flavor changing transitions. A comparison with $B\to KX$ data from BABAR points to an enhanced charming penguin, albeit with large experimental errors.

We compute numerically the absorption cross section of a canonical acoustic hole for sound waves with arbitrary frequencies. Our outputs are in full agreement with the expected low- and high-frequency limits.

Turning on a Neveu-Schwarz–Neveu-Schwarz (NS-NS) three-form flux in a compact space drives some D-branes to be either Freed-Witten anomalous or unstable to decay into fluxes by the appearance of instantonic branes. By applying $T$-duality on a toroidal compactification, the NS flux is transformed into metric fluxes. We propose a $T$-dual version of the Atiyah-Hirzebruch Spectral Sequence upon which we describe the Freed-Witten anomaly and the brane-flux transition driven by NS and metric fluxes in a twisted torus. The required conditions to cancel the anomaly and the appearance of new instantonic branes are also described. In addition, we give an example in which all D6-branes wrapping Freed-Witten anomaly-free three-cycles in ${\tilde{T}}^6/{\mathbb{Z}}_2\times {\mathbb{Z}}_2$ are nevertheless unstable to decay into fluxes. Even more we find a topological transformation between Ramond-Ramond, NS-NS, and metric fluxes driven by a chain of instantonic branes.

The influence of Lorentz- and $CPT$-violating terms of the extended standard model on a semiclassical two-level system is analyzed. It is shown that the Lorentz-violating background (when coupled with the fermion sector in a vector way) is able to induce modifications on the Rabi oscillation pattern, promoting sensitive modulations on the usual oscillations. As for the term involving the coefficient coupled in an axial vector way, it brings about oscillations both on energy states and on the spin states (implied by the background). It is also seen that such backgrounds are able to yield state oscillations even in the absence of the electromagnetic field. The foreseen effects are used to establish upper bounds on the Lorentz-violating coefficients.

In a remarkable numerical analysis of the spectrum of states for a spherically symmetric black hole in loop quantum gravity, Corichi, Diaz-Polo and Fernandez-Borja found that the entropy of the black hole horizon increases in what resembles discrete steps as a function of area. In the present article we reformulate the combinatorial problem of counting horizon states in terms of paths through a certain space. This formulation sheds some light on the origins of this steplike behavior of the entropy. In particular, using a few extra assumptions we arrive at a formula that reproduces the observed step length to a few tenths of a percent accuracy. However, in our reformulation the periodicity ultimately arises as a property of some complicated process, the properties of which, in turn, depend on the properties of the area spectrum in loop quantum gravity in a rather opaque way. Thus, in some sense, a deep explanation of the observed periodicity is still lacking.

We present an accurate approximation of the full gravitational radiation waveforms generated in the merger of noneccentric systems of two nonspinning black holes. Utilizing information from recent numerical relativity simulations and the natural flexibility of the effective-one-body (EOB) model, we extend the latter so that it can successfully match the numerical relativity waveforms during the last stages of inspiral, merger, and ringdown. By “successfully” here, we mean with phase differences $\lesssim 8\%$ of a gravitational-wave cycle accumulated by the end of the ringdown phase, maximizing only over time of arrival and initial phase. We obtain this result by simply adding a 4-post-Newtonian order correction in the EOB radial potential and determining the (constant) coefficient by imposing high-matching performances with numerical waveforms of mass ratios $m_1/m_2=1$, $3/2$, 2 and 4, $m_1$ and $m_2$ being the individual black-hole masses. The final black-hole mass and spin predicted by the numerical simulations are used to determine the ringdown frequency and decay time of three quasinormal-mode damped sinusoids that are attached to the EOB inspiral-(plunge) waveform at the EOB light ring. The EOB waveforms might be tested and further improved in the future by comparison with extremely long and accurate inspiral numerical relativity waveforms. They may be already employed for coherent searches and parameter estimation of gravitational waves emitted by nonspinning coalescing binary black holes with ground-based laser-interferometer detectors.

We consider real and complex scalar fields nonminimally coupled to gravity in the bulk spacetime and study their impact on the brane upon acquiring a nonvanishing vacuum expectation value. When examining the case of the complex scalar field, a minimally coupled $U(1)$ gauge field is also considered so that spontaneous symmetry breaking can take place. Particular attention is paid to the terms arising from the junction conditions, which act towards reinforcing the mechanism of spontaneous symmetry breaking. We find that the embedding of a braneworld universe in a bulk spacetime endowed with matter fields can induce this mechanism at very high energies and that matter localized on the brane will only interact with bulk matter fields through gravity when a nonminimal coupling exists.

We consider the cosmology of the Ricci-tensor-squared gravity in the Palatini variational approach. The gravitational action of standard general relativity is modified by adding a function $f(R^{ab}{R}_{ab})$ to the Einstein-Hilbert action, and the Palatini variation is used to derive the field equations. A general method of obtaining the background and first-order covariant and gauge-invariant perturbation equations is outlined. As an example, we consider the cosmological constraints on such theories arising from the supernova type Ia and cosmic microwave background observations. We find that the best fit to the data is a non-null leading-order correction to Einstein gravity, but the current data exhibit no significant preference over the concordance model. The growth of nonrelativistic matter density perturbations at late times is also analyzed, and we find that a scale-dependent (positive or negative) sound-speed-squared term generally appears in the growth equation for small-scale density perturbations. We also estimate the observational bound imposed by the matter power spectrum for the model with $f({\mathbf{R}}^{ab}{\mathbf{R}}_{ab})=\alpha ({\mathbf{R}}^{ab}{\mathbf{R}}_{ab}{)}^{\beta }$ to be roughly $|\beta |\lesssim \mathcal{O}({10}^{-5})$ so long as the dark matter does not possess compensating anisotropic stresses.

