We conjecture that the inflation models with trans-Planckian excursions in the field space should be in the swampland. We check this conjecture in a few examples and investigate the constraints on the spectral index for the slow-roll inflation model in the string landscape where the variation of the inflaton during the period of inflation is less than the Planck scale $M_p$. A red primordial power spectrum with a lower bound on the spectral index is preferred. Both the tensor-scalar ratio and the running can be ignored.

We study analytical properties of the hard exclusive process amplitudes. We found that QCD factorization for deeply virtual Compton scattering and hard exclusive vector meson production results in the subtracted dispersion relation with the subtraction constant determined by the Polyakov-Weiss $D$-term. The relation of this constant to the fixed pole contribution found by Brodsky, Close, and Gunion and defined by parton distributions is studied and proved for momentum transfers exceeding the typical hadronic scale. The continuation to the real photon limit is considered, and the numerical correspondence between lattice simulations of the $D$-term and low energy Thomson amplitude is found. For sufficiently large $t$ the subtraction may be expressed in a form similar to that suggested earlier for real Compton scattering.

We investigate new physics models that can increase the lifetime differences in the $B_q\mathrm{\text{−}}{\overline{B}}_q$ systems ($q=d$, $s$) above their standard model values. If both $B_q$ as well as ${\overline{B}}_q$ can decay to a final state through flavor dependent new physics interactions, the so-called Grossman bound may be evaded. As examples, we consider the scalar leptoquark model and ${\lambda }^{\prime \prime }$-type $R$-parity violating supersymmetry. We find that models with a scalar leptoquark can enhance $\Delta {\Gamma }_s/{\Gamma }_s$ all the way up to its experimental upper bound and $\Delta {\Gamma }_d/{\Gamma }_d$ to as much as $\sim 2.5\%$, at the same time allowing the $CP$ violating phase ${\beta }_s$ to vary between $-45°$ and 20°. $R$-parity violating supersymmetry models cannot enhance the lifetime differences significantly, but can enhance the value of ${\beta }_s$ up to $\sim \pm 20°$. This may bring the values of $\Delta {\Gamma }_q/{\Gamma }_q$ as well as ${\beta }_s$ within the measurement capabilities of $B$ factories and the $B$ physics experiment at the Large Hadron Collider (LHCb). We also obtain bounds on combinations of these new physics couplings, and predict enhanced branching ratios of $B_{s/d}\to {\tau }^{+}{\tau }^{-}$.

The PHENIX experiment presents results from the Relativistic Heavy Ion Collider 2005 run with polarized proton collisions at $\sqrt{s}=200\mathrm{GeV}$, for inclusive ${\pi }^0$ production at midrapidity. Unpolarized cross section results are given for transverse momenta $p_T=0.5$ to $20\mathrm{GeV}/c$, extending the range of published data to both lower and higher $p_T$. The cross section is described well for $p_T<1\mathrm{GeV}/c$ by an exponential in $p_T$, and, for $p_T>2\mathrm{GeV}/c$, by perturbative QCD. Double helicity asymmetries $A_{LL}$ are presented based on a factor of 5 improvement in uncertainties as compared to previously published results, due to both an improved beam polarization of 50%, and to higher integrated luminosity. These measurements are sensitive to the gluon polarization in the proton. Using one representative model of gluon polarization it is demonstrated that the gluon spin contribution to the proton spin is significantly constrained.

We analyze renormalization and the high-temperature expansion of the one-loop effective action of the space-time noncommutative ${\varphi }^4$ theory by using the zeta-function regularization in the imaginary-time formalism (i.e., on $S^1\times {\mathbb{R}}^3$). Interestingly enough, there are no mixed (nonplanar) contributions to the counterterms as well as to the power-law high-temperature asymptotics. We also study the Wick rotation and formulate assumptions under which the real and imaginary-time formalisms are equivalent.

The static Coulomb potential of quantum electrodynamics (QED) is calculated in the presence of a strong magnetic field in the lowest Landau level approximation using two different methods. First, the vacuum expectation value of the corresponding Wilson loop is calculated perturbatively in two different regimes of dynamical mass $m_{\mathrm{dyn}}$, i.e., $|{\mathbf{q}}_{\parallel }^2|\ll m_{\mathrm{dyn}}^2\ll |eB|$ and $m_{\mathrm{dyn}}^2\ll |{\mathbf{q}}_{\parallel }^2|\ll |eB|$, where ${\mathbf{q}}_{\parallel }$ is the longitudinal component of the momentum relative to the external magnetic field $B$. The result is then compared with the static potential arising from Born approximation. Both results coincide. Although the arising potentials show different behavior in the aforementioned regimes, a novel dependence on the angle $\theta$ between the particle-antiparticle’s axis and the direction of the magnetic field is observed. In the regime $|{\mathbf{q}}_{\parallel }^2|\ll m_{\mathrm{dyn}}^2\ll |eB|$, for strong enough magnetic field and depending on the angle $\theta$, a qualitative change occurs in the Coulomb-like potential; whereas for $\theta =0$, $\pi$ the potential is repulsive, it exhibits a minimum for angles $\theta \in ]0,\pi [$.

