The dwarf spheroidal satellite galaxies of the Milky Way are some of the most dark-matter-dominated objects known. Due to their proximity, high dark matter content, and lack of astrophysical backgrounds, dwarf spheroidal galaxies are widely considered to be among the most promising targets for the indirect detection of dark matter via $\gamma$ rays. Here we report on $\gamma$-ray observations of 25 Milky Way dwarf spheroidal satellite galaxies based on 4 years of Fermi Large Area Telescope (LAT) data. None of the dwarf galaxies are significantly detected in $\gamma$ rays, and we present $\gamma$-ray flux upper limits between 500 MeV and 500 GeV. We determine the dark matter content of 18 dwarf spheroidal galaxies from stellar kinematic data and combine LAT observations of 15 dwarf galaxies to constrain the dark matter annihilation cross section. We set some of the tightest constraints to date on the annihilation of dark matter particles with masses between 2 GeV and 10 TeV into prototypical standard model channels. We find these results to be robust against systematic uncertainties in the LAT instrument performance, diffuse $\gamma$-ray background modeling, and assumed dark matter density profile.

A combined search for the Standard Model Higgs boson with the ATLAS detector at the LHC is presented. The data sets used correspond to integrated luminosities from $4.6{\mathrm{fb}}^{-1}$ to $4.9{\mathrm{fb}}^{-1}$ of proton-proton collisions collected at $\sqrt{s}=7\mathrm{TeV}$ in 2011. The Higgs boson mass ranges of 111.4 GeV to 116.6 GeV, 119.4 GeV to 122.1 GeV, and 129.2 GeV to 541 GeV are excluded at the 95% confidence level, while the range 120 GeV to 560 GeV is expected to be excluded in the absence of a signal. An excess of events is observed at Higgs boson mass hypotheses around 126 GeV with a local significance of 2.9 standard deviations ($\sigma$). The global probability for the background to produce an excess at least as significant anywhere in the entire explored Higgs boson mass range of 110–600 GeV is estimated to be $\sim 15\%$, corresponding to a significance of approximately $1\sigma$.

We evaluate the partition function of three-dimensional theories of gravity in the quantum regime, where the anti–de Sitter (AdS) radius is Planck scale and the central charge is of order one. The contribution from the AdS vacuum sector can—with certain assumptions—be computed and equals the vacuum character of a minimal model conformal field theory. The torus partition function is given by a sum over geometries which is finite and computable. For generic values of Newton’s constant $G$ and the AdS radius $\ell$, the result has no Hilbert space interpretation, but in certain cases it agrees with the partition function of a known conformal field theory. For example, the partition function of pure Einstein gravity with $G=3\ell$ equals that of the Ising model, providing evidence that these theories are dual. We also present somewhat weaker evidence that the three-state and tricritical Potts models are dual to pure higher spin theories of gravity based on $SL(3)$ and $E_6$, respectively.

We show that bound states moving in a finite periodic volume have an energy correction which is topological in origin and universal in character. The topological volume corrections contain information about the number and mass of the constituents of the bound states. These results have broad applications to lattice calculations involving nucleons, nuclei, hadronic molecules, and cold atoms. We illustrate and verify the analytical results with several numerical lattice calculations.

Collinear and soft divergences in perturbative quantum gravity are investigated to arbitrary orders in amplitudes for wide-angle scattering, using methods developed for gauge theories. We show that collinear singularities cancel when all such divergent diagrams are summed over, by using the gravitational Ward identity that decouples unphysical polarizations from the S-matrix. This analysis generalizes a result previously demonstrated in the eikonal approximation. We also confirm that the only virtual graviton corrections that give soft logarithmic divergences are of the ladder and crossed ladder types.

The scattering of two Dashen-Hasslacher-Neveu baryons in the large $N$ Gross-Neveu model is solved exactly using the relativistic, time-dependent Hartree-Fock approach. Unlike the special case of kink-antikink scattering, the scattering of Dashen-Hasslacher-Neveu baryons is sensitive to the backreaction of the fermions bound inside the baryons. Correspondingly the solution is much more complicated than the kink-antikink scattering solutions, which can be expressed in terms of sinh-Gordon solitons. Nevertheless, we present a simple ansatz form that gives closed analytic expressions for both the space–time-dependent mean fields and the Dirac spinors for all continuum and bound states. The solution can also be applied to the scattering of polarons and solitons in conducting polymers.

In the picture of eternal inflation, our observable universe resides inside a single bubble nucleated from an inflating false vacuum. Many of the theories giving rise to eternal inflation predict that we have causal access to collisions with other bubble universes, providing an opportunity to confront these theories with observation. We present the results from the first observational search for the effects of bubble collisions, using cosmic microwave background data from the WMAP satellite. Our search targets a generic set of properties associated with a bubble-collision spacetime, which we describe in detail. We use a modular algorithm that is designed to avoid a posteriori selection effects, automatically picking out the most promising signals, performing a search for causal boundaries, and conducting a full Bayesian parameter estimation and model selection analysis. We outline each component of this algorithm, describing its response to simulated CMB skies with and without bubble collisions. Comparing the results for simulated bubble collisions to the results from an analysis of the WMAP 7-year data, we rule out bubble collisions over a range of parameter space. Our model selection results based on WMAP 7-year data do not warrant augmenting $\Lambda \mathrm{CDM}$ with bubble collisions. Data from the Planck satellite can be used to more definitively test the bubble-collision hypothesis.

