We test gauge/string duality by evaluating expectation values of small Wilson loops in pure Yang-Mills theories. On the gauge theory side, there exists a rich phenomenology. The dual formulation provides a universal language to evaluate the gluon condensate and quadratic correction in terms of the metric in the fifth coordinate. Quantitatively, the estimated value of the gluon condensate is approximately $0.010{\mathrm{GeV}}^4$.

The spontaneous excitation of a two-level atom held static outside a four dimensional Schwarzschild black hole and in interaction with a massless scalar field in the Boulware, Unruh, and Hartle-Hawking vacuums is investigated, and the contributions of the vacuum fluctuations and radiation reaction to the rate of change of the mean atomic energy are calculated separately. We find that, for the Boulware vacuum, the spontaneous excitation does not occur and the ground-state atoms are stable, while the spontaneous emission rate for excited atoms in the Boulware vacuum, which is well behaved at the event horizon, is not the same as that in the usual Minkowski vacuum. However, for both the Unruh vacuum and the Hartle-Hawking vacuum, our results show that the atom would spontaneously excite, as if there were an outgoing thermal flux of radiation or as if it were in a thermal bath of radiation at a proper temperature which reduces to the Hawking temperature in the spatial asymptotic region, depending on whether the scalar field is in the Unruh or Hartle-Hawking vacuum.

Models in extra dimensions have unique features. Many of their surprising properties simply result from the underlying 5D structure. This structure shows up as “sum rules” involving the whole tower of Kaluza-Klein factors. In this paper, we present a holographic shortcut and derive these results without solving the eigenvalue problem: we express 4D physical quantities directly in terms of the 5D metric. In warped space, one can go further and isolate the effect of the new physics sector. This method can be used for any 5D model, and we apply it here to the case of holographic QCD and holographic technicolor.

Gravitational lensing observations of galaxy clusters have identified dark matter blobs with remarkably low baryonic content. We use such a blob to probe the particle nature of dark matter with x-ray observations. From these observations we improve the most conservative constraints from the Milky Way halo on a particular dark matter candidate, the sterile neutrino, by an order of magnitude. We also study high resolution x-ray grating spectra of a cluster of galaxies. Based on these conservative constraints obtained from cosmic x-ray observations alone, the low mass ($m_s\lesssim 10\mathrm{keV}$) and low mixing angle (${sin}^2(2\theta )\lesssim {10}^{-6}$) sterile neutrino is still a viable dark matter candidate.

We point out a new and largely model-independent constraint on the dark matter scattering cross section with nucleons, which applies when this quantity is larger than for typical weakly interacting dark matter candidates. When the dark matter capture rate in Earth is efficient, the rate of energy deposition by dark matter self-annihilation products would grossly exceed the measured heat flow of Earth. This improves the spin-independent cross section constraints by many orders of magnitude and closes the window between astrophysical constraints (at very large cross sections) and underground detector constraints (at small cross sections). In the applicable mass range, from $\sim 1$ to $\sim {10}^{10}\mathrm{GeV}$, the scattering cross section of dark matter with nucleons is then bounded from above by the latter constraints and hence must be truly weak, as usually assumed.

The majority of fast millisecond pulsars are in binary systems, so that any periodic signal they emit is modulated by both Doppler and relativistic effects. Here we show how well-established binary models can be used to account for these effects in searches for gravitational waves from known pulsars within binary systems. A separate issue affecting certain pulsar signals is that of timing noise, and we show how this, with particular reference to the Crab pulsar, can be compensated for by using regularly updated timing ephemerides.

