We present test results for the smooth lattice method using an Oppenheimer-Snyder spacetime. The results are in excellent agreement with theory and numerical results from other authors.

We consider the asymptotic-safety scenario for quantum gravity which constructs a nonperturbatively renormalizable quantum gravity theory with the help of the functional renormalization group (RG). We verify the existence of a non-Gaussian fixed point and include a running curvature-ghost coupling as a first step towards the flow of the ghost sector of the theory. We find that the scalar curvature-ghost coupling is asymptotically free and RG relevant in the ultraviolet. Most importantly, the property of asymptotic safety discovered so far within the Einstein-Hilbert truncation and beyond remains stable under the inclusion of the ghost flow.

Theories that attempt to explain the observed cosmic acceleration by modifying general relativity all introduce a new scalar degree of freedom that is active on large scales, but is screened on small scales to match experiments. We demonstrate that if such screening occurs via the chameleon mechanism, such as in $f(R)$ theory, it is possible to have order unity violation of the equivalence principle, despite the absence of explicit violation in the microscopic action. Namely, extended objects such as galaxies or constituents thereof do not all fall at the same rate. The chameleon mechanism can screen the scalar charge for large objects but not for small ones (large/small is defined by the depth of the gravitational potential and is controlled by the scalar coupling). This leads to order one fluctuations in the ratio of the inertial mass to gravitational mass. We provide derivations in both Einstein and Jordan frames. In Jordan frame, it is no longer true that all objects move on geodesics; only unscreened ones, such as test particles, do. In contrast, if the scalar screening occurs via strong coupling, such as in the Dvali-Gabadadze-Porrati braneworld model, equivalence principle violation occurs at a much reduced level. We propose several observational tests of the chameleon mechanism: 1. small galaxies should accelerate faster than large galaxies, even in environments where dynamical friction is negligible; 2. voids defined by small galaxies would appear larger compared to standard expectations; 3. stars and diffuse gas in small galaxies should have different velocities, even if they are on the same orbits; 4. lensing and dynamical mass estimates should agree for large galaxies but disagree for small ones. We discuss possible pitfalls in some of these tests. The cleanest is the third one where the mass estimate from HI rotational velocity could exceed that from stars by 30% or more. To avoid blanket screening of all objects, the most promising place to look is in voids.

We consider a gravitational theory of a scalar field $\varphi$ with nonminimal derivative coupling to curvature. The coupling terms have the form ${\kappa }_{1}R{\varphi }_{,\mu }{\varphi }^{,\mu }$ and ${\kappa }_2{R}_{\mu \nu }{\varphi }^{,\mu }{\varphi }^{,\nu }$, where ${\kappa }_1$ and ${\kappa }_2$ are coupling parameters with dimensions of length squared. In general, field equations of the theory contain third derivatives of $g_{\mu \nu }$ and $\varphi$. However, in the case $-2{\kappa }_1={\kappa }_2\equiv \kappa$, the derivative coupling term reads $\kappa G_{\mu \nu }{\varphi }^{,\mu }{\varphi }^{,\nu }$ and the order of corresponding field equations is reduced up to second one. Assuming $-2{\kappa }_1={\kappa }_2$, we study the spatially-flat Friedman-Robertson-Walker model with a scale factor $a(t)$ and find new exact cosmological solutions. It is shown that properties of the model at early stages crucially depend on the sign of $\kappa$. For negative $\kappa$, the model has an initial cosmological singularity, i.e., $a(t)\sim (t-t_i{)}^{2/3}$ in the limit $t\to t_i$; and for positive $\kappa$, the Universe at early stages has the quasi-de Sitter behavior, i.e., $a(t)\sim e^{Ht}$ in the limit $t\to -\infty$, where $H=(3\sqrt{\kappa }{)}^{-1}$. The corresponding scalar field $\varphi$ is exponentially growing at $t\to -\infty$, i.e., $\varphi (t)\sim e^{-t/\sqrt{\kappa }}$. At late stages, the Universe evolution does not depend on $\kappa$ at all; namely, for any $\kappa$ one has $a(t)\sim t^{1/3}$ at $t\to \infty$. Summarizing, we conclude that a cosmological model with nonminimal derivative coupling of the form $\kappa G_{\mu \nu }{\varphi }^{,\mu }{\varphi }^{,\nu }$ is able to explain in a unique manner both a quasi-de Sitter phase and an exit from it without any fine-tuned potential.