The rare $K\to \pi \nu \overline{\nu }$ decays play a central role in testing the standard model and its extensions. Upcoming experiments plan to measure the decay rates with high accuracy. Yet, unknown higher-order electroweak corrections result in a sizeable theory error. We remove this uncertainty by computing the full two-loop electroweak corrections to the top-quark contribution $X_t$ to the rare decays $K_L\to {\pi }^0\nu \overline{\nu }$, $K^{+}\to {\pi }^{+}\nu \overline{\nu }$, and $B\to X_{d,s}\nu \overline{\nu }$ in the standard model. The remaining theoretical uncertainty related to electroweak effects is now far below 1%. Finally we update the branching ratios to find $\mathrm{Br}(K_L\to {\pi }^0\nu \overline{\nu })=2.43(39)(6)\times {10}^{-11}$ and $\mathrm{Br}(K^{+}\to {\pi }^{+}\nu \overline{\nu })=7.81(75)(29)\times {10}^{-11}$. The first error summarizes the parametric, the second the remaining theoretical uncertainties.

We present the complete four-loop four-point amplitude in $\mathcal{N}=4$ super-Yang-Mills theory, for a general gauge group and general $D$-dimensional covariant kinematics, and including all nonplanar contributions. We use the method of maximal cuts—an efficient application of the unitarity method—to construct the result in terms of 50 four-loop integrals. We give graphical rules, valid in $D$ dimensions, for obtaining various nonplanar contributions from previously-determined terms. We examine the ultraviolet behavior of the amplitude near $D=11/2$. The nonplanar terms are as well-behaved in the ultraviolet as the planar terms. However, in the color decomposition of the three- and four-loop amplitude for an $SU(N_c)$ gauge group, the coefficients of the double-trace terms are better behaved in the ultraviolet than are the single-trace terms. The results from this paper were an important step toward obtaining the corresponding amplitude in $\mathcal{N}=8$ supergravity, which confirmed the existence of cancellations beyond those needed for ultraviolet finiteness at four loops in four dimensions. Evaluation of the loop integrals near $D=4$ would permit tests of recent conjectures and results concerning the infrared behavior of four-dimensional massless gauge theory.

We measure the charge asymmetry $A$ of like-sign dimuon events in $6.1{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions recorded with the D0 detector at a center-of-mass energy $\sqrt{s}=1.96\mathrm{TeV}$ at the Fermilab Tevatron collider. From $A$, we extract the like-sign dimuon charge asymmetry in semileptonic $b$-hadron decays: $A_{\mathrm{sl}}^b=-0.00957\pm 0.00251(\mathrm{stat})\pm 0.00146(\mathrm{syst})$. This result differs by 3.2 standard deviations from the standard model prediction $A_{\mathrm{sl}}^b(\mathrm{SM})=(-{2.3}_{-0.6}^{+0.5})\times {10}^{-4}$ and provides first evidence of anomalous $CP$ violation in the mixing of neutral $B$ mesons.

Using gauge/gravity duality, we compute the energy density and angular distribution of the power radiated by a quark undergoing circular motion in strongly coupled $\mathcal{N}=4$ supersymmetric Yang-Mills theory. We compare the strong coupling results to those at weak coupling, finding them to be very similar. In both regimes, the angular distribution of the radiated power is in fact similar to that of synchrotron radiation produced by an electron in circular motion in classical electrodynamics: the quark emits radiation in a narrow beam along its velocity vector with a characteristic opening angle $\alpha \sim 1/\gamma$. To an observer far away from the quark, the emitted radiation appears as a short periodic burst, just like the light from a lighthouse does to a ship at sea. Our strong coupling results are valid for any strongly coupled conformal field theory with a dual classical gravity description.

We perform an $\mathcal{O}({\alpha }_s^2)$ perturbative calculation of the equation of state of cold but dense QCD matter with two massless and one massive quark flavor, finding that perturbation theory converges reasonably well for quark chemical potentials above 1 GeV. Using a running coupling constant and strange quark mass, and allowing for further nonperturbative effects, our results point to a narrow range where absolutely stable strange quark matter may exist. Absent stable strange quark matter, our findings suggest that quark matter in (slowly rotating) compact star cores becomes confined to hadrons only slightly above the density of atomic nuclei. Finally, we show that equations of state including quark matter lead to hybrid star masses up to $M\sim 2M_{\odot }$, in agreement with current observations. For strange stars, we find maximal masses of $M\sim 2.75M_{\odot }$ and conclude that confirmed observations of compact stars with $M>2M_{\odot }$ would strongly favor the existence of stable strange quark matter.

