Dark matter annihilation is proportional to the square of the density and is especially efficient in places of highest concentration of dark matter, such as dark matter spikes. The spikes are formed as a result of contraction of the dark matter density profile caused by adiabatic growth of a supermassive black hole at the center of the dark matter halo or subhalo. We revisit the relation between the properties and mass functions of dark matter halos and spikes and propose alternative models for the density spikes that can potentially contribute to the isotropic gamma ray background.

The existence of neutron stars with masses of $\sim 2M_{\odot }$ requires a stiff equation of state at high densities. On the other hand, the necessary appearance also at high densities of new degrees of freedom, such as hyperons and $\mathrm{\Delta }$ resonances, can lead to a strong softening of the equation of state with resulting maximum masses of $\sim 1.5M_{\odot }$ and radii smaller than $\sim 10\mathrm{km}$. Hints for the existence of compact stellar objects with very small radii have been found in recent statistical analyses of quiescent low-mass X-ray binaries in globular clusters. We propose an interpretation of these two apparently contradicting measurements, large masses and small radii, in terms of two separate families of compact stars: hadronic stars, whose equation of state is soft, can be very compact, while quark stars, whose equation of state is stiff, can be very massive. In this respect an early appearance of $\mathrm{\Delta }$ resonances is crucial to guarantee the stability of the branch of hadronic stars. Our proposal could be tested by measurements of radii with an error of $\sim 1\mathrm{km}$, which is within reach of the planned Large Observatory for X-ray Timing satellite, and it would be further strengthened by the discovery of compact stars heavier than $\sim 2M_{\odot }$.

The integration time required by space experiments to perform high accuracy tests of the universality of free fall and the weak equivalence principle is a crucial issue. It is inversely proportional to the square of the acceleration to be measured, which is extremely small; the duration of the mission is a severe limitation and experiments in space lack repeatability. An exceedingly long integration time can therefore rule out a mission target. We have evaluated the integration time due to thermal noise from gas damping, Johnson noise and eddy currents—which are independent of the signal frequency—and to internal damping, which is known to decrease with increasing frequency. It is found that at low frequencies thermal noise from internal damping dominates. In the “Galileo Galilei” proposed space experiment to test the equivalence principle to ${10}^{-17}$ the rapid rotation of the satellite (1 Hz) up-converts the signal to a frequency region where thermal noise from internal damping is lower than gas damping and only a factor 2 higher than Johnson noise, with a total integration time of 2.4 to 3.5 hours even in a very conservative estimate. With an adequate readout and additional care in reducing systematics the test could be improved by another order of magnitude, close to ${10}^{-18}$, requiring a hundred times longer—still affordable—integration time of 10 to 14.6 days. $\mu \text{SCOPE}$, a similar room temperature mission under construction by the French space agency to be launched in 2015, aims at a ${10}^{-15}$ test with an estimated integration time of 1.4 days. Space tests using cold atoms and atom interferometry have been proposed to be performed on the space station (Q-WEP, to ${10}^{-14}$) and on a dedicated mission (STE-QUEST, to ${10}^{-15}$ like $\mu \text{SCOPE}$). In this case integration is required in order to reduce single shot noise. European Space Agency funded studies report an integration time of several months and a few years respectively.

The Peccei-Quinn anomalous global $U{(1)}_{PQ}$ symmetry is important for solving the strong $CP$ problem with a cosmologically relevant axion. We add to this the simple (but hitherto unexplored) observation that it also has a residual $Z_2$ symmetry which may be responsible for a second component of dark matter, i.e., an absolutely stable weakly interacting singlet scalar. This new insight provides a theoretical justification for this simplest of all possible dark-matter models. It also connects with the notion of generating radiative neutrino mass through dark matter. Two such specific realizations are proposed. In our general scenario, dark-matter detection is guaranteed at existing direct-detection experiments and/or axion searches. Observable signals at the Large Hadron Collider are discussed.

In a large variety of quantum mechanical systems, we show that the full nonperturbative expression for energy eigenvalues, containing all orders of perturbative, nonperturbative, and quasi-zero-mode terms, may be generated directly from the perturbative expansion about the perturbative vacuum, combined with a single global boundary condition. This provides a dramatic realization of the principle of “resurgence,” that the fluctuations about different semiclassical saddle points are related to one another in a precise quantitative manner. The analysis of quantum mechanics also generalizes to certain calculable regimes of quantum field theory.