It is quite possible that the reheat temperature of the Universe is extremely low close to the scale of big bang nucleosynthesis, i.e. $T_R\sim 1–10\mathrm{MeV}$. At such low reheat temperatures generating matter, antimatter asymmetry and synthesizing dark matter particles are challenging issues which need to be addressed within a framework of beyond the standard model physics. In this paper we point out that a successful cosmology can emerge naturally provided the $R$-parity violating interactions are responsible for the excess in baryons over antibaryons and at the same time they can explain the longevity of dark matter with the right abundance.

We consider a model of the Universe in which the matter content is in the form of discrete islands, rather than a continuous fluid. In the appropriate limits the resulting large-scale dynamics approach those of a Friedmann-Robertson-Walker (FRW) universe. The optical properties of such a space-time, however, do not. This illustrates the fact that the optical and “average” dynamical properties of a relativistic universe are not equivalent, and do not specify each other uniquely. We find the angular diameter distance, luminosity distance, and redshifts that would be measured by observers in these space-times, using both analytic approximations and numerical simulations. While different from their counterparts in FRW, the effects found do not look like promising candidates to explain the observations usually attributed to the existence of dark energy. This incongruity with standard FRW cosmology is not due to the existence of any unexpectedly large structures or voids in the Universe, but only to the fact that the matter content of the Universe is not a continuous fluid.

The properties of matter at ultrahigh densities, low temperatures, and with a significant asymmetry between protons and neutrons can be studied exclusively through astrophysical observations of neutron stars. We show that measurements of the masses and radii of neutron stars can lead to tight constraints on the pressure of matter at three fiducial densities, from 1.85 to 7.4 times the density of nuclear saturation, in a manner that is largely model independent and that captures the key characteristics of the equation of state. We demonstrate that observations with 10% uncertainties of at least three neutron stars can lead to measurements of the pressure at these fiducial densities with an accuracy of 0.11 dex or $\simeq 30\%$. Observations of three neutron stars with 5% uncertainties are sufficient to distinguish at a better than $3\sigma$ confidence level between currently proposed equations of state. In the electromagnetic spectrum, such accurate measurements will become possible for weakly magnetic neutron stars during thermonuclear flashes and in quiescence with future missions such as the International X-ray Observatory.

In this work we derive the analytical solution of the geodesic equations of Gödel’s universe for both particles and light in a special set of coordinates, which reveals the physical properties of this spacetime in a very transparent way. We also recapitulate the equations of isometric transport for points and derive the solution for Gödel’s universe. The equations of isometric transport for vectors are introduced and solved. We utilize these results to transform different classes of curves along Killing vector fields. In particular, we generate nontrivial closed timelike curves from circular closed timelike curves. The results can serve as a starting point for egocentric visualizations in the Gödel universe.

We determine the first independent part of the $g^6$ coefficient in the weak coupling expansion of the QCD pressure at high temperatures, the one proportional to the maximal power of the number of quark flavors $N_{\mathrm{f}}$. In addition to introducing and developing computational methods that can be used in evaluating other parts of the expansion, our calculation provides a result that becomes dominant in the limit of large $N_{\mathrm{f}}$ and a fixed effective coupling $g_{\mathrm{eff}}^2\equiv g^2{N}_{\mathrm{f}}/2$.

