In split-supersymmetry scenarios the possibility of having a very heavy gravitino opens the door to alleviate or completely solve the worrisome “gravitino problem” in the context of supersymmetric baryogenesis models. Here we assume that the gravitino may indeed be heavy and that Majorana masses for neutrinos are forbidden as well as direct Higgs Yukawa couplings between left- and right-handed neutrinos. We investigate the viability of the mechansim known as Dirac leptogenesis (or neutrinogenesis), both in solving the baryogenesis puzzle and explaining the observed neutrino sector phenomenology. To successfully address these issues, the scenario requires the introduction of at least two new heavy fields. If a hierarchy among these new fields is introduced, and some reasonable stipulations are made on the couplings that appear in the superpotential, it becomes a generic feature to obtain the observed large lepton mixing angles. We show that in this case, it is possible simultaneously to obtain both the correct neutrino phenomenology and enough baryon number, making thermal Dirac neutrinogenesis viable. However, due to cosmological constraints, its ability to satisfy these constraints depends nontrivially on model parameters of the overall theory, particularly the gravitino mass. Split supersymmetry with ${10}^5\mathrm{GeV}\lesssim m_{3/2}\lesssim {10}^{10}\mathrm{GeV}$ emerges as a “natural habitat” for thermal Dirac neutrinogenesis.

We obtain the spectrum of gamma-ray emissions from the moduli whose decay into $e^{+}{e}^{-}$ accounts for the 511 keV line observed by SPI/INTERGRAL. The moduli emit gamma rays through internal bremsstrahlung, and also decay directly into two gammas via tree and/or one-loop diagrams. We show that the internal bremsstahlung constrains the mass of the moduli below $\sim 40\mathrm{MeV}$ model-independently. On the other hand, the flux of two gammas directly decayed from the moduli through one-loop diagrams will exceed the observed galactic diffuse gamma-ray background if the moduli mass exceeds $\sim 20\mathrm{MeV}$ in the typical situation. Moreover, forthcoming analysis of SPI data in the range of 1–8 MeV may detect the line emisson with the energy half the moduli mass in the near future, which confirms the decaying moduli scenario.

We construct a generalized formalism for group field theories, in which the domain of the field is extended to include additional proper time variables, as well as their conjugate mass variables. This formalism allows for different types of quantum gravity transition amplitudes in perturbative expansion, and we show how both causal spin foam models and the usual a-causal ones can be derived from it, within a sum over triangulations of all topologies. We also highlight the relation of the so-derived causal transition amplitudes with simplicial gravity actions.

By choosing two typical input parameter points in the minimal supergravity (mSUGRA) model and using the QCD factorization (QCDF) approach, we studied the supersymmetric (SUSY) effects to the $CP$ violation of the two-body charmless hadronic $B$ meson decays. We found that though the SUSY contributions can give large corrections to the $CP$ asymmetries for some decay channels, they could not be distinguished experimentally from the standard model (SM) values because of the large theoretical errors dominated by the annihilation contributions in the QCDF approach.

We study the mass spectra, production, and decay properties of the lightest supersymmetric $CP$-even and $CP$-odd Higgs bosons in models with spontaneously broken $R$ parity. We compare the resulting mass spectra with expectations of the minimal supersymmetric standard model (MSSM), stressing that the model obeys the upper bound on the lightest $CP$-even Higgs boson mass. We discuss how the presence of the additional scalar singlet states affects the Higgs production cross sections, both for the Bjorken process and the “associated production.” The main phenomenological novelty with respect to the MSSM comes from the fact that the spontaneous breaking of lepton number leads to the existence of the majoron, denoted $J$, which opens new decay channels for supersymmetric Higgs bosons. We find that the invisible decays of $CP$-even Higgses can be dominant, while those of the $CP$-odd bosons may also be sizable.

We calculate the 1-loop renormalization of the fermion self-energy, all local fermion bilinears, as well as a set of extended bilinears which form a basis corresponding to moments of the parton distribution functions. We use the overlap action for fermions and Symanzik improved action for gluons. Our results are presented as a function of the overlap parameter $\rho$ and the parameters entering the Symanzik action.

