We address the construction and interpretation of diffeomorphism-invariant observables in a low-energy effective theory of quantum gravity. The observables we consider are constructed as integrals over the space of coordinates, in analogy to the construction of gauge-invariant observables in Yang-Mills theory via traces. As such, they are explicitly nonlocal. Nevertheless we describe how, in suitable quantum states and in a suitable limit, the familiar physics of local quantum field theory can be recovered from appropriate such observables, which we term “pseudolocal.” We consider measurement of pseudolocal observables, and describe how such measurements are limited by both quantum effects and gravitational interactions. These limitations support suggestions that theories of quantum gravity associated with finite regions of spacetime contain far fewer degrees of freedom than do local field theories.

Recent observations, particularly from the HESS Collaboration, have revealed rich Galactic populations of TeV gamma-ray sources, including a collection unseen in other wavelengths. Many of these gamma-ray spectra are well measured up to $\sim 10\mathrm{TeV}$, where low statistics make observations by air Čerenkov telescopes difficult. To understand these mysterious sources, especially at much higher energies—where a cutoff should eventually appear—new techniques are needed. We point out the following: (1) For a number of sources, it is very likely that pions, and hence TeV neutrinos, are produced; (2) As a general point, neutrinos should be a better probe of the highest energies than gamma rays, due to increasing detector efficiency; and (3) For several specific sources, the detection prospects for ${\mathrm{km}}^3$ neutrino telescopes are very good, $\sim 1–10$ events/year, with low atmospheric neutrino background rates above reasonable energy thresholds. Such signal rates, as small as they may seem, will allow neutrino telescopes to powerfully discriminate between models for the Galactic TeV sources, with important consequences for our understanding of cosmic-ray production.

Observations of the gravitational radiation from well-localized, inspiraling compact-object binaries can measure absolute source distances with high accuracy. When coupled with an independent determination of redshift through an electromagnetic counterpart, these standard sirens can provide an excellent probe of the expansion history of the Universe and the dark energy. Short $\gamma$-ray bursts, if produced by merging neutron star binaries, would be standard sirens with known redshifts detectable by ground-based gravitational wave (GW) networks such as Advanced Laser Interferometer Gravitational-wave Observatory (LIGO), Virgo, and Australian International Gravitational Observatory (AIGO). Depending upon the collimation of these GRBs, the measurement of about 10 GW-GRB events (corresponding to about 1 yr of observation with an advanced GW detector network and an all-sky GRB monitor) can measure the Hubble constant $h$ to $\sim 2–3\%$. When combined with measurement of the absolute distance to the last scattering surface of the cosmic microwave background, this determines the dark energy equation of state parameter $w$ to $\sim 9\%$. Similarly, supermassive binary black hole inspirals will be standard sirens detectable by Laser Interferometer Space Antenna (LISA). Depending upon the precise redshift distribution, $\sim 100$ sources could measure $w$ at the $\sim 4\%$ level.

We investigate the quark-lepton symmetric gauge group in five dimensions, with the gauge symmetry broken by a combination of orbifold compactification of the extra dimension and the Higgs mechanism. The gauge sector of the model is investigated and contrasted with the four dimensional case. We obtain lower bounds on the mass of the exotic gauge bosons, the inverse compactification scale and the exotic leptons. Light neutrinos are obtained without requiring any scale larger than a TeV. However an ultraviolet cutoff of order ${10}^{11}\mathrm{GeV}$ is required to suppress proton decay inducing nonrenormalizable operators.

We compute the supersymmetry (SUSY) effective Hamiltonian that describes the $|\Delta S|=1$ semileptonic decays of tau leptons. We provide analytical expressions for supersymmetric contribution to $\tau \to u\overline{s}{\nu }_{\tau }$ transition in mass insertion approximation. We show that SUSY contributions may enhance the $CP$ asymmetry of $\tau \to K\pi {\nu }_{\tau }$ decays by several orders of magnitude with respect to the standard model expectations. However, the resulting asymmetry is still well below the current experimental limits obtained by CLEO Collaborations. We emphasize that measuring $CP$ rate asymmetry in this decay larger than ${10}^{-6}$ would be a clear evidence of physics beyond the supersymmetric extensions of the standard model.

The Clebsch-Gordan decomposition is calculated for direct products of the irreducible representations of the cubic space group. These results are used to identify multiparticle states which appear in the hadron spectrum on the lattice. Consideration of the cubic space group indicates how combinations of both zero momentum and nonzero momentum multiparticle states contribute to the spectrum.

