We show that string theory on a compact negatively curved manifold, preserving a $U(1{)}^{b_1}$ winding symmetry, grows at least $b_1$ new effective dimensions as the space shrinks. The winding currents yield a “D-dual” description of a Riemann surface of genus $h$ in terms of its $2h$ dimensional Jacobian torus, perturbed by a closed string tachyon arising as a potential energy term in the world sheet sigma model. D-branes on such negatively curved manifolds also reveal this structure, with a classical moduli space consisting of a $b_1$-torus. In particular, we present an anti-de Sitter (AdS)/conformal field theory (CFT) system which offers a nonperturbative formulation of such supercritical backgrounds. Finally, we discuss generalizations of this new string duality.

We examine the dynamical behavior of recently introduced bubbles in asymptotically flat, five-dimensional spacetimes. Using numerical methods, we find that even bubbles that initially start expanding eventually collapse to a Schwarzschild-Tangherlini black hole.

We employ the string/gauge theory correspondence to study properties of strongly coupled quark-gluon plasmas in thermal gauge theories with a large number of colors and flavors. In particular, we analyze noncritical string duals of conformal (S)QCD, as well as ten-dimensional wrapped fivebrane duals of SQCD-like theories. We study general properties of the dual plasmas, including the drag force exerted on a probe quark and the jet quenching parameter. We find that these plasma observables depend on the number of colors and flavors in the “QCD dual”; in particular, we find that the jet quenching parameter increases linearly with $N_f/N_c$ at leading order in the probe limit. In the ten-dimensional case we find a nontrivial drag coefficient but a vanishing jet quenching parameter. We comment on the relation of this result with total screening and argue that the same features are shared by all known plasmas dual to fivebranes in ten dimensions. We also construct new D5 black hole solutions with spherical horizon and show that they exhibit the same features.

We investigate unparticle effects in $B_s$-${\overline{B}}_s$ mixing. In particular we discuss the possibility of reproducing the experimental result of $\Delta M_s$, while having large effects on the mixing phase ${\varphi }_s$, which might be visible in current experiments.

We argue that supersymmetric flat direction vacuum expectation values can decay nonperturbatively via preheating. Considering a toy $U(1)$ gauge theory, we explicitly calculate the scalar potential, in the unitary gauge, for excitations around several flat directions. We show that the mass matrix for the excitations has nondiagonal entries which vary with the phase of the flat direction vacuum expectation value. Furthermore, this mass matrix has zero eigenvalues whose eigenstates change with time. We show that these light degrees of freedom are produced copiously in the nonperturbative decay of the flat direction vacuum expectation value.

We present a new stationary, asymptotically flat solution of 5D Einstein-Maxwell gravity describing a Saturn-like black object: a rotating black hole surrounded by a rotating dipole black ring. The solution is generated by combining the vacuum black Saturn solution and the vacuum black ring solution with appropriately chosen parameters. Some basic properties of the solution are analyzed and the basic quantities are calculated.

In this paper we elaborate on the relation between the entropy formula of Wald and the “entropy function” method proposed by Sen. For spherically symmetric extremal black holes, it is shown that the expression of extremal black hole entropy given by Sen can be derived from the general entropy definition of Wald, without the help of the treatment of rescaling the ${\mathrm{AdS}}_2$ part of the near horizon geometry of extremal black holes. In our procedure, we only require that the surface gravity approaches to zero, and it is easy to understand the Legendre transformation of $f$, the integration of Lagrangian density on the horizon, with respect to the electric charges. Since the Noether charge form can be defined in an “off-shell” form, we define a corresponding entropy function, with which one can discuss the attractor mechanism for extremal black holes with scalar fields.