We argue that at sufficiently small Bjorken $x$ where pQCD amplitudes rapidly increase with energy and violate probability conservation the shadowing effects in the single-scale small $x$ hard QCD processes can be described by an effective quantum field theory of interacting quasiparticles—perturbative QCD ladders. We find, within the WKB approximation, that the smallness of the QCD coupling constant ensures the hierarchy among many-quasiparticle interactions evaluated within the physical vacuum and, in particular, the dominance in the Lagrangian of the triple quasiparticle interaction. It is explained that the effective field theory considered near the perturbative QCD vacuum contains a tachyon relevant for the divergency of the perturbative QCD series at sufficiently small $x$. We solve the equations of motion of the effective field theory within the WKB approximation and find the physical vacuum and the transitions between the false (perturbative) and physical vacua. Classical solutions which dominate transitions between the false and physical vacua are kinks that cannot be decomposed into perturbative series over the powers of ${\alpha }_s$. These kinks lead to color inflation and the Bose-Einstein condensation of quasiparticles. The account of the quantum fluctuations around the WKB solution reveals the appearance of the “massless” particles—phonons. It is explained that phonons are relevant for the black disk behavior of cross sections of small $x$ processes. The Bose-Einstein condensation of the ladders produces a color network occupying a “macroscopic” longitudinal volume. We discuss briefly the possible detection of new QCD effects. We outline albeit briefly the relationship between the small $x$ hard QCD processes and the coherent critical phenomena.

In the present paper, we reexamine the moduli stabilization problem of Type IIB orientifolds with one complex structure modulus in a modified two-step procedure. The full superpotential including both the 3-form flux contributions and the nonperturbative corrections is used throughout the stabilization procedure. The F-term potential is simplified by using one optimization condition to integrate out the dilaton field in the first stage. By analyzing the Hessian determinants we establish some criterion inequalities with which one can easily judge whether a Type IIB orientifold with one complex structure modulus could have a metastable deSitter vacuum without the inclusion of the uplifting energies.

Compactifying the $A_1$ version of (2,0) theory on a circle gives rise to five-dimensional, maximally supersymmetric Yang-Mills theory. In the Coulomb branch, where the $\mathrm{SU}(2)$ gauge group is spontaneously broken to a U(1) subgroup, the degrees of freedom are constituted by one massless and two massive vector multiplets. Because of the relation to the six-dimensional (2,0) theory, we are then interested in scattering processes where both the in-state and the out-state consist of one massless and one massive particle. We show that the corresponding part of the $S$ matrix is determined by the symmetries of the theory up to a single unknown function, which depends on the energy and mass of the incoming particles, together with the scattering angle. Performing a straightforward scattering calculation by means of Feynman diagrams, this function is determined to leading order in a low-energy approximation. The result is strikingly simple, and it coincides exactly with the corresponding function in the (2,0) theory.

The possibility of radiative effects induced by the Lorentz and $CPT$ noninvariant interaction term for fermions in the standard model extension is investigated. In particular, electron-positron photo production and photon emission by electrons and positrons are studied. The rates of these processes are calculated in the Furry picture. It is demonstrated that the rates obtained in the framework of the model adopted strongly depend on the polarization states of the particles involved. As a result, ultrarelativistic particles produced should occupy states with a preferred spin orientation, i.e., photons have the sign of polarization opposite to the sign of the effective potential, while charged particles are preferably in the state with the helicity coinciding with the sign of the effective potential. This leads to evident spatial asymmetries which may have certain consequences observable at high energy accelerators, and in astrophysical and cosmological studies.

We investigate models described by real scalar fields, searching for defect structures in the presence of interactions which explicitly violate Lorentz and $CPT$ symmetries. We first deal with a single field, and we investigate a class of models which supports traveling waves that violate Lorentz invariance. This scenario is then generalized to the case of two (or more) real scalar fields. In the case of two fields, in particular, we introduce another class of models, which supports topological structures that attain a Bogomol’nyi bound, although violating both Lorentz and $CPT$ symmetries. An example is considered, for which we construct the Bogomol’nyi bound and find some explicit solutions. We show that violation of both Lorentz and $CPT$ symmetries induces the appearance of an asymmetry between defects and antidefects, including the presence of linearly stable solutions with negative energy density in their outer side.

The effects of light propagation in constant magnetic and electric backgrounds are considered in the framework of the effective action approach. We use the exact analytic series representation for the one-loop effective action of QED and apply it to the birefringence effect. Analytical results for the light velocity modes are obtained for the weak and the strong field regime. We present asymptotic formulas for the light velocity modes for the ultrastrong magnetic field which can be realized in some neutron stars.

Computational techniques which establish the stability of an evolution-boundary algorithm for a model wave equation with shift are incorporated into a well-posed version of the initial-boundary value problem for gravitational theory in harmonic coordinates. The resulting algorithm is implemented as a 3-dimensional numerical code which we demonstrate to provide stable, convergent Cauchy evolution in gauge wave and shifted gauge wave testbeds. Code performance is compared for Dirichlet, Neumann, and Sommerfeld boundary conditions and for boundary conditions which explicitly incorporate constraint preservation. The results are used to assess strategies for obtaining physically realistic boundary data by means of Cauchy-characteristic matching.