Plasma instabilities can play a fundamental role in quark-gluon plasma equilibration in the high energy (weak coupling) limit. Early simulations of the evolution of plasma instabilities in non-Abelian gauge theory, performed in one spatial dimension, found behavior qualitatively similar to traditional QED plasmas. Later simulations of the fully three-dimensional theory found different behavior, unlike traditional QED plasmas. To shed light on the origin of this difference, we study the intermediate case of two spatial dimensions. Depending on how the “two-dimensional” theory is formulated, we can obtain either behavior.

The Randall-Sundrum warped braneworld model is generalized to six and higher dimensions such that the warping has a nontrivial dependence on more than one dimension. This naturally leads to a brane-boxlike configuration along with scalar fields with possibly interesting cosmological roles. Also obtained naturally are two towers of 3 branes with mass scales clustered around either of the Planck scale and TeV scale. Such a scenario has interesting phenomenological consequences including an explanation for the observed hierarchy in the masses of standard model fermions.

We study the behavior of quark and diquark condensates in the framework of the extended Nambu–Jona-Lasinio model under the influence of a gravitational field in the static $D$-dimensional Einstein universe at finite temperature and quark density. The thermodynamic potential and the gap equations for the model are obtained. Quark and diquark condensates as functions of the chemical potential and temperature at different values of the curvature have been studied. Phase portraits of the system have been constructed.

We address the problem of constructing high-accuracy, faithful analytic waveforms describing the gravitational wave signal emitted by inspiralling and coalescing binary black holes. We work within the effective-one-body (EOB) framework and propose a methodology for improving the current (waveform) implementations of this framework based on understanding, element by element, the physics behind each feature of the waveform and on systematically comparing various EOB-based waveforms with exact waveforms obtained by numerical relativity approaches. The present paper focuses on small-mass-ratio nonspinning binary systems, which can be conveniently studied by Regge-Wheeler-Zerilli-type methods. Our results include (i) a resummed, 3 PN-accurate description of the inspiral waveform, (ii) a better description of radiation reaction during the plunge, (iii) a refined analytic expression for the plunge waveform, (iv) an improved treatment of the matching between the plunge and ring-down waveforms. This improved implementation of the EOB approach allows us to construct complete analytic waveforms which exhibit a remarkable agreement with the exact ones in modulus, frequency, and phase. In particular, the analytic and numerical waveforms stay in phase, during the whole process, within $\pm 1.1\%$ of a cycle. We expect that the extension of our methodology to the comparable-mass case will be able to generate comparably accurate analytic waveforms of direct use for the ground-based network of interferometric detectors of gravitational waves.

Quantum field theory in a semiclassical background can be derived as an approximation to quantum gravity from a weak-coupling expansion in the inverse Planck mass. Such an expansion is studied for evolution on “nice slices” in the spacetime describing a black hole of mass $M$. Arguments for a breakdown of this expansion are presented, due to significant gravitational coupling between fluctuations, which is consistent with the statement that existing calculations of information loss in black holes are not reliable. For a given fluctuation, the coupling to subsequent fluctuations becomes of order unity by a time of order $M^3$. Lack of a systematic derivation of the weakly coupled/semiclassical approximation would indicate a role for the nonperturbative dynamics of gravity, and possibly for the proposal that such dynamics has an essentially nonlocal quality.

We investigate the quantum particle creation during the circularly symmetric collapse of a $2+1$ dust cloud, for the cases when the cosmological constant is either zero or negative. We derive the Ford-Parker formula for the $2+1$ case, which can be used to compute the radiated quantum flux in the geometric optics approximation. It is shown that no particles are created when the collapse ends in a naked singularity, unlike in the $3+1$ case. When the collapse ends in a Banados-Teitelboim-Zanelli black hole, we recover the expected Hawking radiation.

Brane world models with a nonminimally coupled bulk scalar field have been studied recently. In this paper we consider metric fluctuations around an arbitrary gravity-scalar background solution, and we show that the corresponding spectrum includes a localized zero mode which strongly depends on the profile of the background scalar field. For a special class of solutions, with a warp factor of the RS form, we solve the linearized Einstein equations, for a pointlike mass source on the brane, by using the brane bending formalism. We see that general relativity on the brane is recovered only if we impose restrictions on the parameter space of the models under consideration.

