We demonstrate how to construct purely metric modifications of gravity which agree with general relativity in the weak field regime appropriate to the Solar System, but which possess an ultra-weak field regime when the gravitational acceleration becomes comparable to $a_0\sim {10}^{-10}\mathrm{m}/{\mathrm{s}}^2$. In this ultra-weak field regime, the models reproduce the MOND force without dark matter and also give enough gravitational lensing to be consistent with existing data. Our models are nonlocal and might conceivably derive from quantum corrections to the effective field equations.

We propose a new propagation formula for the Maxwell field in de Sitter space which exploits the conformal invariance of this field together with a conformal gauge condition. This formula allows to determine the classical electromagnetic field in the de Sitter space from given currents and initial data. It only uses the Green’s function of the massless Minkowskian scalar field. This leads to drastic simplifications in practical calculations. We apply this formula to the classical problem of the two charges of opposite signs at rest at the North and South Poles of the de Sitter space.

One of the solutions to the cosmological Polonyi problem is to introduce a large coupling between the Polonyi field and the inflaton so that the Polonyi field adiabatically tracks the temporal minimum of the potential. We study general conditions for the adiabatic suppression mechanism to work, and find that a non-negligible amount of the Polonyi field is induced in the form of coherent oscillations at the end of inflation. In the case of low reheating temperature, this contribution is so small that it does not cause cosmological problems. On the other hand, this contribution may be significant for a relatively high reheating temperature and we still need some amount of tuning in order to avoid the Polonyi problem. We also point out that Polonyi particles produced from thermal plasma pose a severe constraint on the reheating temperature. Furthermore, we extend the original framework to include enhanced couplings of the Polonyi field with the visible particles as well as with itself, and derive upper bounds on the reheating temperature after inflation. We also investigate the adiabatic solution to the cosmological moduli problem in gauge and anomaly mediation.

We perform an analysis of the recent WMAP7 data considering physically motivated and viable reionization scenarios with the aim of assessing their effects on cosmological parameter determinations. The main novelties are: (i) the combination of cosmic microwave background data with astrophysical results from quasar absorption line experiments; (ii) the joint variation of both the cosmological and astrophysical [governing the evolution of the free electron fraction $x_e(z)$] parameters. Including a realistic, data-constrained reionization history in the analysis induces appreciable changes in the cosmological parameter values deduced through a standard WMAP7 analysis. Particularly noteworthy are the variations in ${\Omega }_b{h}^2={0.02258}_{-0.00056}^{+0.00057}$ [WMAP7 (Sudden)] vs ${\Omega }_b{h}^2=0.02183\pm 0.00054$ [$\mathrm{WMAP}7+\mathrm{ASTRO}$ (CF)] and the new constraints for the scalar spectral index, for which $\mathrm{WMAP}7+\mathrm{ASTRO}$ (CF) excludes the Harrison-Zel’dovich value $n_s=1$ at $>3\sigma$. Finally, the electron-scattering optical depth value is considerably decreased with respect to the standard WMAP7, i.e. ${\tau }_e=0.080\pm 0.012$. We conclude that the inclusion of astrophysical data sets, allowing to robustly constrain the reionization history, in the extraction procedure of cosmological parameters leads to relatively important differences in the final determination of their values.

We find a new set of the Bianchi type I power-law expanding solutions in a string-motivated Dirac-Born-Infeld theory. Stability analysis shows that these power-law inflationary solutions remain stable with or without the contribution of the Dirac-Born-Infeld effect. We also find a new set of Bianchi type I expanding power-law solutions in a two scalar Dirac-Born-Infeld model with an additional phantom field. It is shown that the inclusion of the phantom field turns the Bianchi type I power-law solutions unstable during the inflationary phase.