Existing models of dynamical electroweak symmetry breaking (EWSB) find it very difficult to get a Higgs of mass lighter than $m_t$. Consequently, in light of the LHC discovery of the $\sim 125\mathrm{GeV}$ Higgs, such models face a significant obstacle. Moreover, with three generations those models have a superheavy cutoff around $10^{17}\mathrm{GeV}$, requiring a significant fine-tuning. To overcome these twin difficulties, we propose a hybrid framework for EWSB, in which the Higgs mechanism is combined with a Nambu-Jona-Lasinio mechanism. The model introduces a strongly coupled doublet of heavy quarks with a mass around 500 GeV, which forms a condensate at a compositeness scale $\mathrm{\Lambda }$ about a few TeV, and an additional unconstrained scalar doublet which behaves as a “fundamental” doublet at $\mathrm{\Lambda }$. This “fundamental”-like doublet has a vanishing quartic term at $\mathrm{\Lambda }$ and is, therefore, not the SM doublet, but should rather be viewed as a pseudo-Goldstone boson of the underlying strong dynamics. This setup is matched at the compositeness scale $\mathrm{\Lambda }$ to a tightly constrained hybrid two Higgs doublet model, where both the composite and unconstrained scalars participate in EWSB. This allows us to get a good candidate for the recently observed 125 GeV scalar which has properties very similar to the Standard Model Higgs. The heavier (mostly composite) $CP$-even scalar has a mass around 500 GeV, while the pseudoscalar and the charged Higgs particles have masses in the range 200–300 GeV.

We evaluate the three-loop corrections to the matching coefficient of the vector current between quantum chromodynamics (QCD) and nonrelativistic QCD. The result is presented in the $\overline{\mathrm{MS}}$ scheme where large perturbative corrections are observed. The implications on the threshold production of top-quark pairs are briefly discussed.

We present the first results of a new global next-to-leading order analysis of spin-dependent parton distribution functions from the most recent world data on inclusive polarized deep-inelastic scattering, focusing in particular on the large-$x$ and low-$Q^2$ regions. By directly fitting polarization asymmetries we eliminate biases introduced by using polarized structure function data extracted under nonuniform assumptions for the unpolarized structure functions. For analysis of the large-$x$ data we implement nuclear smearing corrections for deuterium and ${}^3\mathrm{He}$ nuclei, and systematically include target mass and higher twist corrections to the $g_1$ and $g_2$ structure functions at low $Q^2$. We also explore the effects of $Q^2$ and $W^2$ cuts in the data sets, and the potential impact of future data on the behavior of the spin-dependent parton distributions at intermediate and large $x$.

Higgs pair production is crucial for measuring the Higgs boson self-coupling. The dominant channel at hadron colliders is gluon fusion via heavy-quark loops. We present the results of a fully exclusive simulation of gluon fusion Higgs pair production based on the matrix elements for $hh+0$, 1 partons including full heavy-quark loop dependence, matched to a parton shower. We examine and validate this new description by comparing it with (a) Higgs effective theory predictions, (b) exact $hh+0$-parton sample showered by Pythia, and (c) exact $hh+1$-parton distributions, by looking at the most relevant kinematic distributions, such as $p_T^h$, $p_T^{hh}$, $M_{hh}$ spectra, and the jet rate as well. We find that matched samples provide a state-of-the-art accurate exclusive description of the final state.

We show that current Higgs data permit a significantly enhanced Higgs coupling to charm pairs, comparable to the Higgs-to-bottom pairs coupling in the Standard Model, without resorting to additional new physics sources in Higgs production. With a mild level of the latter current data even allow for the Higgs-to-charm pairs to be the dominant decay channel. An immediate consequence of such a large charm coupling is a significant reduction of the Higgs signal strengths into the known final states as in particular into bottom pairs. This might reduce the visible vector-boson associated Higgs production rate to a level that could compromise the prospects of ever observing it. We however demonstrate that a significant fraction of this reduced signal can be recovered by jet-flavor tagging targeted towards charm-flavored jets. Finally we argue that an enhanced Higgs-to-charm pairs coupling can be obtained in various new physics scenarios in the presence of only a mild accidental cancellation between various contributions.

A precise comparison is made between the Dalitz decay $H\to \ell \overline{\ell }\gamma$ and the two-body decay $H\to \gamma Z$, $Z\to \ell \overline{\ell }$ for electrons and for muons including experimental cuts appropriate for the ATLAS detector. The widths for these two processes differ by 8% for electrons and 3% for muons. Given that there remain uncertainties of this order that are not included, this suggests that the isolation of the Dalitz decay will be challenging.

