A quantization of unimodular gravity is described, which results in a quantum effective action which is also unimodular, ie a function of a metric with fixed determinant. A consequence is that contributions to the energy-momentum tensor of the form of $g_{ab}C$, where $C$ is a spacetime constant, whether classical or quantum, are not sources of curvature in the equations of motion derived from the quantum effective action. This solves the first cosmological constant problem, which is suppressing the enormous contributions to the cosmological constant coming from quantum corrections. We discuss several forms of unimodular gravity and put two of them, including one proposed by Henneaux and Teitelboim, in constrained Hamiltonian form. The path integral is constructed from the latter. Furthermore, the second cosmological constant problem, which is why the measured value is so small, is also addressed by this theory. We argue that a mechanism first proposed by Ng and van Dam for suppressing the cosmological constant by quantum effects obtains at the semiclassical level.

Marginal Lemaitre-Tolman-Bondi (LTB) models with corrections from loop quantum gravity have recently been studied with an emphasis on potential singularity resolution. This paper corroborates and extends the analysis in two regards: (i) the whole class of LTB models, including nonmarginal ones, is considered, and (ii) an alternative procedure to derive anomaly-free models is presented which first implements anomaly freedom in spherical symmetry and then the LTB conditions rather than the other way around. While the two methods give slightly different equations of motion, not altogether surprisingly given the ubiquitous sprawl of quantization ambiguities, final conclusions remain unchanged: compared to quantizations of homogeneous models, bounces seem to appear less easily in inhomogeneous situations, and even the existence of homogeneous solutions as special cases in inhomogeneous models may be precluded by quantum effects. However, compared to marginal models, bouncing solutions seem more likely with nonmarginal models.

Annihilation of cosmologically distributed dark matter is predicted to produce a potentially observable flux of high energy photons. This signal is predicted to be virtually uniform on the sky but, in order to be identified, must be extracted from various galactic and extragalactic backgrounds. We consider three techniques for extracting this signal from the backgrounds: spectral discrimination, angular discrimination, and distribution discrimination. We analyze the first two of these with the Fisher matrix formalism to obtain projections for constraints from the Fermi satellite. The third technique exploits the fact that the number of photons from extragalactic blazars is drawn from a distribution which is far from Poisson. Using a toy model, we show that knowledge of this distribution enhances one’s ability to extract the dark matter signal, while ignorance of it can lead to the introduction of a large systematic error.

The DGP braneworld scenario explains accelerated expansion of the Universe via leakage of gravity to extra dimensions without any need for dark energy. We study the behavior of homogeneous and anisotropic cosmologies on a warped DGP brane with perfect fluid as a matter source. Taking a conformally flat bulk, we obtain the general solutions of the field equations in an exact parametric form for Bianchi type I space-time with a pressureless fluid. Finally, the behavior of the observationally important parameters like shear, anisotropy, and the deceleration parameter is considered in detail. We find that isotropization can proceed slower in the warped DGP model than the generalized Randall-Sundrum II model.

We consider the hypothesis that dark matter (DM) has tree-level interactions only with leptons. Such a framework, where DM recoils against electrons bound in atoms, has been proposed as an explanation for the annually modulated scintillation signal in DAMA/LIBRA data versus the absence of a signal for nuclear recoils in experiments like CDMS or XENON10. However, even in such a leptophilic DM scenario there are loop-induced DM-hadron interactions, where photons emitted from virtual leptons couple to the charge of a nucleus. Using a general effective field theory approach we show that, if such an interaction is induced at one- or two-loop level, then DM-nucleus scattering dominates over DM-electron scattering. This is because the latter is suppressed by the bound state wave function. One obtains a situation similar to standard DM-nucleus scattering analyses with considerable tension between the results of DAMA and CDMS/XENON10. This conclusion does not apply in the case of pseudoscalar or axial-vector coupling between DM and leptons, where the loop diagrams vanish. In this case the explanation of the DAMA signal in terms of DM-electron scattering is strongly disfavored by the spectral shape of the signal. Furthermore, if DM can annihilate into neutrinos or tau leptons, the required cross sections are excluded by many orders of magnitude using the Super-Kamiokande bound on neutrinos from DM annihilations in the Sun.

