$K^0\to {\pi }^{-}{e}^{+}{\nu }_e{e}^{+}{e}^{-}$ decay rates are studied up to the next-to-leading order (${\mathcal{O}}^{(4)}$) in chiral perturbation theory. It is found that the ${\mathcal{O}}^{(4)}$ terms appreciably modify the shape of the invariant mass distribution of leptons ($M_{3e\nu }$) and the energy spectrum of neutrinos.

We investigate, within the type I seesaw framework, the physical implications of zero textures in the Yukawa couplings which generate the neutrino Dirac mass matrix $m_D$. It is shown that four is the maximal number of texture zeros compatible with the observed leptonic mixing and the assumption that no neutrino mass vanishes. We classify all allowed four-zero textures of $m_D$ into two categories with three classes each. We show that the different classes, in general, admit $CP$ violation both at low and high energies. We further present the constraints obtained for low energy physics in each case. The role of these zero textures in establishing a connection between leptogenesis and low energy data is analyzed in detail. It is shown that it is possible in all cases to completely specify the parameters relevant for leptogenesis in terms of light neutrino masses and leptonic mixing together with the unknown heavy neutrino masses.

Recently, Maldacena and Swanson suggested a new limit of string theory on the ${\mathrm{AdS}}_5\times S^5$ background, the so-called near flat space limit. The resulting reduced theory interpolates between the $pp$-wave limit and giant magnon-type string solutions. It was shown that the reduced model possesses many features of the original theory. On the other hand, theories with less supersymmetry are of great importance for the string/gauge theory correspondence. In this paper we study the near flat limit reduction of string theory on the Maldacena-Nunez background, which is dual to $\mathcal{N}=1$ Yang-Mills theory. The reduced model interpolates between the $pp$-wave limit and a certain magnon-type subsector of the theory. The similarity of the structures of the reduced model obtained here and that by Maldacena and Swanson indicates the possibility of existence of integrable subsectors of strings on the Maldacena-Nunez background.

Based on the trace anomaly for the energy-momentum tensor, an effective theory for the thermodynamics of the deconfining phase, and by assuming the asymptotic behavior to be determined by one-loop perturbation theory, we compute the nonperturbative beta function for the fundamental coupling $g$ in SU(2) and SU(3) Yang-Mills theory. With increasing temperature we observe a very rapid approach to the perturbative running. The Landau pole is nonperturbatively screened.

We consider gauge vortices in symmetry-breaking models with a noncanonical kinetic term. This work extends our previous study on global topological $k$-defects [Phys. Rev. D 74, 085004 (2006), including a gauge field. The model consists of a scalar field with a noncanonical kinetic term, while for the gauge field the standard form of its kinetic term is preserved. Topological defects arising in such models, $k$-vortices, may have quite different properties as compared to standard vortices. This happens because an additional dimensional parameter enters the Lagrangian for the considered model—a kinetic mass. We briefly discuss possible consequences for cosmology, in particular, the formation of cosmic strings during phase transitions in the early universe and their properties.

We generalize the effective point particle approach to black hole dynamics to include spin. In this approach, dissipative effects are captured by degrees of freedom localized on the worldline. The absorptive properties of the black hole are determined by correlation functions which can be matched with the graviton absorption cross section in the long wavelength approximation. For rotating black holes, superradiance is responsible for the leading contribution. The effective theory is then used to predict the power loss due to spin in the dynamics of nonrelativistic binary systems. An enhancement of three powers of the relative velocity is found with respect to the nonrotating case. Then we generalize the results to other types of constituents in the binary system, such as rotating neutron stars. Finally, we compute the power loss absorbed by a test spinning black hole in a given spacetime background.

We construct axially symmetric, rotating boson stars with positive and negative parity. Their flat space limits represent spinning $Q$-balls. $Q$-balls and boson stars exist only in a limited frequency range. The coupling to gravity gives rise to a spiral-like frequency dependence of the mass and charge of boson stars. We analyze the properties of these solutions. In particular, we discuss the presence of ergoregions in boson stars and determine their domains of existence.

The generalized Chaplygin gas, which interpolates between a high density relativistic era and a nonrelativistic matter phase, is a popular dark energy candidate. We consider a generalization of the Chaplygin gas model, by assuming the presence of a bulk viscous type dissipative term in the effective thermodynamic pressure of the gas. The dissipative effects are described by using the truncated Israel-Stewart model, with the bulk viscosity coefficient and the relaxation time functions of the energy density only. The corresponding cosmological dynamics of the bulk viscous Chaplygin gas dominated universe is considered in detail for a flat homogeneous isotropic Friedmann-Robertson-Walker geometry. For different values of the model parameters we consider the evolution of the cosmological parameters (scale factor, energy density, Hubble function, deceleration parameter, and luminosity distance, respectively), by using both analytical and numerical methods. In the large time limit the model describes an accelerating universe, with the effective negative pressure induced by the Chaplygin gas and the bulk viscous pressure driving the acceleration. The theoretical predictions of the luminosity distance of our model are compared with the observations of the type Ia supernovae. The model fits well the recent supernova data. From the fitting we determine both the equation of state of the Chaplygin gas, and the parameters characterizing the bulk viscosity. The evolution of the scalar field associated to the viscous Chaplygin fluid is also considered, and the corresponding potential is obtained. Hence the viscous Chaplygin gas model offers an effective dynamical possibility for replacing the cosmological constant, and for explaining the recent acceleration of the universe.

