We analyze the quantum description of a free scalar field on the circle in the presence of an explicitly time-dependent potential, also interpretable as a time-dependent mass. Classically, the field satisfies a linear wave equation of the form $\ddot{\xi }-{\xi }^{\prime \prime }+f(t)\xi =0$. We prove that the representation of the canonical commutation relations corresponding to the particular case of a massless free field ($f=0$) provides a unitary implementation of the dynamics for sufficiently general mass terms, $f(t)$. Furthermore, this representation is uniquely specified, among the class of representations determined by $S^1$-invariant complex structures, as the only one allowing a unitary dynamics. These conclusions can be extended in fact to fields on the two-sphere possessing axial symmetry. This generalizes a uniqueness result previously obtained in the context of the quantum field description of the Gowdy cosmologies, in the case of linear polarization and for any of the possible topologies of the spatial sections.

The anomaly cancellation method proposed by Wilczek et al. is applied to the general charged rotating black holes in five-dimensional minimal gauged supergravity. Thus Hawking temperature and fluxes are found. The Hawking temperature obtained agrees with the surface gravity formula. The black holes have charge and two unequal angular momenta, and these give rise to appropriate terms in the effective U(1) gauge field of the reduced ($1+1$)-dimensional theory. In particular, it is found that the terms in this U(1) gauge field correspond exactly to the correct electrostatic potential and the two angular velocities on the horizon of the black holes, and so the results for the Hawking fluxes derived here from the anomaly cancellation method are in complete agreement with the ones obtained from integrating the Planck distribution.

We study the mechanics of $D$-dimensional isolated horizons (IHs) for Einstein gravity in the presence of arbitrary $p$-form matter fields. This generalizes the analysis of Copsey and Horowitz to nonstationary spacetimes and therefore the local first law in $D>4$ dimensions to include nonmonopolar (dipole) charges. The only requirement for the local first law to hold is that the action has to be differentiable. The resulting conserved charges are all intrinsic to the horizon and are independent of the topology of the horizon cross sections. We explicitly calculate the local charges for five-dimensional black holes and black rings that are relevant within the context of superstring theory. We conclude with some comments on the black-hole/string correspondence principle and argue that IHs (or some other quasilocal variant) should play a fundamental role in superstring theory.

The “improved dynamics” of loop quantum cosmology is extended to include anisotropies of the Bianchi type I model. As in the isotropic case, a massless scalar field serves as a relational time parameter. However, the extension is nontrivial because one has to face several conceptual subtleties as well as technical difficulties. These include a better understanding of the relation between loop quantum gravity and loop quantum cosmology, handling novel features associated with the nonlocal field strength operator in presence of anisotropies, and finding dynamical variables that make the action of the Hamiltonian constraint manageable. Our analysis provides a conceptually complete description that overcomes limitations of earlier works. We again find that the big-bang singularity is resolved by quantum geometry effects but, because of the presence of Weyl curvature, Planck scale physics is now much richer than in the isotropic case. Since the Bianchi I models play a key role in the Belinskii, Khalatnikov, Lifshitz conjecture on the nature of generic spacelike singularities in general relativity, the quantum dynamics of Bianchi I cosmologies is likely to provide considerable intuition about the fate of generic spacelike singularities in quantum gravity. Finally, we show that the quantum dynamics of Bianchi I cosmologies projects down exactly to that of the Friedmann model. This opens a new avenue to relate more complicated models to simpler ones, thereby providing a new tool to relate the quantum dynamics of loop quantum gravity to that of loop quantum cosmology.

We study cosmologies in modified theories of gravity considering Lagrangian density $f(R)$ which is a polynomial function of scalar curvature $(R)$ in the Einstein-Hilbert action in vacuum. The field equation obtained from the modified action corresponding to a Robertson-Walker metric is highly nonlinear and not simple enough to obtain analytic solution. Consequently we adopt a numerical technique to study the evolution of the Friedmann-Robertson-Walker universe. A number of evolutionary phases of the Universe including the present accelerating phase are found to exist in the higher derivative theories of gravity. The cosmological solutions obtained here are new and interesting. We study a modified theory of gravity as a toy model to explore the past and the present, and to predict the future evolution. It is found that all the models analyzed here can reproduce the current accelerating phase of expansion of the Universe. The duration of the present accelerating phase is found to depend on the coupling constants of the gravitational action. The physical importance of the coupling parameters considered in the action are also discussed.