We analyze the fate of excitations in regions of closed string tachyon condensate, a question crucial for understanding unitarity in a class of black holes in string theory. First we introduce a simple new example of quasilocal tachyon condensation in a globally stable AdS/CFT background, and review tachyons’ appearance in black hole physics. Then we calculate forces on particles and fields in a tachyon phase using a field theoretic model with spatially localized exponentially growing time-dependent masses. This model reveals two features, both supporting unitary evolution in the bulk of spacetime. First, the growing energy of fields sourced by sets of (real and virtual) particles in the tachyon phase yields outward forces on them, leaving behind only combinations which do not source any fields. Secondly, requiring the consistency of perturbative string theory imposes cancellation of a BRST anomaly, which also yields a restricted set of states. Each of these effects supports the notion of a black hole final state arising from string-theoretic dynamics replacing the black hole singularity.

We analyze the observational and theoretical constraints on “Einstein-aether theory,” a generally covariant theory of gravity coupled to a dynamical, unit, timelike vector field that breaks local Lorentz symmetry. The results of a computation of the remaining post-Newtonian parameters are reported. These are combined with other results to determine the joint post-Newtonian, vacuum-Čerenkov, nucleosynthesis, stability, and positive-energy constraints. All of these constraints are satisfied by parameters in a large two-dimensional region in the four-dimensional parameter space defining the theory.

In this paper we show that by considering a universe dominated by two interacting components a superaccelerated expansion can be obtained from a decelerated one by applying a dual transformation that leaves the Einstein’s field equations invariant.

Gravitational lensing can be used to directly constrain the projected density profile of galaxy clusters. We discuss possible future constraints using lensing of the cosmic microwave background (CMB) temperature and polarization, and compare to results from using galaxy weak lensing. We model the moving lens and kinetic Sunyaev-Zel’dovich signals that confuse the temperature CMB lensing when cluster velocities and angular momenta are unknown, and show how they degrade parameter constraints. The CMB polarization cluster lensing signal is $\sim 1\mu \mathrm{K}$ for massive clusters and challenging to detect; however it should be significantly cleaner than the temperature signal and may provide the most robust constraints at low noise levels. Galaxy lensing is likely to be much better for constraining cluster masses at low redshift, but for clusters at redshift $z\gtrsim 1$ future CMB lensing observations may be able to do better.

Motivated by the recent extraction of the helicity amplitudes for the $D^{+}\to {\overline{K}}^{*0}\mu {\nu }_{\mu }$ decay, done by the FOCUS collaboration, we determine helicity amplitudes for the $D^{+}\to {\overline{K}}^{*0}l{\nu }_l$, $D^{+}\to {\rho }^{0}l{\nu }_l$ and $D_s^{+}\to \varphi l{\nu }_l$ semileptonic decays using the knowledge of the relevant form factors. The vector and axial form factors for $D\to Vl{\nu }_l$ decays are parametrized by including contributions of charm meson resonances and using the HQET and SCET limits. In the case that the vector form factor receives contributions from two poles while axial form factors are dominated by a single pole for $D^{+}\to {\overline{K}}^{*0}l{\nu }_l$, we obtain better agreement with the experimental result then when all of them are dominated by single poles.

We investigate the TeV-scale stringy signals of the four-fermion scattering at the electron-positron collider with the center-of-mass energy 500–1000 GeV. The nature of the stringy couplings leads to distinguishable asymmetries comparing to the other new physics models. Specifically, the stringy states in the four-fermion scattering at the leading-order corrections are of spin-1 and 2 with the chiral couplings inherited from the gauge bosons identified as the zeroth-mode string states. The angular left-right, forward-backward, center-edge asymmetries, and the corresponding polarized-beam asymmetries are investigated. The low-energy stringy corrections are compared to the ones induced by the Kaluza-Klein (KK) gravitons. The angular left-right asymmetry of the scattering with the final states of $u$ and $d$-type quarks, namely $c$ and $b$, shows significant deviations from the standard model values. The center-edge and forward-backward asymmetries for all final-states fermions also show significant deviations from the corresponding standard model values. The differences between the signatures induced by the stringy corrections and the KK gravitons are appreciable in both angular left-right and forward-backward asymmetries.

Using Taylor expansions of the pressure obtained previously in studies of 2-flavor QCD at nonzero chemical potential we calculate expansion coefficients for the energy and entropy densities up to $\mathcal{O}({\mu }_q^6)$ in the quark chemical potential. We use these series in ${\mu }_q/T$ to determine lines of constant entropy per baryon number ($S/N_B$) that characterize the expansion of dense matter created in heavy ion collisions. In the high temperature regime these lines are found to be well approximated by lines of constant ${\mu }_q/T$. In the low temperature phase, however, the quark chemical potential is found to increase with decreasing temperature. This is in accordance with resonance gas model calculations. Along the lines of constant $S/N_B$ we calculate the energy density and pressure. Within the accuracy of our present analysis we find that the ratio $p/ϵ$ for $T>T_0$ as well as the softest point of the equation of state, $(p/ϵ{)}_{\min }\simeq 0.075$, show no significant dependence on $S/N_B$.