It has been recently argued that realistic models with warped extra dimensions can have Kaluza-Klein particles accessible at the CERN Large Hadron Collider if a custodial symmetry, $SU(2{)}_V\times P_{LR}$, is used to protect the $T$ parameter and the coupling of the left-handed bottom quark to the $Z$ gauge boson. In this article we emphasize that such a symmetry implies that the loop corrections to both the $T$ parameter and the $Z{b}_L{\overline{b}}_L$ coupling are calculable. In general, these corrections are correlated, can be sizable, and should be considered to determine the allowed parameter space region in models with warped extra dimensions and custodial symmetry, including Randall-Sundrum models with a fundamental Higgs, models of gauge-Higgs unification, and Higgsless models. As an example, we derive the constraints that arise on a representative model of gauge-Higgs unification from a global fit to the precision electroweak observables. A scan over the parameter space typically leads to a lower bound on the Kaluza-Klein excitations of the gauge bosons of about 2–3 TeV, depending on the configuration. In the fermionic sector one can have Kaluza-Klein excitations with masses of a few hundred GeV. We present the constraints on these light fermions from recent Tevatron searches, and explore interesting discovery channels at the LHC.

The estimation of rare $K$ decay matrix elements from $K_{\ell 3}$ experimental data is extended beyond LO in chiral perturbation theory. Isospin-breaking effects at next-to-leading order (and partially next-to-next-to-leading order) in the chiral perturbation theory expansion, as well as QED radiative corrections, are now accounted for. The analysis relies mainly on the cleanness of two specific ratios of form factors, for which the theoretical control is excellent. As a result, the uncertainties on the $K^{+}\to {\pi }^{+}\nu \overline{\nu }$ and $K_L\to {\pi }^0\nu \overline{\nu }$ matrix elements are reduced by a factor of about 7 and 4, respectively, and similarly for the direct $CP$-violating contributions to $K_L\to {\pi }^0{e}^{+}{e}^{-}$ and $K_L\to {\pi }^0{\mu }^{+}{\mu }^{-}$. They could be reduced even further with better experimental data for the $K_{\ell 3}$ slopes and the $K_{\ell 3}^{+}$ branching ratios. As a result, the nonparametric errors for $\mathcal{B}(K\to \pi \nu \overline{\nu })$ and for the direct $CP$-violating contributions to $\mathcal{B}(K_L\to {\pi }^0{\ell }^{+}{\ell }^{-})$ are now completely dominated by those on the short-distance physics.

It has been speculated that quantum-gravity might induce a foamy space-time structure at small scales, randomly perturbing the propagation phases of free-streaming particles (such as kaons, neutrons, or neutrinos). Particle interferometry might then reveal nonstandard decoherence effects, in addition to standard ones (due to, e.g., finite source size and detector resolution.) In this work we discuss the phenomenology of such nonstandard effects in the propagation of electron neutrinos in the Sun and in the long-baseline reactor experiment KamLAND, which jointly provide us with the best available probes of decoherence at neutrino energies $E\sim \mathrm{\text{few}}$ MeV. In the solar neutrino case, by means of a perturbative approach, decoherence is shown to modify the standard (adiabatic) propagation in matter through a calculable damping factor. By assuming a power-law dependence of decoherence effects in the energy domain ($E^n$ with $n=0$, $\pm 1$, $\pm 2$), theoretical predictions for two-family neutrino mixing are compared with the data and discussed. We find that neither solar nor KamLAND data show evidence in favor of nonstandard decoherence effects, whose characteristic parameter ${\gamma }_0$ can thus be significantly constrained. In the “Lorentz-invariant” case $n=-1$, we obtain the upper limit ${\gamma }_0<0.78\times {10}^{-26}\mathrm{GeV}$ at 95% C.L. In the specific case $n=-2$, the constraints can also be interpreted as bounds on possible matter density fluctuations in the Sun, which we improve by a factor of $\sim 2$ with respect to previous analyses.

We present measurements of the branching fractions for $B^0$-meson decays to ${\eta }^{\prime }{K}^0$ and $\omega K^0$, and of the branching fractions and $CP$-violation charge asymmetries for $B^{+}$-meson decays to $\eta {\pi }^{+}$, $\eta K^{+}$, ${\eta }^{\prime }{\pi }^{+}$, ${\eta }^{\prime }{K}^{+}$, $\omega {\pi }^{+}$, and $\omega K^{+}$. The data, collected with the BABAR detector at the Stanford Linear Accelerator Center, represent $383\times {10}^6$ $B\overline{B}$ pairs produced in $e^{+}{e}^{-}$ annihilation. The measurements agree with previous results; we find no evidence for direct $CP$ violation.