The cosmic microwave background (CMB) bispectrum of the temperature anisotropies induced by a network of cosmic strings is derived for small angular scales, under the assumption that the principal cause of temperature fluctuations is the Gott-Kaiser-Stebbins effect. We provide analytical expressions for all isosceles triangle configurations in Fourier space. Their overall amplitude is amplified as the inverse cube of the angle and diverges for flat triangles. The isosceles configurations generically lead to a negative bispectrum with a power-law decay ${\ell }^{-6}$ for large multipole $\ell$. However, collapsed triangles are found to be associated with a positive bispectrum whereas the squeezed triangles still exhibit negative values. We then compare our analytical estimates to a direct computation of the bispectrum from a set of 300 statistically independent temperature maps obtained from Nambu-Goto cosmic string simulations in a Friedmann-Lemaître-Robertson-Walker universe. We find good agreement for the overall amplitude, the power-law behavior, and the angle dependency of the various triangle configurations. At $\ell \sim 500$ the cosmic string Gott-Kaiser-Stebbins effect contributes approximately the same equilateral CMB bispectrum amplitude as an inflationary model with $|f_{\mathrm{NL}}^{\mathrm{loc}}|\simeq {10}^3$, if the strings contribute about 10% of the temperature power spectrum at $\ell =10$. Current bounds on $f_{\mathrm{NL}}$ are not derived using cosmic string bispectrum templates, and so our $f_{\mathrm{NL}}$ estimate cannot be used to derive bounds on strings. However it does suggest that string bispectrum templates should be included in the search of CMB non-Gaussianities.

The primordial fluctuation spectrum is reconstructed from the five-year Wilkinson Microwave Anisotropy Probe data of the cosmic microwave background anisotropy. We divide the wave number space in the range of $1.23\times {10}^{-3}{\mathrm{Mpc}}^{-1}\lesssim k\lesssim 2.76\times {10}^{-2}{\mathrm{Mpc}}^{-1}$ into about 50 bins, and derive probability distributions of fluctuation amplitudes on the respective scales using Monte Carlo simulations. Although the reconstructed spectrum is basically consistent with a power-law spectrum, we find a hint of fine structure at $k\approx 0.002{\mathrm{Mpc}}^{-1}$ and $0.009{\mathrm{Mpc}}^{-1}$. The former is observed only in the temperature anisotropy, while the latter is both in the temperature and polarization anisotropies. The significance of these features are discussed, and it is shown that the deviation from a power-law spectrum at $k\approx 0.009{\mathrm{Mpc}}^{-1}$ is at $2.8\sigma$ level.

The quark’s behavior while influenced by a strong stochastic gluon field is analyzed. An approximate procedure for calculating the effective Hamiltonian is developed and the corresponding ground state within the Hartree-Fock-Bogolyubov approach is found. The comparative analysis of various Hamiltonian models is given and transition to the chiral limit in the Keldysh model is discussed in detail.

We study the stability of the Higgs potential in the framework of the effective Lagrangian beyond the minimal supersymmetric standard model (MSSM). While the leading nonrenormalizable operators can shift the Higgs boson mass above the experimental bound, they also tend to render the scalar potential unbounded from below. The destabilization is correlated with the Higgs mass increase, so that if quantum corrections are small the problem is severe. We show that a supersymmetric subleading correction stabilizes the potential within the domain of validity of the effective theory. Constraints on MSSM parameters as well as on higher dimensional operators are derived, ensuring that our vacuum has a lifetime longer than the present age of the Universe. In addition we show that when effective operators are responsible for evading the LEP bound, stability constraints imply an upper bound on the scale of new physics in the few TeV range.

We investigate flavor violation mediated by Higgs bosons and supersymmetric particles in a predictive class of models based on the non-Abelian flavor symmetry $Q_6$. These models, which aim to reduce the number of parameters of the fermion sector and to solve the flavor changing problems of generic supersymmetry (SUSY) setup, assume three families of Higgs bosons and spontaneous or soft violation of $CP$ symmetry. Tree-level contributions to meson-antimeson mixings mediated by Higgs bosons are shown to be within experimental limits for Higgs masses in the (1–5) TeV range. Calculable flavor violation induced by SUSY loops are analyzed for meson mixing and lepton decays and found to be consistent with data. Significant new SUSY contributions arise in $B_s–{\overline{B}}_s$ mixing, but nonstandard $CP$ violation is suppressed. A simple solution to the SUSY $CP$ problem is found, which requires light Higgsinos.