Highly relativistic jets are a key element of current gamma-ray burst models, where the jet kinetic energy is converted to radiation energy at optically thin shocks. High-energy neutrinos are also expected, from interactions of protons accelerated in the same shocks. Here we revisit the early evolution of a relativistic jet, while the jet is still inside the star, and investigate its neutrino emission. In particular we study propagation of mildly relativistic and ultrarelativistic jets through a type Ib progenitor, and follow reverse shocks as the jets cross the star. We show that protons can be accelerated to ${10}^4–{10}^5\mathrm{GeV}$ at reverse shocks, and efficiently produce mesons. The mesons experience significant cooling, suppressing subsequent neutrino emission. We show, however, that the neutrino yield from the reverse shock is still reasonably large, especially for low-luminosity and long-duration jets, where meson cooling is less severe. We discuss implications of our results in the context of neutrinos from choked jets, which are completely shock heated and do not break out of the star. From a choked jet with isotropic equivalent energy of ${10}^{53}\mathrm{erg}$ at 10 Mpc, we expect $\sim 20$ neutrino events at IceCube.

By analytic continuation to real $\theta$ of data obtained from numerical simulation at imaginary $\theta$ we study the Haldane conjecture and show that the O(3) nonlinear sigma model with a $\theta$ term in two dimensions becomes massless at $\theta =3.10(5)$. A modified cluster algorithm has been introduced to simulate the model with imaginary $\theta$. Two different definitions of the topological charge on the lattice have been used; one of them needs renormalization to match the continuum operator. Our work also offers a successful test for numerical methods based on analytic continuation.

The gluon-gluon-Higgs amplitude is investigated in the context of 5D models of gauge-Higgs unification. A simple algorithm allows one to include, in a fully analytical way, the contribution of the whole Kaluza-Klein tower of a 5D quark to the amplitude. This algorithm is applied to realistic models based on $SO(5)$ symmetry. Within the studied classes of models, the Higgs production cross section is always suppressed.

Traditional searches for supersymmetry (SUSY) at hadron colliders rely heavily on the presence of large missing transverse energy ($M{E}_T$) to reject background compared to signal. On the other hand, initial searches for new physics at the CERN LHC may not be able to rely on $M{E}_T$ due to a variety of detector calibration issues. We show that much of SUSY parameter space is accessible to discovery even without using $M{E}_T$, and with rather low integrated luminosities, $0.1–1{\mathrm{fb}}^{-1}$. A key role is played by isolated lepton multiplicity which arises from gluino and squark cascade decays. Requiring $\ge 3$ isolated leptons plus jets yields a high rate of background rejection compared to signal. We find an LHC reach in $m_{\tilde{g}}$ of about 700–750 GeV for just $0.1{\mathrm{fb}}^{-1}$ of integrated luminosity by requiring events with $\ge 4$ jets plus $\ge 3$ isolated leptons but without using $M{E}_T$. If a large enough event sample is assembled, then kinematic reconstruction of sparticle mass properties should be possible just as in the case where large missing $E_T$ is required. SUSY without $M{E}_T$ can also be seen in opposite-sign/same flavor dilepton plus jets events when a characteristic invariant mass edge stands out against background.

The final-state interaction in multichannel decay processes is systematically studied in the hadronic picture with application to $B$ decay in mind. Since the final-state interaction is intrinsically interwoven with the decay interaction in this case, no simple phase theorem like “Watson’s theorem” holds for experimentally observed final states. We first solve exactly the two-channel problem as a toy model in order to clarify the issues. The constraints of the two-channel approximation turns out to be too stringent for most $B$ decay modes, but realistic multichannel problems are too complex for useful quantitative analysis at present. To alleviate the stringent constraints of the two-body problem and to cope with complexity beyond it, we introduce a method of approximation that is applicable to the case where one prominent inelastic channel dominates over all others. We illustrate this approximation method with the amplitude of the decay $B\to K\pi$ fed by the intermediate states of a charmed-meson pair. Even with our approximation we need more accurate information of strong interactions than we have now. Nonetheless we are able to obtain some insight in the issue and draw useful conclusions on general features on the strong phases.