We construct a model of an unparticle sector consisting of a supersymmetric $SU(N)$ gauge theory with the number of flavors in the Seiberg conformal window. We couple this sector to the minimal supersymmetric standard model via heavy messengers. The resulting low energy theory has a Higgs coupling to unparticles. The Higgs vev drives the hidden Seiberg sector to a new conformal fixed point. The coupling to the Higgs mediates supersymmetry breaking to the Seiberg sector, and breaks conformal invariance at a lower scale. The low energy theory contains light stable and metastable mesons. Higgs decay into this sector gives signatures which are similar to those of “hidden valley” models. Decays of the lightest superpartner of standard model particles into the hidden sector reveal potentially observable unparticle kinematics.

We combine the analyses for flavor changing neutral current processes and dark matter solutions in minimal-type supersymmetric grand unified theory models, SO(10) and SU(5), with a large $B_s\mathrm{\text{−}}{\overline{B}}_s$ mixing phase and large $\tan \beta$. For large $\tan \beta$, the double-penguin diagram dominates the supersymmetry contribution to the $B_s\mathrm{\text{−}}{\overline{B}}_s$ mixing amplitude. Also, the $\mathrm{Br}(B_s\to \mu \mu )$ constraint becomes important as it grows as ${tan}^6\beta$, although it can still be suppressed by a large pseudoscalar Higgs mass $m_A$. We investigate the correlation between $B_s\to \mu \mu$ and the dark matter direct detection cross section through their dependence on $m_A$. In the minimal-type of SU(5) with type I seesaw, the large mixing in neutrino Dirac couplings results in a large lepton flavor violating decay process $\tau \to \mu \gamma$, which in turn sets the upper bound on $m_A$. In the SO(10) case, the large mixing can be chosen to be in the Majorana couplings instead, and the constraint from $\mathrm{Br}(\tau \to \mu \gamma )$ can be avoided. The heavy Higgs funnel region turns out to be an interesting possibility in both cases and the direct dark matter detection should be possible in the near future in these scenarios.

We study the effect of soft gluon emission in the hadroproduction of gluino-gluino and squark-antisquark pairs at the next-to-leading logarithmic accuracy within the framework of the minimal supersymmetric model. We present the calculation of the one-loop soft anomalous dimension matrices controlling the color evolution of the underlying hard-scattering processes. The numerical results for resummed cross sections for proton-proton collisions at the Large Hadron Collider are discussed in detail.

We perform a ${\chi }^2$ analysis of nuclear parton distribution functions (NPDFs) using neutral current charged-lepton (${\ell }^{\pm }A$) deeply inelastic scattering (DIS), and Drell-Yan data for several nuclear targets. The nuclear $A$ dependence of the NPDFs is extracted in a next-to-leading order fit. We compare the nuclear corrections factors ($F_2^{Fe}/F_2^D$) for this charged-lepton data with other results from the literature. In particular, we compare and contrast fits based upon the charged-lepton DIS data with those using neutrino-nucleon DIS data.

The potential for a precise measurement of the unitarity triangle angle $\gamma$ in future experiments from the decay $B^0\to D{K}^{*0}$ is well known. It has recently been suggested that the sensitivity can be significantly enhanced by analyzing the $B^0\to D{K}^{+}{\pi }^{-}$ Dalitz plot to extract amplitudes relative to those of the flavor-specific decay $B^0\to D_2^{*-}{K}^{+}$. An extension to this method which includes the case where the neutral $D$ meson is reconstructed in suppressed final states is presented. The sensitivity to $\gamma$ is estimated using this method and compared to that obtained using the $B^0\to D{K}^{*0}$ decay alone. Experimental effects, such as background contamination, are also considered. This approach appears to be a highly attractive addition to the family of methods that can be used to determine $\gamma$.

