In String Theory compactification, branes are often invoked to get the desired form of the radion effective potential. Current popular way of doing this assumes that the introduction of branes will not modify the background geometry in an important way. In this paper, we show by an explicit example that at least in the codimension two case, the gravitational backreaction of the brane cannot be neglected in deriving the radion effective potential. Actually, in this case, the presence of branes will have no effect on the dynamics of radion.

We propose signals in the cosmic microwave background (CMB) to probe the type and spectrum of neutrino masses. In theories that have spontaneous breaking of approximate lepton flavor symmetries at or below the weak scale, light pseudo-Goldstone bosons recouple to the cosmic neutrinos after nucleosynthesis and affect the acoustic oscillations of the electron-photon fluid during the eV era. Deviations from the Standard Model are predicted for both the total energy density in radiation during this epoch, $\Delta N_{\nu }$, and for the multipole of the $n$’th CMB peak at large $n$, $\Delta l_n$. The latter signal is difficult to reproduce other than by scattering of the known neutrinos, and is therefore an ideal test of our class of theories. In many models, the large shift $\Delta l_n\approx 8n_S$ depends on the number of neutrino species that scatter via the pseudo-Goldstone boson interaction. This interaction is proportional to the neutrino masses, so that the signal reflects the neutrino spectrum. The prediction for $\Delta N_{\nu }$ is highly model dependent, but can be accurately computed within any given model. It is very sensitive to the number of pseudo-Goldstone bosons, and therefore to the underlying symmetries of the leptons, and is typically in the region of $0.03<\Delta N_{\nu }<1$. This signal is significantly larger for Majorana neutrinos than for Dirac neutrinos, and, like the scattering signal, varies as the spectrum of neutrinos is changed from hierarchical to inverse hierarchical to degenerate.

We have studied noncommutative extension of the relativistic Chern-Simons-Higgs model, in the first nontrivial order in $\theta$, with only spatial noncommutativity. Both Lagrangian and Hamiltonian formulations of the problem have been discussed, with the focus being on the canonical and symmetric forms of the energy-momentum tensor. In the Hamiltonian scheme, constraint analysis and the induced Dirac brackets have been provided. The space-time translation generators and their actions on the fields are discussed in detail. The effects of noncommutativity on the soliton solutions have been analyzed thoroughly and we have come up with some interesting observations. Considering the relative strength of the noncommutative effects, we have shown that there is a universal character in the noncommutative correction to the magnetic field—it depends only on $\theta$. On the other hand, in the cases of all other observables of physical interest, such as the potential profile, soliton mass, or the electric field, $\theta$ as well as $\tau$ (the latter comprised solely of commutative Chern-Simons-Higgs model parameters) appear on similar footings. Lastly, we have shown that noncommutativity imposes a further restriction on the form of the Higgs field so that the Bogomolny-Prasad-Sommerfeld equations are compatible with the full variational equations of motion.

Free scalar field theory on a flat spacetime can be cast into a generally covariant form known as parametrized field theory in which the action is a functional of the scalar field as well as the embedding variables which describe arbitrary, in general curved, foliations of the flat spacetime. We construct the path integral quantization of parametrized field theory in order to analyze issues at the interface of quantum field theory and general covariance in a path integral context. We show that the measure in the Lorentzian path integral is nontrivial and is the analog of the Fradkin-Vilkovisky measure for quantum gravity. We construct Euclidean functional integrals in the generally covariant setting of parametrized field theory using key ideas of Schleich and show that our constructions imply the existence of nonstandard “Wick rotations” of the standard free scalar field two-point function. We develop a framework to study the problem of time through computations of scalar field two-point functions. We illustrate our ideas through explicit computation for a time independent $(1+1)$-dimensional foliation. Although the problem of time seems to be absent in this simple example, the general case is still open. We discuss our results in the contexts of the path integral formulation of quantum gravity and the canonical quantization of parametrized field theory.