We compare the sensitivity of a recent bound on time variation of the fine structure constant from optical clocks with bounds on time-varying fundamental constants from atomic clocks sensitive to the electron-to-proton mass ratio, from radioactive decay rates in meteorites, and from the Oklo natural reactor. Tests of the weak equivalence principle also lead to comparable bounds on present variations of constants. The “winner in sensitivity” depends on what relations exist between the variations of different couplings in the standard model of particle physics, which may arise from the unification of gauge interactions. Weak equivalence principle tests are currently the most sensitive within unified scenarios. A detection of time variation in atomic clocks would favor dynamical dark energy and put strong constraints on the dynamics of a cosmological scalar field.

Cosmic strings can be created in the early universe during symmetry-breaking phase transitions, such as might arise if the gauge structure of the standard model is extended by additional $U(1)$ factors at high energies. Cosmic strings presented in the early universe form a network of long horizon-length segments, as well as a population of closed string loops. The closed loops are unstable against decay, and can be a source of nonthermal particle production. In this work we compute the density of weakly-interacting massive particle dark matter formed by the decay of gauge theory cosmic string loops derived from a network of long strings in the scaling regime or under the influence of frictional forces. We find that for symmetry-breaking scales larger than ${10}^{10}\mathrm{GeV}$, this mechanism has the potential to account for the observed relic density of dark matter. For symmetry-breaking scales lower than this, the density of dark matter created by loop decays from a scaling string network lies below the observed value. In particular, the cosmic strings originating from a $U(1)$ gauge symmetry broken near the electroweak scale, that could lead to a massive $Z^{\prime }$ gauge boson observable at the LHC, produces a negligibly small dark matter relic density by this mechanism.

In this work, we consider a braneworld model with a timelike extra dimension. There are strong constraints to the parameter values of such a model resulting from the claim that there must be a physical solution to the Friedmann equation at least between now and the time of recombination. We fitted the model to supernova type Ia data and checked the consistency of the result with other observations. For parameter values that are consistent with observations, the braneworld model is indistinguishable from a $\Lambda \mathrm{CDM}$ universe as far as the considered cosmological tests are concerned.

The Greisen-Zatsepin-Kuzmin cutoff predicted at the ultrahigh energy cosmic ray spectrum has been observed by the HiRes and Auger experiments. The results put severe constraints on the effect of Lorentz invariance violation (LIV), which has been introduced to explain the absence of the Greisen-Zatsepin-Kuzmin cutoff indicated in the AGASA data. Assuming a homogeneous source distribution with a single power-law spectrum, we calculate the ultrahigh energy cosmic ray spectrum observed on the Earth by taking photopion production, $e^{+}{e}^{-}$ pair production, and the adiabatic energy loss into account. The effect of LIV is also taken into account in the calculation. By fitting the HiRes monocular spectra and the Auger combined spectra, we show that the LIV parameter is constrained to $\xi =-{0.8}_{-0.5}^{+3.2}\times {10}^{-23}$ and ${0.0}_{-0.4}^{+1.0}\times {10}^{-23}$, respectively, which is very consistent with strict Lorentz invariance up to the highest energy.

We reconstruct an explicit model of modified gravity in which a crossing of the phantom divide can be realized. It is shown that the (finite-time) Big Rip singularity appears in the model of modified gravity (i.e., in the so-called Jordan-frame), whereas that in the corresponding scalar field theory obtained through the conformal transformation (i.e., in the so-called Einstein frame) the singularity becomes the infinite-time one. Furthermore, we investigate the relations between the scalar field theories with realizing a crossing of the phantom divide and the corresponding modified gravitational theories by using the inverse conformal transformation. It is demonstrated that the scalar field theories describing the nonphantom phase (phantom one with the Big Rip) can be represented as the theories of real (complex) $F(R)$ gravity through the inverse (complex) conformal transformation. We also study a viable model of modified gravity in which the transition from the de Sitter universe to the phantom phase can occur. In addition, we explore the stability for the obtained solutions of the crossing of the phantom divide under a quantum correction coming from conformal anomaly.

