We study the evolution of cosmological fluctuations during and after inflation driven by a scalar field coupled to a perfect fluid through a friction term. During the slow-roll regime for the scalar field, the perfect fluid is also frozen and isocurvature perturbations are generated. After the end of inflation, during the decay of the inflaton, we find that a change in the observationally relevant large scale curvature fluctuations is possible.

A search for TeV-PeV muon neutrinos from unresolved sources was performed on AMANDA-II data collected between 2000 and 2003 with an equivalent live time of 807 days. This diffuse analysis sought to find an extraterrestrial neutrino flux from sources with nonthermal components. The signal is expected to have a harder spectrum than the atmospheric muon and neutrino backgrounds. Since no excess of events was seen in the data over the expected background, an upper limit of ${\mathrm{E}}^2{\Phi }_{90\%\mathrm{C}.\mathrm{L}.}<7.4\times {10}^{-8}\mathrm{GeV}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{sr}}^{-1}$ is placed on the diffuse flux of muon neutrinos with a $\Phi \propto {\mathrm{E}}^{-2}$ spectrum in the energy range 16 TeV to 2.5 PeV. This is currently the most sensitive $\Phi \propto {\mathrm{E}}^{-2}$ diffuse astrophysical neutrino limit. We also set upper limits for astrophysical and prompt neutrino models, all of which have spectra different from $\Phi \propto {\mathrm{E}}^{-2}$.

In view of the newly discovered and physically acceptable $PT$ symmetric and non-Hermitian models, we reinvestigated the phase structure of the $(g{\varphi }^4+h{\varphi }^6{)}_{1+1}$ Hermitian model. The reinvestigation concerns the possibility of a phase transition from the original Hermitian and $PT$ symmetric phase to a non-Hermitian and $PT$ symmetric one. This kind of phase transition, if verified experimentally, will lead to the first proof that non-Hermitian and $PT$ symmetric models are not just a mathematical research framework but are a nature desire. To do the investigation, we calculated the effective potential up to second order in the couplings and found a Hermitian to non-Hermitian phase transition. This leads us to introduce, for the first time, Hermiticity as a symmetry which can be broken due to quantum corrections, i.e., when starting with a model which is Hermitian in the classical level, quantum corrections can break Hermiticity while the theory stays physically acceptable. In fact, ignoring this phase will lead to violation of universality when comparing these model predictions with other models in the same class of universality. For instance, in a previous work we obtained a second order phase transition for the $PT$ symmetric and non-Hermitian ($-g{\varphi }^4$) model and according to universality, this phase should exist in the phase structure of the ($g{\varphi }^4+h{\varphi }^6$) model for negative $g$. Finally, among the novelties in this paper, in our calculation for the effective potential, we introduced a new renormalization group equation which describes the invariance of the bare vacuum energy under the change of the scale. We showed that without this invariance, the original theory and the effective one are inequivalent.

Relic thermal axions could play the role of an extra hot dark matter component in cosmological structure formation theories. By combining the most recent observational data we improve previous cosmological bounds on the axion mass $m_a$ in the so-called hadronic axion window. We obtain a limit on the axion mass $m_a<0.42\mathrm{eV}$ at the 95% C.L. ($m_a<0.72\mathrm{eV}$ at the 99% C.L.). A novel aspect of the analysis presented here is the inclusion of massive neutrinos and how they may affect the bound on the axion mass. If neutrino masses belong to an inverted hierarchy scheme, for example, the above constraint is improved to $m_a<0.38\mathrm{eV}$ at the 95% C.L. ($m_a<0.67\mathrm{eV}$ at the 99% C.L.). Future data from experiments as CAST will provide a direct test of the cosmological bound.

Unparticles proposed by Georgi carry $CP$ conserving phases in their propagators. We demonstrate that these peculiar phases have an important impact on $CP$ violation. Without including the strong QCD phases, we study the unparticle phase effects on the direct $CP$ asymmetries in the exclusive decays of ${\overline{B}}_d\to {\pi }^{+}{\pi }^{-}$ and $B\to \pi K$, in which the flavor changing neutral currents are forbidden at tree level but induced by one-loop diagrams. Interesting and consistent results comparing to the data are obtained. In addition, we find that unparticles will significantly enhance the differential branching ratio of $b\to s{\ell }^{+}{\ell }^{-}$ at the small invariant mass of ${\ell }^{+}{\ell }^{-}$. The forward-backward asymmetries for $b\to s{\ell }^{+}{\ell }^{-}$ due to unparticles are also explored.

We study the production and decay of Kaluza-Klein (KK) gravitons at the CERN Large Hadron Collider (LHC), in the framework of a warped extra dimension in which the standard model (SM) fields propagate. Such a scenario can provide solutions to both the Planck-weak hierarchy problem and the flavor puzzle of the SM. In this scenario, the production via $q\overline{q}$ annihilation and decays to the conventional photon and lepton channels are highly suppressed. However, we show that graviton production via gluon fusion followed by decay to longitudinal $Z/W$ can be significant; vector boson fusion is found to be a subdominant production mode. In particular, the golden $ZZ$ decay mode offers a distinctive 4-lepton signal that could lead to the observation at the LHC with $300{\mathrm{fb}}^{-1}$ (SLHC with $3{\mathrm{ab}}^{-1}$) of a KK graviton with a mass up to $\sim 2$ ($\sim 3$) TeV for the ratio of the ${\mathrm{AdS}}_5$ curvature to the Planck scale modestly above unity. We argue that (contrary to the lore) such a size of the curvature scale can still be within the regime of validity of the framework. Upgrades beyond the SLHC luminosity are required to discover gravitons heavier than $\sim 4\mathrm{TeV}$, as favored by the electroweak and flavor precision tests in the simplest such models.