We examine universal statistical patterns in the chaotic dynamics of three-degree-of-freedom Hamiltonians where long-range interactions are present. These statistical patterns are associated with the presence of a saddle-center-center critical point in the phase space of the systems, being basically discussed in the realm of closed inflationary cosmologies with two scalar fields. In the neighborhood of the critical point, the Hamiltonian is separable into two rotational motion sectors and one hyperbolic motion sector, with respective energies partially conserved. Because of the nonintegrability of the system, the distribution of these quantities for typical ensembles of orbits is chaotic, the associated distribution laws being in the realm of Tsallis nonextensive $q$ thermostatistics. The nonintegrability parameters of the system, the masses $m_1$ and $m_2$ of the scalar fields, and the coupling parameter $g^2$ between the two scalar fields characterize the several routes of the system towards the high nonintegrability limit where the universal statistical patterns show up. A general feature is that the statistical partition of energy between the rotational sectors is made only via the gravitational sector, which plays the role of a reservoir of energy in the partition process. The dominance of the gravitational interaction (as ruled by the mass parameters) in the nonextensivity of the statistics over the interaction ruled by $g^2$ is established. As a striking example, we exhibit a route from Boltzmann-Gibbs behavior towards the nonextensive behavior as the gravitational interaction becomes dominant over the $g^2$ interaction.

Superradiance in black hole spacetimes can trigger instabilities. Here we show that, due to superradiance, small Kerr–anti-de Sitter black holes are unstable. Our demonstration uses a matching procedure, in a long wavelength approximation.

We discuss the possibility that galactic gravitational wave sources might give burst signals at a rate of several events per year, detectable by state-of-the-art detectors. We are stimulated by the results of the data collected by the EXPLORER and NAUTILUS bar detectors in the 2001 run, which suggest an excess of coincidences between the two detectors, when the resonant bars are orthogonal to the galactic plane. Signals due to the coalescence of galactic compact binaries fulfill the energy requirements but are problematic for lack of known candidates with the necessary merging rate. We examine the limits imposed by galactic dynamics on the mass loss of the Galaxy due to gravitational wave (GW) emission, and we use them to put constraints also on the GW radiation from exotic objects, like binaries made of primordial black holes. We discuss the possibility that the events are due to GW bursts coming repeatedly from a single or a few compact sources. We examine different possible realizations of this idea, such as accreting neutron stars, strange quark stars, and the highly magnetized neutron stars (“magnetars”) introduced to explain soft gamma repeaters. Various possibilities are excluded or appear very unlikely, while others at present cannot be excluded.

We reexamine the model of natural inflation, in which the inflaton potential is flat due to shift symmetries. The original version of the model, where the inflaton is a pseudo–Nambu-Goldstone boson with potential of the form $V(\varphi )={\Lambda }^4[1\pm \cos (\varphi /f)]$, is studied in light of recent data. We find that the model is alive and well. Successful inflation as well as data from the Wilkinson Microwave Anisotropy Probe require $f>0.6m_{\mathrm{P}\mathrm{l}}$ (where $m_{\mathrm{P}\mathrm{l}}=1.22\times {10}^{19}\mathrm{G}\mathrm{e}\mathrm{V}$) and $\Lambda \sim m_{\mathrm{G}\mathrm{U}\mathrm{T}}$ (where $m_{\mathrm{G}\mathrm{U}\mathrm{T}}\sim {10}^{16}\mathrm{G}\mathrm{e}\mathrm{V}$), scales which can be accommodated in particle physics models. The detectability of tensor modes from natural inflation in upcoming microwave background experiments is discussed. We find that natural inflation predicts a $\mathrm{\text{tensor}}/\mathrm{\text{scalar}}$ ratio within reach of future observations.