A Kerr black hole with mass parameter $m$ and angular momentum parameter $a$ acting as a gravitational lens gives rise to two images in the weak field limit. We study the corresponding magnification relations, namely, the signed and absolute magnification sums and the centroid up to post-Newtonian order. We show that there are post-Newtonian corrections to the total absolute magnification and centroid proportional to $a/m$, which is in contrast to the spherically symmetric case where such corrections vanish. Hence we also propose a new set of lensing observables for the two images involving these corrections, which should allow measuring $a/m$ with gravitational lensing. In fact, the resolution capabilities needed to observe this for the Galactic black hole should in principle be accessible to current and near-future instrumentation. Since $a/m>1$ indicates a naked singularity, a most interesting application would be a test of the cosmic censorship conjecture. The technique used to derive the image properties is based on the degeneracy of the Kerr lens and a suitably displaced Schwarzschild lens at post-Newtonian order. A simple physical explanation for this degeneracy is also given.

Perturbative gravity about a de Sitter background motivates a global picture of quantum dynamics in “eternal de Sitter space,” the theory of states which are asymptotically de Sitter to both future and past. Eternal de Sitter physics is described by a finite-dimensional Hilbert space in which each state is precisely invariant under the full de Sitter group. This resolves a previously noted tension between de Sitter symmetry and finite entropy. Observables, implications for Boltzmann brains, and Poincaré recurrences are briefly discussed.

The interplay between cosmological expansion and local attraction in a gravitationally bound system is revisited in various regimes. First, weakly gravitating Newtonian systems are considered, followed by various exact solutions describing a relativistic central object embedded in a Friedmann universe. It is shown that the “all or nothing” behavior recently discovered (i.e., weakly coupled systems are comoving while strongly coupled ones resist the cosmic expansion) is limited to the de Sitter background. New exact solutions are presented which describe black holes perfectly comoving with a generic Friedmann universe. The possibility of violating cosmic censorship for a black hole approaching the big rip is also discussed.

We investigate the effects of $1/f$ noise on the ability of a particular class of cosmic microwave background experiments to measure the angular power spectrum of temperature anisotropy. We concentrate on experiments that operate primarily in raster-scan mode and develop formalism that allows us to calculate analytically the effect of $1/f$ noise on power-spectrum sensitivity for this class of experiments and determine the benefits of raster-scanning at different angles relative to the sky field versus scanning at only a single angle (cross-linking versus not cross-linking). We find that the sensitivity of such experiments in the presence of $1/f$ noise is not significantly degraded at moderate spatial scales ($\ell \sim 100$) for reasonable values of scan speed and $1/f$ knee. We further find that the difference between cross-linked and non-cross-linked experiments is small in all cases and that the non-cross-linked experiments are preferred from a raw sensitivity standpoint in the noise-dominated regime—i.e., in experiments in which the instrument noise is greater than the sample variance of the target power spectrum at the scales of interest. This analysis does not take into account systematic effects.

Unparticles as suggested recently by Georgi have surprising phenomenological implications, distinctive from any other new physics that we know of. But they must interact very feebly with ordinary matter to have avoided detection thus far. We determine how feebly they can interact with the electron, using the precisely measured quantities in QED: the electron $g-2$ and the bounds on invisible and exotic positronium decays. The most stringent bound comes from invisible orthopositronium decays: the effective energy scale entering the vector unparticle-electron interaction must exceed $4\times {10}^5\mathrm{TeV}$ for a scaling dimension $\frac{3}{2}$ of the vector unparticle. The lower bounds on scales for other unparticles range from a few tens to a few hundreds TeV. This makes the detection of unparticles challenging in low energy electron systems.

We test the validity of the QCD sum rules applied to the light scalar mesons, the charmed mesons $D_{s0}(2317)$ and $D_{s1}(2460)$, and the $X(3872)$ axial meson, considered as tetraquark states. We find that, with the studied currents, it is possible to find an acceptable Borel window only for the $X(3872)$ meson. In such a Borel window we have simultaneously a good operator product expansion convergence and a pole contribution which is bigger than the continuum contribution. These results may indicate that light many-quark states cannot be considered as resonances separated from the continuum.

We have recently proposed a simple SU(5) theory with an adjoint fermionic multiplet on top of the usual minimal spectrum. This leads to the hybrid scenario of both type I and type III seesaw and it predicts the existence of the fermionic SU(2) triplet between 100 GeV and 1 TeV for a conventional grand unified theory scale of about ${10}^{16}\mathrm{GeV}$, with main decays into $W$ ($Z$) and leptons, correlated through Dirac Yukawa couplings, and lifetimes shorter than about ${10}^{-12}\sec $. These decays are lepton number violating and they offer an exciting signature of $\Delta L=2$ dilepton events together with 4 jets at future $pp$ ($p\overline{p}$) colliders. Increasing the triplet mass endangers the proton stability and so the seesaw mechanism could be directly testable at LHC.