We investigate the braneworld model with induced gravity to clarify the role of the crossover length scale $\ell$ in the possible explanation of the dark-matter phenomenon in astrophysics and in cosmology. Observations of the 21 cm line from neutral hydrogen clouds in spiral galaxies reveal that the rotational velocities remain nearly constant at a value ${\upsilon }_c\sim {10}^{-3}–{10}^{-4}$ in the units of the speed of light in the region of the galactic halo. Using the smallness of ${\upsilon }_c$, we develop a perturbative scheme for reconstructing the metric in a galactic halo. In the leading order of expansion in ${\upsilon }_c$, at the distances $r\gtrsim {\upsilon }_c\ell$, our result reproduces that obtained in the Randall-Sundrum braneworld model. This inequality is satisfied in a real spiral galaxy such as our Milky Way for distances $r\sim 3\mathrm{kpc}$, at which the rotational velocity curve becomes flat, ${\upsilon }_c\sim 7\times {10}^{-4}$, if $\ell \lesssim 2\mathrm{Mpc}$. The gravitational situation in this case can be approximately described by the Einstein equations with the so-called Weyl fluid playing the role of dark matter. In the region near the gravitating body, we derive a closed system of equations for the static spherically symmetric situation under the approximation of zero anisotropic stress of the Weyl fluid. We find the Schwarzschild metric to be an approximate vacuum solution of these equations at distances $r\lesssim \sqrt[3]{r_g{\ell }^2}$. The value $\ell \lesssim 2\mathrm{Mpc}$ complies well with the solar system tests. At the same time, in cosmology, a low-density braneworld with $\ell$ of this order of magnitude can mimic the expansion properties of the high-density $\Lambda +\mathrm{\text{cold dark matter}}$ (LCDM) universe at late times. Combined observations of galactic rotation curves and gravitational lensing can possibly discriminate between the higher-dimensional effects and dark matter.

Using nonperturbative results obtained recently for a uniformly accelerated Unruh-DeWitt detector, we discover new features in the dynamical evolution of the detector’s internal degree of freedom, and identified the Unruh effect derived originally from time-dependent perturbation theory as operative in the ultraweak coupling and ultrahigh acceleration limits. The mutual interaction between the detector and the field engenders entanglement between them, and tracing out the field leads to a mixed state of the detector even for a detector at rest in Minkowski vacuum. Our findings based on this exact solution show clearly the differences from the ordinary result where the quantum field’s backreaction is ignored in that the detector no longer behaves like a perfect thermometer. From a calculation of the evolution of the reduced density matrix of the detector, we find that the transition probability from the initial ground state over an infinitely long duration of interaction derived from time-dependent perturbation theory is existent in the exact solution only in transient under special limiting conditions corresponding to the Markovian regime. Furthermore, the detector at late times never sees an exact Boltzmann distribution over the energy eigenstates of the free detector, thus in the non-Markovian regime covering a wider range of parameters the Unruh temperature cannot be identified inside the detector.

To study noncommutativity properties of the open string with constant $B$ field, we construct a mechanical action that reproduces classical dynamics of the string sector under consideration. It allows one to apply the Dirac quantization procedure for constrained systems in a direct and unambiguous way. The mechanical action turns out to be the first order system without taking the strong field limit $B\to \infty$. In particular, it is true for the zero mode of the string coordinate, which means that the noncommutativity is an intrinsic property of this mechanical system. We describe the arbitrariness in the relation existing between the mechanical and the string variables and show that noncommutativity of the string variables on the boundary can be removed. This is in correspondence with the result of Seiberg and Witten on the relation among noncommutative and ordinary Yang-Mills theories. The recently developed soldering formalism helps us to establish a connection between the original open string action and the Polyakov action.

We consider the cosmological models for the higher dimensional space-time which includes the curvatures of our space as well as the curvatures of the internal space. We find that the condition for the integrability of the cosmological equations is that the total space-time dimensions are $D=10$ or $D=11$ which is exactly the conditions for superstrings or M theory. We obtain analytic solutions with generic initial conditions in the four-dimensional Einstein frame and study the accelerating universe when both our space and the internal space have negative curvatures.