The synthesis of ${}^6\mathrm{L}\mathrm{i}$ during the epoch of big bang nucleosynthesis due to residual annihilation of dark matter particles is considered. By comparing the predicted ${}^6\mathrm{L}\mathrm{i}$ to observations of this isotope in low-metallicity stars, generic constraints on s-wave dark matter annihilation rates into quarks, gauge bosons, and Higgs bosons are derived. It may be shown that, for example, wino dark matter in anomaly-mediated SUSY breaking scenarios with masses $m_{\chi }\lesssim 250\mathrm{G}\mathrm{e}\mathrm{V}$ or light neutralinos with $m_{\chi }\lesssim 20\mathrm{G}\mathrm{e}\mathrm{V}$ annihilating into light quarks are, taking face value, ruled out. These constraints may only be circumvented if significant ${}^6\mathrm{L}\mathrm{i}$ depletion has occurred in all three low-metallicity stars in which this isotope has been observed to date. In general, scenarios invoking nonthermally generated neutralinos with enhanced annihilation rates for a putative explanation of cosmic ray positron or galactic center as well as diffuse background gamma-ray signals by present-day neutralino annihilation will have to face a stringent ${}^6\mathrm{L}\mathrm{i}$ overproduction problem. On the other hand, it is possible that ${}^6\mathrm{L}\mathrm{i}$ as observed in low-metallicity stars is entirely due to residual dark matter annihilation during big bang nucleosynthesis, even for neutralinos undergoing a standard thermal freeze-out.

Inflation universally produces classical almost scale free Gaussian inhomogeneities of any light scalars. Assuming the coupling constants at the time of inflation depend on some light moduli fields, we encounter the generation of modulated cosmological fluctuations from (p)reheating. This is an alternative mechanism to generate observable (almost) scale free adiabatic metric perturbations. We extend this idea to the class of hybrid inflation, where the bifurcation value of the inflaton is modulated by the spatial inhomogeneities of the couplings. As a result, the symmetry breaking after inflation occurs not simultaneously in space but with the time laps in different Hubble patches inherited from the long-wavelength moduli inhomogeneities. To calculate modulated fluctuations we introduce techniques of general relativistic matching conditions for metric perturbations at the time hypersurface where the equation of state after inflation undergoes a jump, without evoking the detailed microscopic physics, as far as it justifies the jump. We apply this theory to the modulated fluctuations from the hybrid and chaotic inflations. We discuss what distinguishes the modulated from the inflation-driven fluctuations, in particular, their spectral index, modification of the consistency relation, and the issue of weak non-Gaussianity.

We analyzed the potential of the LC with $\sqrt{s}=0.5\mathrm{T}\mathrm{e}\mathrm{V}$, $\mathrm{L}\mathrm{C}\otimes \mathrm{L}\mathrm{H}\mathrm{C}$ based $ep$ collider with $\sqrt{s}=3.74\mathrm{T}\mathrm{e}\mathrm{V}$ and the LHC with $\sqrt{s}=14\mathrm{T}\mathrm{e}\mathrm{V}$ to search for excited electrons through transition magnetic type couplings with gauge bosons. The $e^{\star }\to e\gamma$ signal and corresponding backgrounds are studied in detail.

We present the general formalism for studying $CP$-violating phenomena in the production, mixing and decay of a coupled system of $CP$-violating neutral Higgs bosons at high-energy colliders. Considering the minimal supersymmetric standard model (MSSM) Higgs sector in which $CP$ violation is radiatively induced by phases in the soft supersymmetry-breaking third-generation trilinear squark couplings and gaugino masses, we apply our formalism to neutral Higgs production via $\overline{b}b$, $gg$ and $W^{+}{W}^{-}$ collisions at the CERN LHC. We discuss $CP$ asymmetries in the longitudinal and transverse polarizations of ${\tau }^{+}{\tau }^{-}$ pairs. The signatures of $CP$ violation are more prominent in the production via $gg$ and $W^{+}{W}^{-}$ than via $\overline{b}b$, and are resonantly enhanced when two (or all three) neutral Higgs bosons are nearly degenerate with mass differences comparable to their decay widths. Such scenarios occur naturally in the MSSM for values of $\tan \beta \gtrsim 5(30)$ and large (small) charged Higgs-boson masses. We analyze representative examples with large mixing between the three neutral Higgs bosons weighing about 120 GeV, that may exhibit observable $CP$ asymmetries even as large as 80%.