Combined analyses of recent cosmological data are showing interesting hints for the presence of an extra relativistic component, coined dark radiation. Here, we perform a new search for dark radiation, parametrizing it with an effective number of relativistic degrees of freedom parameter, $N_{\mathrm{eff}}$. We show that the cosmological data we considered are clearly suggesting the presence of an extra relativistic component with $N_{\mathrm{eff}}={4.08}_{-0.68}^{+0.71}$ at 95% C.L.. Performing an analysis on dark radiation sound speed $c_{\mathrm{eff}}$ and viscosity $c_{\mathrm{vis}}$ parameters, we found $c_{\mathrm{eff}}^2=0.312\pm 0.026$ and $c_{\mathrm{vis}}^2={0.29}_{-0.16}^{+0.21}$ at 95% C.L., consistent with the expectations of a relativistic free streaming component ($c_{\mathrm{eff}}^2=c_{\mathrm{vis}}^2=1/3$). Assuming the presence of 3 relativistic neutrinos, we constrain the extra relativistic component with $N_{\nu }^S={1.10}_{-0.72}^{+0.79}$ and $c_{\mathrm{eff}}^2={0.24}_{-0.13}^{+0.08}$ at 95% C.L. while $c_{\mathrm{vis}}^2$ results as unconstrained. Assuming a massive neutrino component, we obtain further indications for dark radiation with $N_{\nu }^S={1.12}_{-0.74}^{+0.86}$ at 95% C.L..

The search for gravitational-wave signals in detector data is often hampered by the fact that many data analysis methods are based on the theory of stationary Gaussian noise, while actual measurement data frequently exhibit clear departures from these assumptions. Deriving methods from models more closely reflecting the data’s properties promises to yield more sensitive procedures. The commonly used matched filter is such a detection method that may be derived via a Gaussian model. In this paper we propose a generalized matched-filtering technique based on a Student-$t$ distribution that is able to account for heavier-tailed noise and is robust against outliers in the data. On the technical side, it generalizes the matched filter’s least-squares method to an iterative, or adaptive, variation. In a simplified Monte Carlo study we show that when applied to simulated signals buried in actual interferometer noise it leads to a higher detection rate than the usual (“Gaussian”) matched filter.

Cold dark matter in the Milky Way halo may have structure defined by flows with low velocity dispersion. The Axion Dark Matter eXperiment high resolution channel is especially sensitive to axions in such low velocity dispersion flows. Results from a combined power spectra analysis of the high resolution channel axion search are presented along with a discussion of the assumptions underlying such an analysis. We exclude Kim-Shifman-Vainshtein-Zakharov axion dark matter densities of $\rho \gtrsim 0.2\mathrm{GeV}/{\mathrm{cm}}^3$ and Dine-Fischler-Srednicki-Zhitnitskii densities of $\rho \gtrsim 1.4\mathrm{GeV}/{\mathrm{cm}}^3$ over a mass range of $m_a=3.3\mu \mathrm{eV}$ to $3.69\mu \mathrm{eV}$ for models having velocity dispersions of $\Delta \beta \lesssim 3\times {10}^{-6}$.

Spontaneous $CP$-violating phases that do not depend on the parameters of the Higgs sector—the so-called calculable phases—are investigated. The simplest realization is in models with 3 Higgs doublets, in which the scalar potential is invariant under non-Abelian symmetries. The non-Abelian discrete group $\mathsf{\Delta }(\mathsf{5}\mathsf{4})$ is shown to lead to the known structure of calculable phases obtained with $\mathsf{\Delta }(\mathsf{2}\mathsf{7})$. We investigate the possibility of accommodating the observed fermion masses and mixings.

LHC searches for the standard model Higgs Boson in $\gamma \gamma$ or $\tau \tau$ decay modes place strong constraints on the light technipion state predicted in technicolor models that include colored technifermions. Compared with the standard Higgs Boson, the technipions have an enhanced production rate (largely because the technipion decay constant is smaller than the weak scale) and also enhanced branching ratios into di-photon and di-tau final states (largely due to the suppression of $WW$ decays of the technipions). These factors combine to make the technipions more visible in both channels than a standard model Higgs would be. Hence, the recent ATLAS and CMS searches for Higgs bosons exclude the presence of technipions with masses from 110 GeV to nearly $2m_t$ in technicolor models that (a) include colored technifermions (b) feature topcolor dynamics and (c) have technicolor groups with three or more technicolors ($N_{\mathrm{TC}}\ge 3$). For certain models, the limits also apply out to higher technipion masses or down to the minimum number of technicolors ($N_{\mathrm{TC}}=2$). The limits may be softened somewhat in models where extended technicolor plays a significant role in producing the top quark’s mass. Additional LHC data on di-tau and di-photon final states will be extremely valuable in further exploring technicolor parameter space.