We argue that effective field theories compatible with the idea of cosmological supersymmetry breaking (CSB) can have no supersymmetric vacuum states in the $M_P\to \infty$ limit. We introduce a revised version of the pyramid scheme, which satisfies this criterion. Combining the criteria for CSB with results of Nelson and Seiberg, any such Lagrangian is nongeneric, but we argue that this is plausible in the context of CSB, where R-violating terms in the Lagrangian come from interactions with the horizon, rather than integrating out short distance degrees of freedom. We also point out a Landau pole in the hidden sector gauge group of the pyramid scheme, and propose a mechanism for avoiding it.

The PAMELA positron excess is analyzed within the framework of nonuniversal supergravity (SUGRA) models with an extended $U(1{)}^n$ gauge symmetry in the hidden sector leading to neutralino dark matter with either a mixed Higgsino-wino lightest $R$-parity odd supersymmetric particle (LSP) or an essentially pure wino-dominated LSP. The Higgsino-wino LSP can produce the observed PAMELA positron excess and satisfy relic density constraints in the extended class of models due to a near degeneracy of the mass spectrum of the extended neutralino sector with the LSP mass. The simultaneous satisfaction of the WMAP relic density data and the PAMELA data is accomplished through a coannihilation mechanism ($B_{\mathrm{Co}}-\mathrm{\text{mechanism}}$), and leads to predictions of a neutralino and a chargino in the mass range (180–200) GeV as well as low-lying sparticles accessible at colliders. We show that the models are consistent with the antiproton constraints from PAMELA as well as the photon flux data from EGRET and FERMI-LAT. Predictions for the scalar neutralino-proton cross section relevant for the direct detection of dark matter are also discussed and signatures at the LHC for these PAMELA inspired models are analyzed. It is shown that the mixed Higgsino-wino LSP model will be discoverable with as little as $1{\mathrm{fb}}^{-1}$ of data and is thus a prime candidate for discovery in the low luminosity runs at the LHC.

Properties of the charmoniumlike state $X(3872)$ are investigated and its nature is discussed as based on the existing experimental data. In particular, we analyze the new data from Belle and BABAR Collaborations and argue that, while the BABAR data prefer the dynamically generated virtual state in the $D{\overline{D}}^{*}$ system, the new Belle data clearly indicate a sizable $c\overline{c}$ $2^3{P}_1$ component in the $X$ wave function.

We consider a novel class of hard branching hadronic processes $a+b\to c+d+e$, where hadrons $c$ and $d$ have large and nearly opposite transverse momenta and large invariant energy, which is a finite fraction of the total invariant energy. We use color transparency logic to argue that these processes can be used to study quark generalized parton distributions (GPDs) for baryons and mesons in hadron collisions, hence complementing and adding to the studies of GPDs in the exclusive deep inelastic scattering processes. We propose that a number of GPDs can be investigated in hadron facilities such as Japan Proton Accelerator Research Complex facility and Gesellschaft für Schwerionenforschung -Facility for Antiproton and Ion Research project. In this work, the GPDs for the nucleon and for the $N\to \Delta$ transition are studied in the reaction $N+N\to N+\pi +B$, where $N$, $\pi$, and $B$ are a nucleon, a pion, and a baryon (nucleon or $\Delta$), respectively, with a large momentum transfer between $B$ (or $\pi$) and the incident nucleon. In particular, the Efremov-Radyushkin-Brodsky-Lepage region of the GPDs can be measured in such exclusive reactions. We estimate the cross section of the processes $N+N\to N+\pi +B$ by using current models for relevant GPDs and information about large angle $\pi N$ reactions. We find that it will be feasible to measure these cross sections at the high-energy hadron facilities and to get novel information about the nucleon structure, for example, contributions of quark orbital angular momenta to the nucleon spin. The studies of $N\to \Delta$ transition GPDs could be valuable also for investigating electromagnetic properties of the transition.