We present an ultraviolet extension of the “simplest little Higgs” model. The model marries the simplest little Higgs at low energies to two copies of the “littlest Higgs” at higher energies. The result is a weakly coupled theory below 100 TeV with a naturally light Higgs. The higher cutoff suppresses the contributions of strongly coupled dynamics to dangerous operators such as those which induce flavor changing neutral currents and CP violation. We briefly survey the distinctive phenomenology of the model.

Recently, Higgsless models of electroweak symmetry breaking have been proposed. Based on compactified five-dimensional gauge theories, these models achieve unitarity of electroweak boson self-interactions through the exchange of a tower of massive vector bosons rather than the exchange of a scalar Higgs boson. In this paper, using deconstruction, we analyze the form of the corrections to the electroweak interactions in a large class of these models, allowing for arbitrary 5-D geometry, position-dependent gauge coupling, and brane kinetic-energy terms. We show that many models considered in the literature, including those most likely to be phenomenologically viable, are in this class. By analyzing the asymptotic behavior of the correlation function of gauge currents at high momentum, we extract the exact form of the relevant correlation functions at tree level and compute the corrections to precision electroweak observables in terms of the spectrum of heavy vector bosons. We determine when nonoblique corrections due to the interactions of fermions with the heavy vector bosons become important, and specify the form such interactions can take. In particular, we find that in this class of models, so long as the theory remains unitary, $S-4{cos}^2{\theta }_{W}T>\mathcal{O}(1)$, where $S$ and $T$ are the usual oblique parameters. We concur with the result of Cacciapaglia et al. that small or negative $S$ is possible—though only at the expense of substantial negative $T$ at tree level. Although we stress our results as they apply to continuum 5-D models, they apply also to models of extended electroweak gauge symmetries motivated by models of hidden local symmetry.

We study the excited-state potential and the gluonic excitation in the static three-quark (3Q) system using $\mathrm{S}\mathrm{U}(3)$ lattice QCD with ${16}^3\times 32$ at $\beta =5.8$ and 6.0 at the quenched level. For about 100 different patterns of spatially-fixed 3Q systems, we accurately extract the excited-state potential $V_{3\mathrm{Q}}^{\mathrm{e}.\mathrm{s}.}$ together with the ground-state potential $V_{3\mathrm{Q}}^{\mathrm{g}.\mathrm{s}.}$ by diagonalizing the QCD Hamiltonian in the presence of three quarks. The gluonic excitation energy $\Delta E_{3\mathrm{Q}}\equiv V_{3\mathrm{Q}}^{\mathrm{e}.\mathrm{s}.}-V_{3\mathrm{Q}}^{\mathrm{g}.\mathrm{s}.}$ is found to be about 1 GeV at the typical hadronic scale. This large gluonic excitation energy is conjectured to give a physical reason of the success of the quark model for low-lying hadrons even without explicit gluonic modes. We investigate the functional form of $\Delta E_{3\mathrm{Q}}$ in terms of the 3Q location. The lattice data of $\Delta E_{3\mathrm{Q}}$ are relatively well reproduced by the “inverse Mercedes Ansatz” with the “modified Y-type flux-tube length,” which indicates that the gluonic excitation mode is realized as a complicated bulk excitation of the whole 3Q system.