Two-pion transitions in charmonium and bottomonium are considered with the leading relativistic effects taken into account. It is estimated that the contribution of the chromo-magnetic interaction of the charmed quarks to the amplitude of the decay $\psi (2S)\to \pi \pi J/\psi$ is at the level of (15–20)%. This contribution is enhanced by a factor of 3 in the decay ${\eta }_c(2S)\to \pi \pi {\eta }_c$, producing a significant modification of the rate and the spectrum in the latter decay. It is also suggested that the peculiar observed spectrum in the decay ${\rm Y}(3S)\to \pi \pi {\rm Y}$ can be explained by a relative prominence of the relativistic terms, if the leading nonrelativistic quarkonium amplitude is dynamically suppressed. Also discussed are the effects of the final state interaction between the pions.

Solar flares accelerate charged particles through a variety of mechanisms, which may be constrained through observations at high energies ($>10\mathrm{GeV}$). We report here a search for direct emission of protons of energy $\gtrsim 20\mathrm{GeV}$ in association with an X17 class solar flare that occurred on 28 October 2003, using a large area tracking muon telescope of the GRAPES-3 experiment at Ooty. Some features of the telescope, including its novel capability of high sensitivity search for the directional enhancement of the solar protons are also described. A 99% C.L. upper limit on the flux of protons due to the solar flare has been placed at $1.4\times {10}^{-6}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{sr}}^{-1}$. A separate upper limit on the narrow solid angle flux of protons at $4\times {10}^{-6}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{sr}}^{-1}$ is also placed. Solar flares are also associated with coronal mass ejections, which propagate through the interplanetary space producing geomagnetic storms and Forbush decrease (Fd) events, upon their arrival at the Earth. New information on the structure and time evolution of the large Fd observed on 29 October 2003 by GRAPES-3 is presented. The onset of Fd in nine different solid angle bins ($\sim 0.3\mathrm{sr}$) shows a remarkably similar behavior, with an evolution on a time scale of $\sim 1\mathrm{h}$. A power law dependence of the magnitude of the Fd on the cutoff rigidity has been derived, using the data from tracking muon telescope, over a narrow range of cutoff rigidity 14.3–24.0 GV, which shows a spectral slope “$\gamma =0.53\pm 0.04$,” in agreement with earlier measurements.

Superposed electrovac $pp$-waves causes chaos. To show this, we project the particle geodesics onto the $(x,y)$ plane and simulate the phase space’s Poincaré section numerically. Similar considerations apply, with minor modifications, to the geodesics in a non-Abelian plane wave spacetime.

We show that in a class of universal extra dimension models (UED), which solves both the neutrino mass and proton decay problem, an admixture of Kaluza-Klein (KK) photon and KK right-handed neutrinos can provide the required amount of cold dark matter (CDM). This model has two parameters $R^{-1}$ and $M_{Z^{\prime }}$ ($R$ is the radius of the extra space dimensions and $Z^{\prime }$ the extra neutral gauge boson of the model). Using the value of the relic CDM density, combined with the results from the cryogenic searches for CDM, we obtain upper limits on $R^{-1}$ of about 400–650 GeV and $M_{Z^{\prime }}\le 1.5\mathrm{TeV}$, both being accessible to the LHC. In some regions of the parameter space, the dark matter-nucleon scattering cross section can be as high as ${10}^{-44}{\mathrm{cm}}^2$, which can be probed by the next round of dark matter search experiments.

We revisit the $4D$ generalized black hole geometries, obtained by us [14], with a renewed interest, to unfold some aspects of effective gravity in a noncommutative $D_3$-brane formalism. In particular, we argue for the existence of extra dimensions in the gravity decoupling limit in the theory. We show that the theory is rather described by an ordinary geometry and is governed by an effective string theory in $5D$. The extremal black hole geometry ${\mathrm{AdS}}_5$ obtained in effective string theory is shown to be in precise agreement with the gravity dual proposed for $D_3$-brane in a constant magnetic field. Kaluza-Klein compactification is performed to obtain the corresponding charged black hole geometries in $4D$. Interestingly, they are shown to be governed by the extremal black hole geometries known in string theory. The attractor mechanism is exploited in effective string theory underlying a noncommutative $D_3$-brane and the macroscopic entropy of a charged black hole is computed. We show that the generalized black hole geometries in a noncommutative $D_3$-brane theory are precisely identical to the extremal black holes known in $4D$ effective string theory.