The big bounce (BB) transition within a flat Friedmann-Robertson-Walker model is analyzed in the setting of loop geometry underlying the loop cosmology. We solve the constraint of the theory at the classical level to identify physical phase space and find the Lie algebra of the Dirac observables. We express energy density of matter and geometrical functions in terms of the observables. It is the modification of classical theory by the loop geometry that is responsible for BB. The classical energy scale specific to BB depends on a parameter that should be fixed either by cosmological data or determined theoretically at quantum level, otherwise the energy scale stays unknown.

In this paper we propose a dark matter model and study aspects of its phenomenology. Our model is based on a new dark matter sector with a $U(1{)}^{\prime }$ gauge symmetry plus a discrete symmetry added to the standard model of particle physics. The new fields of the dark matter sector have no hadronic charges and couple only to leptons. Our model cannot only give rise to the observed neutrino mass hierarchy, but can also generate the baryon number asymmetry via nonthermal leptogenesis. The breaking of the new $U(1{)}^{\prime }$ symmetry produces cosmic strings. The dark matter particles are produced nonthermally from cosmic string loop decay which allows one to obtain sufficiently large annihilation cross sections to explain the observed cosmic ray positron and electron fluxes recently measured by the PAMELA, ATIC, PPB-BETS, Fermi-LAT, and HESS experiments while maintaining the required overall dark matter energy density. The high velocity of the dark matter particles from cosmic string loop decay leads to a low phase space density and thus to a dark matter profile with a constant density core in contrast to what happens in a scenario with thermally produced cold dark matter where the density keeps rising towards the center. As a result, the flux of $\gamma$ rays radiated from the final leptonic states of dark matter annihilation from the Galactic center is suppressed and satisfies the constraints from the HESS $\gamma$-ray observations.

Although gauge-boson propagators in asymptotically-free gauge theories satisfy a dispersion relation, they do not satisfy the Källen-Lehmann (KL) representation because the spectral function changes sign. We argue that this is a simple consequence of asymptotic freedom. On the basis of the QED-like Ward identities of the pinch technique (PT) we claim that the product of the coupling $g^2$ and the scalar part $\widehat{d}(q^2)$ of the PT propagator, which is both gauge invariant and renormalization-group invariant, can be factored into the product of the running charge ${\overline{g}}^2(q^2)$ and a term $\widehat{H}(q^2)$ both of which satisfy the KL representation although their product does not. We show that this behavior is consistent with some simple analytic models that mimic the gauge-invariant PT Schwinger-Dyson equations (SDE), provided that the dynamic gauge-boson mass is sufficiently large. The PT SDEs do not depend directly on the PT propagator through $\widehat{d}$ but only through $\widehat{H}$.

The cosmic ray interaction event generator Sibyll is widely used in extensive air shower simulations. We describe in detail the properties of Sibyll 2.1 and the differences with the original version 1.7. The major structural improvements are the possibility to have multiple soft interactions, introduction of new parton density functions, and an improved treatment of diffraction. Sibyll 2.1 gives better agreement with fixed target and collider data, especially for the inelastic cross sections and multiplicities of secondary particles. Shortcomings and suggestions for future improvements are also discussed.

We compute the next-to-leading order QCD corrections to the production of $W$ bosons in association with three jets at the Tevatron in the leading color approximation, which we define by considering the number of colors and the number of light flavors as being of the same order of magnitude. The theoretical uncertainty in the next-to-leading order prediction for the cross section is of the order of 15%–25% which is a significant improvement compared to the leading order result.

We investigate the weak nonleptonic decays of ${\Lambda }_c^{+}$, ${\Xi }_c^{+}$, and ${\Xi }_c^0$ into the octet baryons ($J^P=1/2^{+}$) and axial-vector mesons ($J^P=1^{+}$) employing the factorization scheme for $W$-emission diagrams and the pole model for $W$-exchange contributions. Determining the baryon-baryon transition form factors in the nonrelativistic quark model and incorporating the constraints of heavy quark symmetry, we predict their branching ratios and asymmetry parameters.