We analyze the free energy of a static quark-antiquark pair in quenched QCD at short and large distances. From this we deduce running couplings, $g^2$ ($r$, $T$), and determine the length scale that separates at high temperature the short distance perturbative regime from the large distance nonperturbative regime in the QCD plasma phase. Ambiguities in the definition of a coupling beyond the perturbative regime are discussed in their relation to phenomenological considerations on heavy quark bound states in the quark gluon plasma. Our analysis suggests that it is more appropriate to characterize the nonperturbative properties of the QCD plasma phase close to $T_c$ in terms remnants of the confinement part of the QCD force rather than a strong Coulombic force.

As a result of the identification of the solution to the solar neutrino problem, a rather precise relation ${\theta }_{\mathrm{s}\mathrm{u}\mathrm{n}}+{\theta }_C=\pi /4$ between the leptonic 1-2 mixing angle ${\theta }_{\mathrm{s}\mathrm{u}\mathrm{n}}$ and the Cabibbo angle has emerged. It would mean that the lepton and the quark mixing angles add up to the maximal, suggesting a deep structure by which quarks and leptons are interrelated. We refer to the relation as “quark-lepton complementarity” (QLC) in this paper. We formulate general conditions under which the QLC relation is realized. We then present several scenarios which lead to the relation and elaborate on phenomenological consequences which can be tested by the future experiments. We also discuss implications of the QLC relation for the quark-lepton symmetry and the mechanism of neutrino mass generation.

We discuss the possibility of flavor symmetries to explain the pattern of charged lepton and neutrino masses and mixing angles. We emphasize what are the obstacles for the generation of an almost maximal atmospheric mixing and what are the minimal ingredients to obtain it. A model based on the discrete symmetry $S_3$ is constructed, which leads to the dominant $\mu \tau$-block in the neutrino mass matrix, thus predicting normal hierarchy. This symmetry makes it possible to reproduce current data and predicts $0.01\lesssim {\theta }_{13}\lesssim 0.03$ and strongly suppressed neutrinoless $2\beta$-decay. Moreover, it implies a relation between lepton and quark mixing angles: ${\theta }_{23}^q\approx 2(\pi /4-{\theta }_{23})$. The Cabibbo mixing can also be reproduced and ${\theta }_{13}^q\sim {\theta }_{12}^q{\theta }_{23}^q$. $S_3$ is thus a candidate to describe all the basic features of standard model fermion masses and mixing.

We investigate adding two sterile neutrinos to resolve the apparent tension existing between short-baseline neutrino oscillation results and CPT-conserving, four-neutrino oscillation models. For both $(3+1)$ and $(3+2)$ models, the level of statistical compatibility between the combined dataset from the null short-baseline experiments Bugey, CHOOZ, CCFR84, CDHS, KARMEN, and NOMAD, on the one hand; and the LSND dataset, on the other, is computed. A combined analysis of all seven short-baseline experiments, including LSND, is also performed, to obtain the favored regions in neutrino mass and mixing parameter space for both models. Finally, four statistical tests to compare the $(3+1)$ and the $(3+2)$ hypotheses are discussed. All tests show that $(3+2)$ models fit the existing short-baseline data significantly better than $(3+1)$ models.

We study the lepton flavor-violating (LFV) processes $\mu \to e\gamma$, $\mu \to 3e$, and $\mu \to e$ conversion in nuclei in the left-right symmetric model without supersymmetry and perform the first complete computation of the LFV branching ratios $B(\mu \to f)$ to leading nontrivial order in the ratio of left- and right-handed symmetry-breaking scales. To this order, $B(\mu \to e\gamma )$ and $B(\mu \to e)$ are governed by the same combination of LFV violating couplings, and their ratio is naturally of order unity. We also find $B(\mu \to 3e)/B(\mu \to e)\sim 100$ under slightly stronger assumptions. Existing limits on the branching ratios already substantially constrain mass splittings and/or mixings in the heavy neutrino sector. When combined with future collider studies and precision electroweak measurements, improved limits on LFV processes will test the viability of low-scale, nonsupersymmetric LFV scenarios.