We study the quasinormal spectrum of a massive scalar field in a $D$-dimensional black hole background. We found a qualitatively different dependence of the fundamental modes on the field mass for $D\ge 6$. The behavior of higher modes is qualitatively the same for all $D$. Thus for some particular values of $\mu M^{1/(D-3)}$, where $\mu$ is the field mass and $M$ is the black hole mass, the spectrum has two dominating oscillations with a very long lifetime. We show that the asymptotically high overtones do not depend on the field mass. In addition, we present the generalization of the Nollert improvement of the continued fraction technique for the numerical calculation of quasinormal frequencies of $D$-dimensional black holes.

In the noncommutative spacetime the fine tuning in KKLMMT model can be significantly released and a nice running of spectral index fitting the WMAP 3 yr data can be achieved. The fitting results show that the noncommutative mass scale is roughly $5\times {10}^{14}\mathrm{Gev}$. The string mass scale is higher than the noncommutative scale unless the string coupling is smaller than ${10}^{-10}$.

We study the effect of free streaming in a universe with cosmic strings with time-varying tension as well as with constant tension. Although current cosmological observations suggest that fluctuation seeded by cosmic strings cannot be the primary source of cosmic density fluctuation, some contributions from them are still allowed. Since cosmic strings actively produce isocurvature fluctuation, the damping of small scale structure via free streaming by dark matter particles with large velocity dispersion at the epoch of radiation-matter equality is less efficient than that in models with conventional adiabatic fluctuation. We discuss its implications to the constraints on the properties of particles such as massive neutrinos and warm dark matter.

Dark matter annihilation has been proposed to explain the TeV gamma rays observed from the Galactic Center. We study constraints on this hypothesis coming from the mass profile around the Galactic Center measured by observing stellar dynamics. We show that for several proposed WIMP candidates, the constraints on the dark matter density profile from measurements of mass by infrared observations are comparable to the constraints from the measurements of the TeV source extension.

We present a five-dimensional model compactified on an interval where supersymmetry is broken by the Scherk-Schwarz mechanism. The gauge sector propagates in the bulk, two Higgs hypermultiplets are quasilocalized, and quark and lepton multiplets localized, in one of the boundaries. The effective four-dimensional theory is the MSSM with very heavy gauginos, heavy squarks, and light sleptons and Higgsinos. The soft tree-level squared masses of the Higgs sector can be negative and they can (partially) cancel the positive one-loop contributions from the gauge sector. Electroweak symmetry breaking can then comfortably be triggered by two-loop radiative corrections from the top-stop sector. The fine-tuning required to obtain the electroweak scale is found to be much smaller than in the MSSM, with essentially no fine-tuning for few TeV gaugino masses. All bounds from direct Higgs searches at LEP and from electroweak precision observables can be satisfied. The lightest supersymmetric particle is a (Higgsino-like) neutralino that can accommodate the abundance of dark matter consistently with recent Wilkinson Microwave Anisotropy Probe (WMAP) observations.

The large top quark mass suggests that the top plays a pivotal role in electroweak symmetry-breaking dynamics and, as a result, may have modified couplings to electroweak bosons. Hadron colliders can provide measurements of these couplings at the $\sim 10\%$ level, and one of the early expected triumphs of the International Linear Collider (ILC) is to reduce these uncertainties to the percent level. In this article, we propose the first direct measurement of the standard model $W\mathrm{\text{−}}t\mathrm{\text{−}}b$ coupling at the ILC, from measurements of $t\overline{t}$-like signals below the $t\overline{t}$ production threshold. We estimate that the ILC with $100{\mathrm{fb}}^{-1}$ can measure a combination of the coupling and top width to high precision, and when combined with a direct measurement of the top width from the above-threshold scan, results in a model-independent measurement of the $W\mathrm{\text{−}}t\mathrm{\text{−}}b$ interaction of the order of $\sim 3\%$.

Muon backgrounds at Super-Kamiokande, KamLAND, and CHOOZ are calculated using $\mathtt{M}\mathtt{U}\mathtt{S}\mathtt{I}\mathtt{C}$. A modified version of the Gaisser sea-level muon distribution and a well-tested Monte Carlo integration method are introduced. Average muon energy, flux, and rate are tabulated. Plots of average energy and angular distributions are given. Implications for muon tracker design in future experiments are discussed.

We calculate the radiative decay amplitude for Majorana neutrinos in trilinear $R$-parity violating supersymmetric framework. Our results make no assumption regarding the masses and mixings of fermions and sfermions. The results obtained are exemplary for generic models with loop-generated neutrino masses. Comparison of this amplitude with the neutrino mass matrix shows that the two provide independent probes of $CP$-violating phases.