We present formulae for the joint angular distributions for $J/\psi$ or $\psi (2S)$ decays into $\Lambda \overline{\Lambda }$, ${\Sigma }^0{\overline{\Sigma }}^0$, ${\Xi }^{-}{\overline{\Xi }}^{+}$, and ${\Omega }^{-}{\overline{\Omega }}^{+}$, which allows the determination of the antihyperon decay parameters using helicity amplitude information. The prospects of measuring the antihyperon decay parameters in these decays are discussed. The estimation of the measurement sensitivity shows that $J/\psi$ decays into $\Lambda \overline{\Lambda }$ and ${\Xi }^{-}{\overline{\Xi }}^{+}$ can be hopefully used to measure the $\overline{\Lambda }$ and ${\overline{\Xi }}^{+}$ decay parameters.

We discuss properties of hypothetical scale invariant (unparticle) matter by viewing it as a tower of massive particles. We show how peculiar properties of unparticles emerge in the limit when the mass spacing parameter $\Delta$ vanishes. We explain why the unparticle cannot decay in this limit and how, for finite $\Delta$, the decays manifest themselves in a relation between the reconstructed invariant mass and vertex displacement. We describe a model field theory in ${\mathrm{AdS}}_5$ which explicitly implements the deconstruction procedure by truncating the extra dimension to size of order $1/\Delta$.

We consider the diffractive production of $J/\psi$ mesons at HERA conditions in the framework of the two-gluon exchange model. We show that the contribution from the real part of the amplitude is of the same order of magnitude as that of the imaginary part and inspect its possible effect on the different kinematic distributions.

We point out that new physics can play an important role in rescuing some of the Yukawa texture-zero Ansätze which would otherwise be eliminated by the recent, more precise measurements of $V_{\mathrm{CKM}}$. As an example, a detailed analysis of a four texture-zero Ansatz is presented, showing how the presence of an isosinglet vectorlike quark, which mixes with standard quarks, can render viable this Yukawa texture. The crucial point is the nondecoupling of the effects of the isosinglet quark, even for arbitrary large values of its mass.

We study Casimir forces on the partition in a closed box (piston) with perfect metallic boundary conditions. Related closed geometries have generated interest as candidates for a repulsive force. By using an optical path expansion we solve exactly the case of a piston with a rectangular cross section, and find that the force always attracts the partition to the nearest base. For arbitrary cross sections, we can use an expansion for the density of states to compute the force in the limit of small height to width ratios. The corrections to the force between parallel plates are found to have interesting dependence on the shape of the cross section. Finally, for temperatures in the range of experimental interest we compute finite temperature corrections to the force (again assuming perfect boundaries).

We study the question of the gauge dependence of the quantum gravity contribution to the running gauge coupling constant for electromagnetism. The calculations are performed using dimensional regularization in a manifestly gauge-invariant and gauge-condition-independent formulation of the effective action. It is shown that there is no quantum gravity contribution to the running charge, and hence there is no alteration to asymptotic freedom at high energies as predicted by Robinson and Wilczek.

We propose a new mechanism of TeV scale leptogenesis where the chemical potential of right-handed electrons is passed on to the $B-L$ asymmetry of the Universe in the presence of sphalerons. The model has the virtue that the origin of neutrino masses is independent of the scale of leptogenesis. As a result, the model could be extended to explain dark matter, dark energy, neutrino masses, and leptogenesis at the TeV scale. The most attractive feature of this model is that it predicts a few hundred GeV triplet Higgs scalar that can be tested at LHC or the International Linear Collider.

Motivated by the severity of the bounds on Lorentz violation in the presence of ordinary gravity, we study frameworks in which Lorentz violation does not affect the spacetime geometry. We show that there are at least two inequivalent classes of spontaneous Lorentz breaking that even in the presence of gravity result in Minkowski space. The first one generically corresponds to the condensation of tensor fields with tachyonic mass, which in turn is related to ghost condensation. In the second class, realized by the Dvali-Gabadadze-Porrati model or theories of massive gravitons, spontaneous Lorentz breaking is induced by the expectation value of sources. The generalization to de Sitter space is also discussed.