Using a nonlocal chiral quark model with simple pole ansatz for the momentum dependence of the constituent quark mass and nonlocal currents satisfying Ward-Takahashi identities, we calculate pion-to-photon transition distribution amplitudes and relevant form factors. For vector amplitude we recover correct normalization fixed by the axial anomaly. We find that due to the nonlocality in the vector current, the value of the axial form factor at zero momentum transfer is lowered with respect to the vector form factor. Such behavior—consistent with experiment—is not seen in the local models. Where possible we compare our results to the experimental data.

We study the structures in cross sections and $R$ ratios concerning $e^{+}{e}^{-}$ annihilation reactions, for open-strangeness, open-charm, and open-beauty hadron-pair production, from the perspective of a recently developed production formalism. Special attention is paid to nonresonant contributions. Known, tentative, and yet unknown resonances are spotted, with estimates for their masses and widths.

Using a first-order formulation for general relativity that assumes the independence between the metric and the connection of the background manifold, it is proved that new gauge symmetries of the theory are manifested on manifolds with harmonic curvature and with parallel Ricci tensor; these symmetries mimic those of a BF gauge field theory. Additionally, under the same assumption, connection flows are constructed on the space of connections, which mimic the conventional Ricci flows on the space of metrics; at the end the two dynamical equations constitute a system of coupled evolutions for geometries, which tend to distribute both structures uniformly and consistently over the manifold.

We consider theories where the standard model (SM) neutrinos acquire masses through the seesaw mechanism at the weak scale. We show that in such a scenario, the requirement that any preexisting baryon asymmetry, regardless of its origin, not be washed out leads to correlations between the pattern of SM neutrino masses and the spectrum of new particles at the weak scale, leading to definite predictions for the LHC. For type I seesaw models with a TeV scale $Z^{\prime }$ coupled to SM neutrinos, we find that for a normal neutrino mass hierarchy, at least one of the right-handed neutrinos must be “electrophobic,” decaying with a strong preference into final states with muons and tauons rather than electrons. For inverted or quasidegenerate mass patterns, on the other hand, we find upper bounds on the mass of at least one right-handed neutrino. In particular, for an inverted mass hierarchy, this bound is 1 TeV, while the corresponding upper limit in the quasidegenerate case is 300 GeV. Similar results hold in type III seesaw models, albeit with somewhat more stringent bounds. For the type II seesaw case with a weak-scale $SU(2)$ triplet Higgs, we again find that an interesting range of Higgs triplet masses is disallowed by these considerations.

Using the AdS/CFT correspondence, we compute the radiative energy loss of a slowly decelerating heavy quark with mass $M$ moving through a supersymmetric Yang-Mills plasma at temperature $T$ and large ’t Hooft coupling $\lambda$. The calculation is carried out in terms of perturbations in $\sqrt{\lambda }T/M$, and the rate of the energy loss is computed up to second order. We explain the physical meaning of each correction and estimate the thermalization time of a heavy quark moving in a strongly-coupled plasma.

We lay the foundations for the construction of analytic expressions for Fourier-domain gravitational waveforms produced by eccentric, inspiraling compact binaries in a post-circular or small-eccentricity approximation. The time-dependent, “plus” and “cross” polarizations are expanded in Bessel functions, which are then self-consistently reexpanded in a power series about zero initial eccentricity to eighth order. The stationary-phase approximation is then employed to obtain explicit analytic expressions for the Fourier transform of the post-circular expanded, time-domain signal. We exemplify this framework by considering Newtonian-accurate waveforms, which in the post-circular scheme give rise to higher harmonics of the orbital phase and to amplitude corrections of the Fourier-domain waveform. Such higher harmonics lead to an effective increase in the inspiral mass reach of a detector as a function of the binary’s eccentricity $e_0$ at the time when the binary enters the detector sensitivity band. Using the largest initial eccentricity allowed by our approximations ($e_0<0.4$), the mass reach is found to be enhanced up to factors of approximately 5 relative to that of circular binaries for Advanced LIGO, LISA, and the proposed Einstein Telescope at a signal-to-noise ratio of ten. A post-Newtonian generalization of the post-circular scheme is also discussed, which holds the promise to provide “ready-to-use” Fourier-domain waveforms for data analysis of eccentric inspirals.