We predict an unconventional background free signal of the Higgs boson in $R$-parity violating nonminimal supersymmetric models at the Large Hadron Collider (LHC). The signal comprises a dilepton plus four hadronic jets and two large displaced vertices. The displaced leptons and jets are coming from the decay of the lightest supersymmetric particle (LSP), which is predominantly a gauge-singlet neutrino. A pair of such LSPs can couple to a Higgs boson, created via gluon fusion. We have analyzed two cases–one corresponding to the tree-level Higgs boson mass and another with the one-loop corrected mass of the Higgs boson. A reliable Higgs mass reconstruction using this signal can lead to discovery at the LHC with center-of-mass energy $\sqrt{s}=14\mathrm{TeV}$ and $5{\mathrm{fb}}^{-1}$ of integrated luminosity $(\mathcal{L})$. Even at $\sqrt{s}=7\mathrm{TeV}$ and $\mathcal{L}=5{\mathrm{fb}}^{-1}$, a reasonable number of events are expected. Besides, mass reconstruction of a gauge-singlet LSP can provide an estimate of the seesaw scale.

We explore an alternative mechanism for the production of gravitino dark matter whereby relic gravitinos originate from the decays of superpartners which are still in thermal equilibrium, i.e. via freeze-in. Contributions to the gravitino abundance from freeze-in can easily dominate over those from thermal scattering over a broad range of parameter space, e.g., when the scalar superpartners are heavy. Because the relic abundance from freeze-in is independent of the reheating temperature after inflation, collider measurements may be used to unambiguously reconstruct the freeze-in origin of gravitinos. In particular, if gravitino freeze-in indeed accounts for the present day dark matter abundance, then the lifetime of the next-to-lightest superpartner is uniquely fixed by the superpartner spectrum.

A model-independent search for direct $CP$ violation in the Cabibbo-suppressed decay $D^{+}\to K^{-}{K}^{+}{\pi }^{+}$ in a sample of approximately 370 000 decays is carried out. The data were collected by the LHCb experiment in 2010 and correspond to an integrated luminosity of $35{\mathrm{pb}}^{-1}$. The normalized Dalitz plot distributions for $D^{+}$ and $D^{-}$ are compared using four different binning schemes that are sensitive to different manifestations of $CP$ violation. No evidence for $CP$ asymmetry is found.

Earlier Kostelecky et al. [A. Kostelecky, N. Russell, and J. Tasson, Phys Rev Lett 100, 111102 (2008).] have obtained torsion bounds from Lorentz violation, where torsion components are taken from the axial part of torsion. In this brief report it is shown that more stringent bounds may be obtained by using nearly minimal magnetogenesis torsion trace instead of the minimal coupling between photons and axial torsion used by Kostelecky and his group. Just for comparison, in Kostelecky et al., the most stringent limit is estimated to be ${10}^{-31}\mathrm{GeV}$ while here one obtains ${10}^{-33}\mathrm{GeV}$. This estimate is obtained by constraining the torsion to galactic astronomy data. From the point of view of magnetogenesis, an interesting physical consequence is that dynamo action is obtained when the torsion trace background is negative, while the magnetic field energy decays when torsion is positive. Polarization of radio-galaxies can be used to obtain an even more stringent limit of $T\sim 1.7\times {10}^{-46}\mathrm{GeV}$ to Lorentz violation. Using WMAP, Kostelecky and Mewes [A. Kostelecky and M. Mewes, Astrophys. J. 689, L1 (2008)] have found limits of the order of ${10}^{-43}\mathrm{GeV}$. These results are obtained by making use of flat torsion modes [L. Garcia de Andrade, Phys Lett B 696, 1 (2011)], but may easily be extended to Riemann-Cartan spacetime.

A generalization of the Gell-Mann-Oaks-Renner relation to the case of infrared-conformal gauge theories is discussed. The starting point is the chiral Ward identity connecting the isovector pseudoscalar susceptibility to the chiral condensate, in a mass-deformed theory. A renormalization-group analysis shows that the pseudoscalar susceptibility is not saturated by the lightest state, but a contribution from the continuum part of the spectrum survives in the chiral limit. The computation also shows how infrared-conformal gauge theories behave differently, depending on whether the anomalous dimension of the chiral condensate be smaller or larger than 1. An application to lattice simulations is briefly discussed.