We study rigid string solutions rotating on the $S^3$ subspace of the $\beta$-deformed ${\mathrm{AdS}}_5\times S^5$ background found by Lunin and Maldacena. For particular values of the parameters of the solutions we find the known giant magnon and single spike strings. We present a single spike string solution on the deformed $S^3$ and find how the deformation affects the dispersion relation. The possible relation of this string solution to spin chains and the connection of the solutions on the undeformed $S^3$ to the sine-Gordon model are briefly discussed.

We study the effects of $\mathcal{O}({\alpha }_s)$ supersymmetric QCD (SQCD) corrections on the total production rate and kinematic distributions of polarized and unpolarized top-pair production in $pp$ and $p\overline{p}$ collisions. At the Fermilab Tevatron $p\overline{p}$ collider, top-quark pairs are mainly produced via quark-antiquark annihilation, $q\overline{q}\to t\overline{t}$, while at the CERN LHC $pp$ collider gluon-gluon scattering, $gg\to t\overline{t}$, dominates. We compute the complete set of $\mathcal{O}({\alpha }_s)$ SQCD corrections to both production channels and study their dependence on the parameters of the minimal supersymmetric standard model. In particular, we discuss the prospects for observing strong, loop-induced SUSY effects in top-pair production at the Tevatron run II and the LHC.

Generalized uncertainty relations are known to provide a minimal length $\hslash \sqrt{\beta }$. The effect of such minimal length in the Casimir-Polder interactions between neutral atoms (molecules) is studied. The first order correction term in the minimal uncertainty parameter is derived and found to describe an attractive potential scaling as $r^{-9}$, as opposed to the well-known $r^{-7}$ long range retarded potential.

Exact solutions with torsion in Einstein-Gauss-Bonnet gravity are derived. These solutions have a cross product structure of two constant curvature manifolds. The equations of motion give a relation for the coupling constants of the theory in order to have solutions with nontrivial torsion. This relation is not the Chern-Simons combination. One of the solutions has an ${\mathrm{AdS}}_2\times S^3$ structure and is so the purely gravitational analogue of the Bertotti-Robinson space-time where the torsion can be seen as the dual of the covariantly constant electromagnetic field.

We find a family of exact solutions of Einstein equations describing the field of a static axisymmetric thin disk living in six-dimensional space-time. In particular, we study the disks constructed (by cutting out the central part of the space-time) from the conventional Schwarzschild and Chazy-Curzon solutions with simple extensions in the extra 2 dimensions. The disks are interpreted in terms of two counterrotating streams of particles on free circular orbits. Two extra parameters—the constants of motion resulting from projections of the particle-velocities’ extra components—are constrained by the requirement that the orbits within the disk be stable. The requirement is met just in cases when the radial profile of the disk orbital speed fits the rotation curves of many spiral galaxies. It thus turns out that the effective modification of the gravity law by extra dimensions could explain the observed flatness of these curves equally well as the usual dark matter interpretation. In the second part of the paper we show that the inclusion of extra dimensions also leads to better fits of the gravitational lensing data for galaxy clusters, without changing results obtained in solar system scales. Finally, we discuss whether the effect of extra dimensions could also be translated as following from the occurrence of extra matter (“Kaluza-Klein particles”). A comment on possible properties of such particles and a chance to detect them at the CERN LHC is given in the Appendix.

We present the first calculation of the possible (local) cosmic string contribution to the cosmic microwave background polarization spectra from simulations of a string network (rather than a stochastic collection of unconnected string segments). We use field-theory simulations of the Abelian Higgs model to represent local U(1) strings, including their radiative decay and microphysics. Relative to previous estimates, our calculations show a shift in power to larger angular scales, making the chance of a future cosmic string detection from the B-mode polarization slightly greater. We explore a future ground-based polarization detector, taking the CLOVER project as our example. In the null hypothesis (that cosmic strings make a zero contribution) we find that CLOVER should limit the string tension $\mu$ to $G\mu <0.12\times {10}^{-6}$ (where $G$ is the gravitational constant), above which it is likely that a detection would be possible.