The precision obtainable in phenomenological applications of chiral perturbation theory is currently limited by our lack of knowledge on the low-energy constants (LECs). The assumption that the most important contributions to the LECs come from the dynamics of the low-lying resonances, often referred to as the resonance saturation hypothesis, has stimulated the use of large-$N_C$ resonance Lagrangians in order to obtain explicit values for the LECs. We study the validity of the resonance saturation assumption at the next-to-leading order in the $1/N_C$ expansion within the framework of resonance chiral theory. We find that, by imposing QCD short-distance constraints, the chiral couplings can be written in terms of the resonance masses and couplings and do not depend explicitly on the coefficients of the chiral operators in the Goldstone boson sector of resonance chiral theory. As we argue, this is the counterpart formulation of the resonance saturation statement in the context of the resonance Lagrangian. Going beyond leading order in the $1/N_C$ counting allows us to keep full control of the renormalization scale dependence of the LEC estimates.

In this paper we explore the constraints from $B$-physics observables in supersymmetric models of minimal flavor violation, in the large $\tan \beta$ regime, for both low and high-scale supersymmetry breaking scenarios. We find that the rare $B$-decays $b\to s\gamma$ and $B_s\to {\mu }^{+}{\mu }^{-}$ can be quite sensitive to the scale $M$ at which supersymmetry breaking is communicated to the visible sector. In the case of high scale supersymmetry breaking, we show that the additional gluino contribution to the $b\to s\gamma$ and $B_s\to {\mu }^{+}{\mu }^{-}$ rare decay rates can be significant for large $\tan \beta$, $\mu$ and $M_3$. The constraints on $B_u\to \tau \nu$ are relatively insensitive to the precise scale of $M$. We also consider the additional constraints from the present direct Higgs searches at the Tevatron in the inclusive $H/A\to \tau \tau$ channel, and the latest Cryogenic Dark Matter Search direct dark matter detection experiments. We find that altogether the constraints from $B$-physics, Higgs physics, and direct dark matter searches can be extremely powerful in probing regions of supersymmetric parameter space for low $M_A$ and large $\tan \beta$, leading to a preference for models with a lightest $CP$-even Higgs mass close to the current experimental limit. We find interesting regions of parameter space that satisfy all constraints and can be probed by Higgs searches at the Tevatron and the LHC and by direct dark matter searches in the near future.

Heavy, as yet undiscovered particles, can affect measurements of $CP$ violation in the $B$ system. Measuring $CP$ violation in the $B_s$ system provides an excellent place to observe such effects since standard model sources are predicted to produce very small effects. The angle $-2{\beta }_s$, the “phase of $B_s-{\overline{B}}_s$ mixing,” thought to be best measured in $B_s\to J/\psi \varphi$ decays is of order $-0.04$, while the $CP$ violating asymmetry in $B_s\to \varphi \varphi$ is predicted to be zero, due to the cancellation of the mixing phase with the decay phase. Recent measurements of ${\beta }_s$ in $J/\psi \varphi$, while not definitive, are much larger than the standard model predictions. Measurements in the $B^0$ and $D_s^{+}$ systems of analogous modes point toward a 5–10% contamination of S-wave $K^{+}{K}^{-}$ under the $\varphi$ peak. This S-wave was not taken into account in these recent analyses. Furthermore this S-wave can also materialize as a $f_0(980)$ meson that decays to ${\pi }^{+}{\pi }^{-}$, making the final state $J/\psi f_0$ useful for measuring ${\beta }_s$ with the added advantage of not requiring an angular analysis. Rate estimates, while not precise, predict four to five times fewer such events than those in the $J/\psi \varphi$ mode. The error on ${\beta }_s$, however, may be similar. We also remark on S-wave problems with the $B_s\to \varphi \varphi$ mode, and possible systematic checks using $B_s\to \varphi f_0$.

We present updated measurements of time-dependent $CP$ asymmetries in fully reconstructed neutral $B$ decays containing a charmonium meson. The measurements reported here use a data sample of $(465\pm 5)\times {10}^6$ $\mathit{{\rm Y}}(4S)\to B\overline{B}$ decays collected with the BABAR detector at the PEP-II asymmetric energy $e^{+}{e}^{-}$ storage rings operating at the SLAC National Accelerator Laboratory. The time-dependent $CP$ asymmetry parameters measured from $J\psi K_S^0$, $J\psi K_L^0$, $\psi (2S)K_S^0$, ${\eta }_c{K}_S^0$, ${\chi }_{c1}{K}_S^0$, and $J/\psi K^{*}(892{)}^0$ decays are: $C_f=0.024\pm 0.020(\mathrm{stat})\pm 0.016(\mathrm{syst})$ and $-{\eta }_f{S}_f=0.687\pm 0.028(\mathrm{stat})\pm 0.012(\mathrm{syst})$.