We develop an analytic formalism that allows one to quantify the stability properties of $\mathsf{X}$-type and $\mathsf{Y}$-type junctions in domain wall networks in two dimensions. A similar approach might be applicable to more general defect systems involving junctions that appear in a range of physical situations, for example, in the context of F- and D-type strings in string theory. We apply this formalism to a particular field theory, Carter’s pentavac model, where the strength of the symmetry breaking is governed by the parameter $|ϵ|<1$. We find that for low values of the symmetry breaking parameter $\mathsf{X}$-type junctions will be stable, whereas for higher values an $\mathsf{X}$-type junction will separate into two $\mathsf{Y}$-type junctions. The critical angle separating the two regimes is given by ${\alpha }_{\mathrm{c}}=293°\sqrt{|ϵ|}$ and this is confirmed using simple numerical experiments. We go on to simulate the pentavac model from random initial conditions, and we find that the fraction of $\mathsf{X}$-type junctions to $\mathsf{Y}$-type junctions is higher for smaller $ϵ$, although $\mathsf{X}$-type junctions do not appear to survive to late time. We also find that for small $ϵ$ the evolution of the number of domain walls $N_{\mathrm{dw}}$ in Minkowski space does not follow the standard $\propto t^{-1}$ scaling law with the deviation from the standard lore being more pronounced as $ϵ$ is decreased. The presence of dissipation appears to restore the $t^{-1}$ lore.

We calculate the evolution of the geometric entanglement entropy following a local quench in the D1-D5 conformal field theory, a two-dimensional theory that describes a particular bound state of D1 and D5 branes. The quench corresponds to a localized insertion of the exactly marginal operator that deforms the field theory off of the orbifold (free) point in its moduli space. This deformation ultimately leads to thermalization of the system. We find an exact analytic expression for the entanglement entropy of any spatial interval as a function of time after the quench and analyze its properties. This process is holographically dual to one stage in the formation of a stringy black hole.

We calibrate an effective-one-body (EOB) model to numerical-relativity simulations of mass ratios 1, 2, 3, 4, and 6, by maximizing phase and amplitude agreement of the leading (2, 2) mode and of the subleading modes (2, 1), (3, 3), (4, 4) and (5, 5). Aligning the calibrated EOB waveforms and the numerical waveforms at low frequency, the phase difference of the (2, 2) mode between model and numerical simulation remains below $\sim 0.1$ rad throughout the evolution for all mass ratios considered. The fractional amplitude difference at peak amplitude of the (2, 2) mode is 2% and grows to 12% during the ringdown. Using the Advanced LIGO noise curve we study the effectualness and measurement accuracy of the EOB model, and stress the relevance of modeling the higher-order modes for parameter estimation. We find that the effectualness, measured by the mismatch between the EOB and numerical-relativity polarizations which include only the (2, 2) mode, is smaller than 0.2% for binaries with total mass $20–200M_{\odot }$ and mass ratios 1, 2, 3, 4, and 6. When numerical-relativity polarizations contain the strongest seven modes, and stellar-mass black holes with masses less than $50M_{\odot }$ are considered, the mismatch for mass ratio 6 (1) can be as high as 7% (0.2%) when only the EOB (2, 2) mode is included, and an upper bound of the mismatch is 0.5% (0.07%) when all the four subleading EOB modes calibrated in this paper are taken into account. For binaries with intermediate-mass black holes with masses greater than $50M_{\odot }$ the mismatches are larger. We also determine for which signal-to-noise ratios the EOB model developed here can be used to measure binary parameters with systematic biases smaller than statistical errors due to detector noise.

Colored tensor models generalize matrix models in arbitrary dimensions, yielding a statistical theory of random higher-dimensional topological spaces. They admit a $1/N$ expansion dominated by graphs of spherical topology. The simplest tensor model one can consider maps onto a rectangular matrix model with skewed scalings. We analyze this simplest toy model and show that it exhibits a family of multicritical points and a novel double scaling limit. We show in $D=3$ dimensions that only graphs representing spheres contribute in the double scaling limit and argue that similar results hold for any dimension.

In double field theory, the equation of motion for a point particle in the background field is considered. We find that the motion is described by a geodesic flow in the doubled geometry. Inspired by the analysis on the particle motion, we consider a modified model of quantum string cosmology, which includes two scale factors.