The visibility of the shell-focusing singularity in Szekeres space-time—which represents quasispherical dust collapse—has been studied on numerous occasions in the context of the cosmic censorship conjecture. The various results derived have assumed that there exist radial null geodesics in the space-time. We show that such geodesics do not exist in general, and so previous results on the visibility of the singularity are not generally valid. More precisely, we show that the existence of a radial geodesic in Szekeres space-time implies that the space-time is axially symmetric, with the geodesic along the polar direction (i.e. along the axis of symmetry). If there is a second nonparallel radial geodesic, then the space-time is spherically symmetric, and so is a Lemaître-Tolman-Bondi space-time. For the case of the polar geodesic in an axially symmetric Szekeres space-time, we give conditions on the free functions (i.e. initial data) of the space-time which lead to visibility of the singularity along this direction. Likewise, we give a sufficient condition for censorship of the singularity. We point out the complications involved in addressing the question of visibility of the singularity both for nonradial null geodesics in the axially symmetric case and in the general (nonaxially symmetric) case, and suggest a possible approach.

Dark matter annihilation in so-called spikes near black holes is believed to be an important method of indirect dark matter detection. In the case of circular particle orbits, the density profile of dark matter has a plateau at small radii, the maximal density being limited by the annihilation cross section. However, in the general case of arbitrary velocity anisotropy the situation is different. Particularly, for isotropic velocity distribution the density profile cannot be shallower than $r^{-1/2}$ in the very center. Indeed, a detailed study reveals that in many cases the term “annihilation plateau” is misleading, as the density actually continues to rise towards small radii and forms a weak cusp, $\rho \propto r^{-(\beta +1/2)}$, where $\beta$ is the anisotropy coefficient. The annihilation flux, however, does not change much in the latter case, if averaged over an area larger than the annihilation radius.

We consider a phenomenological modification of the pre-big-bang scenario using ideas from the resolution of curvature singularities in loop quantum cosmology. We show that nonperturbative loop modifications to the dynamics, arising from the underlying polymer representation, can resolve the graceful exit problem. The curvature and the dilaton energy stay finite at all times, in both the string and Einstein frames. In the string frame, the dilaton tends to a constant value at late times after the bounce.

We compute the difference in decay widths between charged and neutral $\rho (770)$ vector mesons. The isospin breaking arising from mass differences of neutral and charged $\pi$ and $\rho$ mesons, radiative corrections to $\rho \to \pi \pi$, and the $\rho \to \pi \pi \gamma$ decays are taken into account. It is found that the width difference $\Delta {\Gamma }_{\rho }$ is very sensitive to the isospin breaking in the $\rho$ meson mass, $\Delta m_{\rho }$. This result can be useful to test the correlations observed between the values of these parameters extracted from experimental data.

We study the temperature dependence of the pseudoscalar meson properties in a relativistic bound-state approach exhibiting the chiral behavior mandated by QCD. Concretely, we adopt the Dyson-Schwinger approach with a rank-2 separable model interaction. After extending the model to the strange sector and fixing its parameters at zero temperature, $T=0$, we study the $T$ dependence of the masses and decay constants of all ground-state mesons in the pseudoscalar nonet. Of chief interest are $\eta$ and ${\eta }^{\prime }$. The influence of the QCD axial anomaly on them is successfully obtained through the Witten-Veneziano relation at $T=0$. The same approach is then extended to $T>0$, using lattice QCD results for the topological susceptibility. The most conspicuous finding is an increase of the ${\eta }^{\prime }$ mass around the chiral restoration temperature $T_{\mathrm{Ch}}$, which would suggest a suppression of ${\eta }^{\prime }$ production in relativistic heavy-ion collisions. The increase of the ${\eta }^{\prime }$ mass may also indicate that the extension of the Witten-Veneziano relation to finite temperatures becomes unreliable around and above $T_{\mathrm{Ch}}$. Possibilities of an improved treatment are discussed.

We compute supersymmetric contributions to pion leptonic (${\pi }_{l2}$) decays in the minimal supersymmetric standard model (MSSM). When R-parity is conserved, the largest contributions to the ratio $R_{e/\mu }\equiv \Gamma [{\pi }^{+}\to e^{+}{\nu }_e(\gamma )]/\Gamma [{\pi }^{+}\to {\mu }^{+}{\nu }_{\mu }(\gamma )]$ arise from one-loop $(V-A)\otimes (V-A)$ corrections. These contributions can be potentially as large as the sensitivities of upcoming experiments; if measured, they would imply significant bounds on the chargino and slepton sectors complementary to current collider limits. We also analyze R-parity-violating interactions, which may produce a detectable deviation in $R_{e/\mu }$ while remaining consistent with all other precision observables.

We explore constraints on the charged Higgs sector in the left-right symmetric model from the present experimental data. Because of the different Yukawa structure, the allowed parameter space of the charged Higgs boson in the LR model is different from that of the two Higgs doublet model. We find that the constraint from $t\to b{H}^{\pm }$ decay at Tevatron is most significant, while $B\to \tau \nu$ decay could provide no constraint on the LR model. Bounds from $e^{-}{e}^{+}\to H^{-}{H}^{+}$ process at LEP are similar to those in the two Higgs doublet model.