We propose a model for pentaquarks in an excited state in the flux tube picture. The pentaquark is assumed to be composed of two diquarks and an antiquark connected by a color flux tube with a junction. If the pentaquark is rotating rapidly, it is polarized into two clusters: one is a diquark and the other is an antiquark plus another diquark. Excited energy of this quasilinear system is calculated with the use of the WKB approximation. It is predicted that there exist quasistable excited pentaquarks: $1690\mathrm{MeV}(3/2^{+})$, $2000\mathrm{MeV}(5/2^{-})$, $2250\mathrm{MeV}(7/2^{+})$ etc., which decay mainly through three-body modes.

We investigate target mass effects in the unpolarized virtual photon structure functions $F_2^{\gamma }(x,Q^2,P^2)$ and $F_L^{\gamma }(x,Q^2,P^2)$ in perturbative QCD for the kinematical region ${\Lambda }^2\ll P^2\ll Q^2$, where $-Q^2(-P^2)$ is the mass squared of the probe (target) photon and $\Lambda$ is the QCD scale parameter. We obtain the Nachtmann moments for the structure functions and then, by inverting the moments, we get the expressions in closed form for $F_2^{\gamma }(x,Q^2,P^2)$ up to the next-to-next-to-leading order and for $F_L^{\gamma }(x,Q^2,P^2)$ up to the next-to-leading order, both of which include the target mass corrections. Numerical analysis exhibits that target mass effects appear at large $x$ and become sizable near $x_{\max }(=1/(1+\frac{P^2}{Q^2}))$, the maximal value of $x$, as the ratio $P^2/Q^2$ increases.

Theories with spontaneous local Lorentz and diffeomorphism violation contain massless Nambu-Goldstone modes, which arise as field excitations in the minimum of the symmetry-breaking potential. If the shape of the potential also allows excitations above the minimum, then an alternative gravitational Higgs mechanism can occur in which massive modes involving the metric appear. The origin and basic properties of the massive modes are addressed in the general context involving an arbitrary tensor vacuum value. Special attention is given to the case of bumblebee models, which are gravitationally coupled vector theories with spontaneous local Lorentz and diffeomorphism violation. Mode expansions are presented in both local and spacetime frames, revealing the Nambu-Goldstone and massive modes via decomposition of the metric and bumblebee fields, and the associated symmetry properties and gauge fixing are discussed. The class of bumblebee models with kinetic terms of the Maxwell form is used as a focus for more detailed study. The nature of the associated conservation laws and the interpretation as a candidate alternative to Einstein-Maxwell theory are investigated. Explicit examples involving smooth and Lagrange-multiplier potentials are studied to illustrate features of the massive modes, including their origin, nature, dispersion laws, and effects on gravitational interactions. In the weak static limit, the massive mode and Lagrange-multiplier fields are found to modify the Newton and Coulomb potentials. The nature and implications of these modifications are examined.

Indirect detection signals from dark matter annihilation are studied in the positron channel. We discuss in detail the positron propagation inside the galactic medium: we present novel solutions of the diffusion and propagation equations and we focus on the determination of the astrophysical uncertainties which affect the positron dark matter signal. We find dark matter scenarios and propagation models that nicely fit existing data on the positron fraction. Finally, we present predictions both on the positron fraction and on the flux for already running or planned space experiments, concluding that they have the potential to discriminate a possible signal from the background and, in some cases, to distinguish among different astrophysical propagation models.

This work presents the calculation of the relation between the bare coupling constant $g_0$ and the $\overline{\mathrm{MS}}$-renormalized coupling $g_{\overline{\mathrm{MS}}}$, $g_0=Z_g(g_0,a\mu )g_{\overline{\mathrm{MS}}}$, to 2 loops in perturbation theory, with fermions in an arbitrary representation of the gauge group $SU(N)$. Our calculation is performed using overlap fermions and Wilson gluons, and the background field technique has been chosen for convenience. The corresponding results in the fundamental representation appear in our longer publication [M. Constantinou and H. Panagopoulos, Phys. Rev. D 76, 114504 (2007)]. The 3-loop coefficient of the bare $\beta$-function, $b_2^L$, is extracted using the 2-loop expression for $Z_g$, and it is presented as a function of the overlap parameter $\rho$, the number of fermion flavors ($N_f$) and the number of colors ($N$). We also provide the expression for the ratio of energy scales ${\Lambda }_L/{\Lambda }_{\overline{\mathrm{MS}}}$, in an arbitrary representation. A plot of ${\Lambda }_L/{\Lambda }_{\overline{\mathrm{MS}}}$ is given in the adjoint representation.

We explore in detail the effective matter fermion mass sum-rules in a class of renormalizable SUSY $SO(10)$ grand unified models where the quark and lepton mass and mixing patterns originate from nondecoupling effects of an extra vector matter multiplet living around the unification scale. If the renormalizable type-II contribution governed by the $SU(2{)}_L$-triplet in ${54}_H$ dominates the seesaw formula, we obtain an interesting correlation between the maximality of the atmospheric neutrino mixing and the proximity of $y_s/y_b$ to $|V_{cb}|$ in the quark sector.