The best natural candidates for the realization of color superconductivity are quark stars—not yet confirmed by observation—and the extremely dense cores of compact stars, many of which have very large magnetic fields. To reliably predict astrophysical signatures of color superconductivity, a better understanding of the role of the star’s magnetic field in the color-superconducting phase that is realized in the core is required. This paper is an initial step in that direction. The field scales at which the different magnetic phases of a color superconductor with three quark flavors can be realized are investigated. Going from weak to strong fields, the system first undergoes a symmetry transmutation from a color-flavor-locked (CFL) phase to a magnetic-CFL (MCFL) phase, and then a phase transition from the MCFL phase to the paramagnetic-CFL (PCFL) phase. The low-energy effective theory for the excitations of the diquark condensate in the presence of a magnetic field is derived using a covariant representation that takes into account all the Lorentz structures contributing at low energy. The field-induced masses of the charged mesons and the threshold field at which the $\mathrm{CFL}\to \mathrm{MCFL}$ symmetry transmutation occurs are obtained in the framework of this low-energy effective theory. The relevance of the different magnetic phases for the physics of compact stars is discussed.

We present a new technique for time-domain numerical evolution of the scalar- field generated by a pointlike scalar charge orbiting a black hole. Time-domain evolution offers an efficient way for calculating black hole perturbations, especially as input for computations of the local self force acting on orbiting particles. In Kerr geometry, the field equations are not fully separable in the time domain, and one has to tackle them in $2+1$ dimensions (two spatial dimensions and time; the azimuthal dependence is still separable). A technical difficulty arises when the source of the field is a pointlike particle, as the $2+1$-dimensional perturbation is then singular: Each of the azimuthal modes diverges logarithmically at the particle. To deal with this problem we split the numerical domain into two regions: Inside a thin worldtube surrounding the particle’s worldline we solve for a regularized variable, obtained from the full field by subtracting out a suitable puncture function, given analytically. Outside this worldtube we solve for the full, original field. The value of the evolution variable is adjusted across the boundary of the worldtube. In this work we demonstrate the applicability of this method in the example of circular orbits around a Schwarzschild black hole (refraining from exploiting the spherical symmetry of the background, and working in $2+1$ dimensions).

A new constraint suppressing formulation of the Einstein evolution equations is presented, generalizing the five-parameter first-order system due to Kidder, Scheel, and Teukolsky (KST). The auxiliary fields, introduced to make the KST system first order, are given modified evolution equations designed to drive constraint violations toward zero. The algebraic structure of the new system is investigated, showing that the modifications preserve the hyperbolicity of the fundamental and constraint evolution equations. The evolution of the constraints for perturbations of flat spacetime is completely analyzed, and all finite-wavelength constraint modes are shown to decay exponentially when certain adjustable parameters satisfy appropriate inequalities. Numerical simulations of a single Schwarzschild black hole are presented, demonstrating the effectiveness of the new constraint-damping modifications.

We propose a Hamiltonian formalism for a generalized Friedmann-Robertson-Walker cosmology model in the presence of both a variable equation of state parameter $w(a)$ and a variable cosmological constant $\Lambda (a)$, where $a$ is the scale factor. This Hamiltonian system, containing 1 degree of freedom and without constraint, gives Friedmann equations as the equation of motion, which describes a mechanical system with a variable mass object moving in a potential field. After an appropriate transformation of the scale factor, this system can be further simplified to an object with constant mass moving in an effective potential field. In this framework, the $\Lambda$ cold dark matter model as the current standard model of cosmology corresponds to a harmonic oscillator. We further generalize this formalism to take into account the bulk viscosity and other cases. The Hamiltonian can be quantized straightforwardly, but this is different from the approach of the Wheeler-DeWitt equation in quantum cosmology.