We apply the technique of parameter splitting to existing cosmological data sets, to check for a generic failure of dark energy models. Given a dark energy parameter, such as the energy density ${\Omega }_{\Lambda }$ or equation of state $w$, we split it into two meta-parameters with one controlling geometrical distances, and the other controlling the growth of structure. Observational data spanning Type Ia Supernovae, the cosmic microwave background (CMB), galaxy clustering, and weak gravitational lensing statistics are fit without requiring the two meta-parameters to be equal. This technique checks for inconsistency between different data sets, as well as for internal inconsistency within any one data set (e.g., CMB or lensing statistics) that is sensitive to both geometry and growth. We find that the cosmological constant model is consistent with current data. Theories of modified gravity generally predict a relation between growth and geometry that is different from that of general relativity. Parameter splitting can be viewed as a crude way to parametrize the space of such theories. Our analysis of current data already appears to put sharp limits on these theories: assuming a flat universe, current data constrain the difference $\Delta {\Omega }_{\Lambda }={\Omega }_{\Lambda }(\mathrm{geom})-{\Omega }_{\Lambda }(\mathrm{grow})$ to be $-{0.0044}_{-0.0057-0.0119}^{+0.0058+0.0108}$ (68% and 95% C.L. respectively); allowing the equation of state $w$ to vary, the difference $\Delta w=w(\mathrm{geom})-w(\mathrm{grow})$ is constrained to be ${0.37}_{-0.36-0.53}^{+0.37+1.09}$. Interestingly, the region $w(\mathrm{grow})>w(\mathrm{geom})$, which should be generically favored by theories that slow structure formation relative to general relativity, is quite restricted by data already. We find $w(\mathrm{grow})<-0.80$ at $2\sigma$. As an example, the best-fit flat Dvali-Gabadadze-Porrati model approximated by our parametrization lies beyond the $3\sigma$ contour for constraints from all the data sets.

In the present work, we investigate the universe dominated by quintom or hessence energies in loop quantum cosmology (LQC). Interestingly enough, we find that there are some stable attractors in these two cases. In the case of quintom, all stable attractors have the feature of decelerated expansion. In the case of hessence, most of stable attractors have the feature of decelerated expansion while one stable attractor can have decelerated or accelerated expansion depend on the model parameter. In all cases, the equation-of-state parameter (EoS) of all stable attractors are larger than $-1$ and there is no singularity in the finite future. These results are different from the dynamics of phantom in LQC, or the ones of phantom, quintom, and hessence in classical Einstein gravity.

Models of late-time neutrino mass generation contain new interactions of the cosmic background neutrinos with supernova relic neutrinos (SRNs). Exchange of an on-shell light scalar may lead to significant modification of the differential SRN flux observed at earth. We consider an Abelian U(1) model for generating neutrino masses at low scales, and show that there are cases for which the changes induced in the flux allow one to distinguish the Majorana or Dirac nature of neutrinos, as well as the type of neutrino mass hierarchy (normal or inverted or quasidegenerate). In some region of parameter space the determination of the absolute values of the neutrino masses is also conceivable. Measurements of the presence of these effects may be possible at the next-generation water Cerenkov detectors enriched with Gadolinium, or a 100 kton liquid argon detector.

In this paper, we test the original holographic dark energy model with some old high redshift objects. The main idea is very simple: the universe cannot be younger than its constituents. We find that the original holographic dark energy model can be ruled out, unless a lower Hubble constant is taken.

We evaluate the partial widths for internal conversions in the Higgs decays to two photons. For the Higgs masses of interest at the CERN LHC in the range of 100–150 GeV, the conversions to pairs of fermions represent a significant fraction of Higgs decays.