We propose an all-digital telescope for 21 cm tomography, which combines key advantages of both single dishes and interferometers. The electric field is digitized by antennas on a rectangular grid, after which a series of fast Fourier transforms recovers simultaneous multifrequency images of up to half the sky. Thanks to Moore’s law, the bandwidth up to which this is feasible has now reached about 1 GHz, and will likely continue doubling every couple of years. The main advantages over a single dish telescope are cost and orders of magnitude larger field-of-view, translating into dramatically better sensitivity for large-area surveys. The key advantages over traditional interferometers are cost (the correlator computational cost for an $N$-element array scales as $N{log}_{2}N$ rather than $N^2$) and a compact synthesized beam. We argue that 21 cm tomography could be an ideal first application of a very large fast Fourier transform telescope, which would provide both massive sensitivity improvements per dollar and mitigate the off-beam point source foreground problem with its clean beam. Another potentially interesting application is cosmic microwave background polarization.

The diffuse supernova neutrino background (DSNB) provides an immediate opportunity to study the emission of MeV thermal neutrinos from core-collapse supernovae. The DSNB is a powerful probe of stellar and neutrino physics, provided that the core-collapse rate is large enough and that its uncertainty is small enough. To assess the important physics enabled by the DSNB, we start with the cosmic star formation history of Hopkins and Beacom (2006) and confirm its normalization and evolution by cross-checks with the supernova rate, extragalactic background light, and stellar mass density. We find a sufficient core-collapse rate with small uncertainties that translate into a variation of $\pm 40\%$ in the DSNB event spectrum. Considering thermal neutrino spectra with effective temperatures between 4–6 MeV, the predicted DSNB is within a factor 4–2 below the upper limit obtained by Super-Kamiokande in 2003. Furthermore, detection prospects would be dramatically improved with a gadolinium-enhanced Super-Kamiokande: the backgrounds would be significantly reduced, the fluxes and uncertainties converge at the lower threshold energy, and the predicted event rate is $1.2–5.6\mathrm{events}{\mathrm{yr}}^{-1}$ in the energy range 10–26 MeV. These results demonstrate the imminent detection of the DSNB by Super-Kamiokande and its exciting prospects for studying stellar and neutrino physics.

We investigate the potential of the compact muon solenoid detector at the CERN Large Hadron Collider (LHC) to discriminate between two theoretical models predicting anomalous events with jets and large missing transverse energy, minimal supersymmetry, and little Higgs with $T$ parity. We focus on a simple test-case scenario, in which the only exotic particles produced at the LHC are heavy color-triplet states (squarks or $T$ quarks), and the only open decay channel for these particles is into the stable missing-energy particle (neutralino or heavy photon) plus a quark. We find that in this scenario, the angular and momentum distributions of the observed jets are sufficient to discriminate between the two models with a few inverse femtobarns of the LHC data, provided that these distributions for both models and the dominant standard model backgrounds can be reliably predicted by Monte Carlo simulations.

We discuss the holographic derivation of the magnetic susceptibility of the quark condensate. It is found that the susceptibility emerges upon the account of the Chern-Simons term in the holographic action. We demonstrate that Vainshtein’s relation is not exact in the hard wall dual model but is fulfilled with high accuracy. Some comments concerning the spectral density of the Dirac operator are presented.

We study the supersymmetry generators $Q$, $S$ on the 1-loop vectorless sector of $\mathcal{N}=4$ super Yang-Mills theory, by reduction to the plane-wave matrix model. Using a coherent basis in the $\mathfrak{s}\mathfrak{u}(2\mid 2)$ sector, a comparison with the algebra given by Beisert is presented, and some parameters (up to one loop) are determined. We make a final comparison of these supercharges with the results that can be obtained from the string action by working in the light-cone gauge and discretizing the string.

We study $n$-point boundary correlation functions in timelike boundary Liouville theory, relevant for open string multiproduction by a decaying unstable $D$ brane. We give an exact result for the one-point function of the tachyon vertex operator and show that it is consistent with a previously proposed relation to a conserved charge in string theory. We also discuss when the one-point amplitude vanishes. Using a straightforward perturbative expansion, we find an explicit expression for a tachyon $n$-point amplitude for all $n$, however the result is still a toy model. The calculation uses a new asymptotic approximation for Toeplitz determinants, derived by relating the system to a Dyson gas at finite temperature.