We show that the linearization of all exact solutions of classical chiral gravity around the ${\mathrm{AdS}}_3$ vacuum have positive energy. Nonchiral and negative-energy solutions of the linearized equations are infrared divergent at second order, and so are removed from the spectrum. In other words, chirality is confined and the equations of motion have linearization instabilities. We prove that the only stationary, axially symmetric solutions of chiral gravity are BTZ black holes, which have positive energy. It is further shown that classical log gravity—the theory with logarithmically relaxed boundary conditions—has finite asymptotic symmetry generators but is not chiral and hence may be dual at the quantum level to a logarithmic conformal field theories (CFT). Moreover we show that log gravity contains chiral gravity within it as a decoupled charge superselection sector. We formally evaluate the Euclidean sum over geometries of chiral gravity and show that it gives precisely the holomorphic extremal CFT partition function. The modular invariance and integrality of the expansion coefficients of this partition function are consistent with the existence of an exact quantum theory of chiral gravity. We argue that the problem of quantizing chiral gravity is the holographic dual of the problem of constructing an extremal CFT, while quantizing log gravity is dual to the problem of constructing a logarithmic extremal CFT.

Quantum gravity in the region very near the horizon of an extreme Kerr black hole (whose angular momentum and mass are related by $J=G{M}^2$) is considered. It is shown that consistent boundary conditions exist, for which the asymptotic symmetry generators form one copy of the Virasoro algebra with central charge $c_L=\frac{12J}{\hslash }$. This implies that the near-horizon quantum states can be identified with those of (a chiral half of) a two-dimensional conformal field theory (CFT). Moreover, in the extreme limit, the Frolov-Thorne vacuum state reduces to a thermal density matrix with dimensionless temperature $T_L=\frac{1}{2\pi }$ and conjugate energy given by the zero mode generator, $L_0$, of the Virasoro algebra. Assuming unitarity, the Cardy formula then gives a microscopic entropy $S_{\mathrm{micro}}=\frac{2\pi J}{\hslash }$ for the CFT, which reproduces the macroscopic Bekenstein-Hawking entropy $S_{\mathrm{macro}}=\frac{\mathrm{Area}}{4\hslash G}$. The results apply to any consistent unitary quantum theory of gravity with a Kerr solution. We accordingly conjecture that extreme Kerr black holes are holographically dual to a chiral two-dimensional conformal field theory with central charge $c_L=\frac{12J}{\hslash }$, and, in particular, that the near-extreme black hole GRS 1915+105 is approximately dual to a CFT with $c_L\sim 2\times {10}^{79}$.

We present atom-interferometer tests of the local Lorentz invariance of post-Newtonian gravity. An experiment probing for anomalous vertical gravity on Earth, which has already been performed, uses the highest-resolution atomic gravimeter so far. The influence of Lorentz violation in electrodynamics is also taken into account, resulting in combined bounds on Lorentz violation in gravity and electrodynamics. Expressed within the standard model extension or Nordtvedt’s anisotropic universe model, we limit 12 linear combinations of seven coefficients for Lorentz violation at the part per billion level, from which we derive limits on six coefficients (and seven when taking into account additional data from lunar laser ranging). We also discuss the use of horizontal interferometers, including atom-chip or guided-atom devices, which potentially allow the use of longer coherence times in order to achieve higher sensitivity.

Traditional ideas for testing unification involve searching for the decay of the proton and its branching modes. We point out that several astrophysical experiments are now reaching sensitivities that allow them to explore supersymmetric unified theories. In these theories the electroweak-mass dark matter particle can decay, just like the proton, through dimension 6 operators with lifetime $\sim {10}^{26}\mathrm{s}$. Interestingly, this time scale is now being investigated in several experiments including ATIC, PAMELA, HESS, and Fermi. Positive evidence for such decays may be opening our first direct window to physics at the supersymmetric unification scale of $M_{\mathrm{GUT}}\sim {10}^{16}\mathrm{GeV}$, as well as the TeV scale. Moreover, in the same supersymmetric unified theories, dimension 5 operators can lead a weak-scale superparticle to decay with a lifetime of $\sim 100\mathrm{s}$. Such decays are recorded by a change in the primordial light element abundances and may well explain the present discord between the measured Li abundances and standard big bang nucleosynthesis, opening another window to unification. These theories make concrete predictions for the spectrum and signatures at the LHC as well as Fermi.

We present a candidate quantum field theory of gravity with dynamical critical exponent equal to $z=3$ in the UV. (As in condensed-matter systems, $z$ measures the degree of anisotropy between space and time.) This theory, which at short distances describes interacting nonrelativistic gravitons, is power-counting renormalizable in $3+1$ dimensions. When restricted to satisfy the condition of detailed balance, this theory is intimately related to topologically massive gravity in three dimensions, and the geometry of the Cotton tensor. At long distances, this theory flows naturally to the relativistic value $z=1$, and could therefore serve as a possible candidate for a UV completion of Einstein’s general relativity or an infrared modification thereof. The effective speed of light, the Newton constant and the cosmological constant all emerge from relevant deformations of the deeply nonrelativistic $z=3$ theory at short distances.