The nonrelativistic $G_{0}G$ formalism of BCS-BEC crossover at finite temperature is extended to relativistic fermion systems. The uncondensed pairs contribute a pseudogap to the fermion excitations. The theory recovers the BCS mean field approximation at zero temperature and the nonrelativistic results in a proper limit. For massive fermions, when the coupling strength increases, there exist two crossovers from the weak coupling BCS superfluid to the nonrelativistic BEC state and then to the relativistic BEC state. For color superconductivity at moderate baryon density, the matter is in the BCS-BEC crossover region, and the behavior of the pseudogap is quite similar to that found in high temperature superconductors.

Low-energy phenomenology of the unparticle physics associated with an exact scale invariant sector possessing a nontrivial infrared fixed point at a higher energy scale is explored for both electron-positron and hadronic colliders. Feynman rules for a spin 0, 1, or 2 unparticle coupled to a variety of standard model gauge invariant operators that are relevant to many low-energy processes involving either real emissions of unparticles or their virtual propagator effects are presented. Missing energy and/or recoil mass distributions of the unparticle in the associated production of the unparticle together with a photon or $Z$ boson at LEP2 and ILC as well as in $Z$ decay into an unparticle plus a fermion-antifermion pair are studied. In addition, monojet production with missing energy from the unparticle at hadronic collisions are explored. The complex phase in the unparticle propagator that can give rise to interesting interference effects between an unparticle-exchange diagram and the standard model amplitudes are studied in details for the Drell-Yan process as well as muon pair and diphoton production in electron-positron annihilation. These energy and/or recoil mass distributions (with the exception in hadron colliders) and interference effects are found sensitively depending not only on the scaling dimension but also on the spin of the unparticle. For the spin-2 unparticle, its physical effects are found to resemble that of a tower of Kaluza-Klein gravitons, which strongly indicates that the underlying unparticle physics may have root in a higher dimensional theory. A connection between unparticle physics and theories of large extra dimensions is speculated. Experimental constraints on the unparticle scale are deduced from the LEP2 data on monophoton production and from the 4-fermion contact interactions.

Radiative decays $\varphi \to \eta {\pi }^0\gamma$ and $\varphi \to {\pi }^0{\pi }^0\gamma$ are studied assuming that these decays are caused through the intermediate $a_0(980)\gamma$ and $f_0(980)\gamma$ states, respectively. Fitting the experimental data of the $\eta {\pi }^0$ and ${\pi }^0{\pi }^0$ invariant mass spectrum in the decays $\varphi \to \eta {\pi }^0\gamma$ and ${\pi }^0{\pi }^0\gamma$, it is shown that the processes $\varphi \to a_0\gamma$ and $\varphi \to f_0\gamma$ are dominated by the $K^{+}{K}^{-}$ loop interaction rather than the pointlike $\varphi a_0(f_0)\gamma$ one both for the nonderivative and derivative $SPP$ coupling. The experimental data of $\Gamma [\varphi \to f_0\gamma ]/\Gamma [\varphi \to a_0\gamma ]$ predicts that $g_{f_{0}K\overline{K}}/g_{a_{0}K\overline{K}}\sim 2$. Considering the effects of the mixing between low mass scalar $qq\overline{q}\overline{q}$ states and high mass scalar $q\overline{q}$ states to these coupling constants $g_{f_{0}K\overline{K}}$ and $g_{a_{0}K\overline{K}}$, one suggests that this mixing is rather large.

We report on a new measurement of the branching ratio $\mathrm{B}(K_L\to {\pi }^0{e}^{+}{e}^{-}\gamma )$ using the KTeV detector. This analysis uses the full KTeV data set collected from 1997 to 2000. We reconstruct 139 events over a background of 14, which results in $\mathrm{B}(K_L\to {\pi }^0{e}^{+}{e}^{-}\gamma )=(1.62\pm {0.14}_{\mathrm{stat}}\pm {0.09}_{\mathrm{syst}})\times {10}^{-8}$. This result supersedes the earlier KTeV measurement of this branching ratio.