We consider the cosmology where some function $f(G)$ of the Gauss-Bonnet term $G$ is added to the gravitational action to account for the late-time accelerating expansion of the universe. The covariant and gauge invariant perturbation equations are derived with a method which could also be applied to general $f(R,R^{ab}{R}_{ab},R^{abcd}{R}_{abcd})$ gravitational theories. It is pointed out that, despite their fourth-order character, such $f(G)$ gravity models generally cannot reproduce arbitrary background cosmic evolutions; for example, the standard $\Lambda \mathrm{CDM}$ paradigm with ${\Omega }_{\mathrm{DE}}=0.76$ cannot be realized in $f(G)$ gravity theories unless $f$ is a true cosmological constant because it imposes exclusionary constraints on the form of $f(G)$. We analyze the perturbation equations and find that, as in the $f(R)$ model, the stability of early-time perturbation growth puts some constraints on the functional form of $f(G)$, in this case ${\partial }^{2}f/\partial G^2<0$. Furthermore, the stability of small-scale perturbations also requires that $f$ not deviate significantly from a constant. These analyses are illustrated by numerically propagating the perturbation equations with a specific model reproducing a representative $\Lambda \mathrm{CDM}$ cosmic history. Our results show how the $f(G)$ models are highly constrained by cosmological data.

We explore observational constraints on possible deviations from Newtonian gravity by means of large-scale clustering of galaxies. We measure the power spectrum and the bispectrum of Sloan Digital Sky Survey galaxies and compare the result with predictions in an empirical model of modified gravity. Our model assumes an additional Yukawa-like term with two parameters that characterize the amplitude and the length scale of the modified gravity. The model predictions are calculated using two methods; second-order perturbation theory and direct $N$-body simulations. These methods allow us to study nonlinear evolution of large-scale structure. Using the simulation results, we find that perturbation theory provides reliable estimates for the power spectrum and the bispectrum in the modified Newtonian model. We also construct mock galaxy catalogs from the simulations, and derive constraints on the amplitude and the length scale of deviations from Newtonian gravity. The resulting constraints from the power spectrum are consistent with those obtained in our earlier, indicating the validity of the previous empirical modeling of gravitational nonlinearity in the modified Newtonian model. If linear biasing is adopted, the bispectrum of the Sloan Digital Sky Survey galaxies yields constraints very similar to those from the power spectrum. If we allow for the nonlinear biasing instead, we find that the ratio of the quadratic to linear biasing coefficients, $b_2/b_1$, should satisfy $-0.25<b_2/b_1<0.19$ for $\lambda =5h^{-1}\mathrm{Mpc}$ and $-0.19<b_2/b_1<0.13$ for $\lambda =10h^{-1}\mathrm{Mpc}$ in the modified Newtonian model.

The symmetry structures of two-dimensional heterotic string theory are studied further. A $(2d+n)\times (2d+n)$ matrix complex $H$-potential is constructed and the field equations are extended into a complex matrix formulation. A pair of Hauser-Ernst-type linear systems are established. Based on these linear systems, explicit formulations of new hidden symmetry transformations for the considered theory are given and then these symmetry transformations are verified to constitute infinite-dimensional Lie algebras: the semidirect product of the Kac-Moody $o(\widehat{d,d+n})$ and Virasoro algebras (without center charges). These results demonstrate that the heterotic string theory under consideration possesses more and richer symmetry structures than previously expected.

The Tolman-Oppenheimer-Volkov (TOV) equation constrains the internal structure of general relativistic static perfect fluid spheres. We develop several “solution generating” theorems for the TOV equation, whereby any given solution can be deformed into a new solution. Because the theorems we develop work directly in terms of the physical observables—pressure profile and density profile—it is relatively easy to check the density and pressure profiles for physical reasonableness. This work complements our previous article [Phys. Rev. D 71, 124037 (2005)] wherein a similar algorithmic analysis of the general relativistic static perfect fluid sphere was presented in terms of the spacetime geometry—in the present analysis the pressure and density are primary and the spacetime geometry is secondary. In particular, our deformed solutions to the TOV equation are conveniently parametrized in terms of $\delta {\rho }_c$ and $\delta p_c$, the finite shift in the central density and central pressure. We conclude by presenting a new physical and mathematical interpretation for the TOV equation—as an integrability condition on the density and pressure profiles.

Using a Liouville measure, similar to the one proposed recently by Gibbons and Turok, we investigate the probability that single-field inflation with a polynomial potential can last long enough to solve the shortcomings of the standard hot big bang model, within the semiclassical regime of loop quantum cosmology. We conclude that, for such a class of inflationary models and for natural values of the loop quantum cosmology parameters, a successful inflationary scenario is highly improbable.

Relic abundance of dark matter is investigated in the framework of universal extra dimension models with right-handed neutrinos. These models are free from the serious Kaluza-Klein (KK) graviton problem that the original universal extra dimension model has. The first KK particle of the right-handed neutrino is a candidate for dark matter in this framework, and its relic abundance is determined by three processes, (1) the decay of the KK photon into the first KK right-handed neutrino in the late universe, (2) production of the first KK right-handed neutrino from the thermal bath in the early universe, and (3) the decay of higher KK right-handed neutrinos into the first KK right-handed neutrino in the late universe. When ordinary neutrino masses are large enough such as the degenerate mass spectrum case, the last process contributes to the abundance significantly, even if the reheating temperature is low. The scale of the extra dimension consistent with cosmological observations can be 500 GeV in the minimal setup of universal extra dimension models with right-handed neutrinos.