The recent observation of two PeV events at IceCube, followed by an additional 26 events between 30 and 300 TeV, has generated considerable speculations on its origin, and many exotic new physics explanations have been invoked. For a reliable interpretation, it is, however, important to first scrutinize the Standard Model (SM) expectations carefully, including the theoretical uncertainties, mainly due to the parton distribution functions. Assuming a new isotropic cosmic neutrino flux with a simple unbroken power-law spectrum, $\mathrm{\Phi }\propto E^{-s}$ for the entire energy range of interest, we find that with $s=1.5–2$, the SM neutrino-nucleon interactions are sufficient to explain all the observed events so far, without the need for any beyond the SM explanation. With more statistics, this powerful detector could provide a unique test of the SM up to the PeV scale and lead to important clues of new physics.

It is demonstrated, owing to the nonlinearity of QED, that a static charge placed in a strong magnetic field $B$ is a magnetic dipole (besides remaining an electric monopole, as well). Its magnetic moment grows linearly with $B$ as long as the latter remains smaller than the characteristic value of $1.2\times {10}^{13}\mathrm{G}$ but tends to a constant as $B$ exceeds that value. The force acting on a densely charged object by the dipole magnetic field of a neutron star is estimated.

General-relativistic stable spacetimes can be made unstable under the presence of certain nonminimally coupled free scalar fields. In this paper, we analyze the evolution of linear scalar-field perturbations in spherically symmetric spacetimes and compare the classical stability analysis with a recently discussed quantum field one. In particular, it is shown that vacuum fluctuations lead to natural seeds for the unstable phase, whereas in the classical framework the presence of such seeds in the initial conditions must be assumed.

Using the coset approach (nonlinear realization) we construct component actions for a superparticle in three-dimensional spacetime with $\mathcal{N}=4$ supersymmetry partially broken to $\mathcal{N}=2$. These actions may contain an anyonic term and the square of the first extrinsic worldline curvature. We present the supercharges for the unbroken and broken supersymmetries as well as the Hamiltonian for the supersymmetric anyon. In terms of the nonlinear realization superfields, the superspace actions take a simple form in all cases.

We construct a theory of particles moving in both curved momentum space and spacetime, being a generalization of relative locality. We find that in order to construct such a theory, with desired symmetries, including the general coordinate invariance, we have to use nonlocal position variables. It turns out that free particles move on geodesics and momentum dependent translations of relative locality are replaced with momentum dependent geodesic deviations.

The black hole final state proposal reconciles the infalling vacuum with the unitarity of the Hawking radiation, but only for some experiments. We study experiments that first verify the exterior, then the interior purification of the same Hawking particle. (This is the same protocol that renders the firewall paradox operationally meaningful in standard quantum mechanics.) We show that the decoherence functional fails to be diagonal, even upon inclusion of external “pointer” systems. Hence, probabilities for outcomes of these measurements are not defined. We conclude that the final state proposal does not offer a consistent alternative to the firewall hypothesis.

In a perturbed universe, comoving tracers on a two-dimensional surface of constant observed redshift are at different proper times since the big bang. For tracers whose age is known independently, one can measure these perturbations of the proper time. Examples of such sources include cosmic events which only happen during a short period of cosmic history, as well as evolving standard candles and standard rulers. In this paper, we derive a general gauge-invariant linear expression for this perturbation in terms of spacetime perturbations. We show that this perturbation in general contributes a previously overlooked leading order term to observables such as the magnification (although this contribution is generally small). Further, as an illustrative example, we show that the observed temperature perturbations of the cosmic microwave background on large scales ($\ell \ll 100$) are exactly given by these proper-time perturbations. Together with the six ruler perturbations derived in [F. Schmidt and D. Jeong, Phys. Rev. D 86, 083527 (2012)], this completes the set of independent observables which can be measured with standard rulers and candles.

The rapid rise in the cosmic ray positron fraction above 10 GeV, as measured by PAMELA and AMS, suggests the existence of nearby primary sources of high energy positrons, such as pulsars or annihilating/decaying dark matter. In contrast, the spectrum of secondary positrons produced through the collisions of cosmic rays in the interstellar medium is predicted to fall rapidly with energy, and thus is unable to account for the observed rise. It has been proposed, however, that secondary positrons could be produced and then accelerated in nearby supernova remnants, potentially explaining the observed rise, without the need of primary positron sources. Yet, if secondary positrons are accelerated in such shocks, other secondary cosmic ray species (such as boron nuclei and antiprotons) will also be accelerated, leading to rises in the boron-to-carbon and antiproton-to-proton ratios. The measurements of the boron-to-carbon ratio by the PAMELA and AMS collaborations, however, show no sign of such a rise. With this new data in hand, we revisit the secondary acceleration scenario for the rising positron fraction. Assuming that the same supernova remnants accelerate both light nuclei (protons, helium) and heavier cosmic ray species, we find that no more than $\sim 25\%$ of the observed rise in the positron fraction can result from this mechanism (at the 95% confidence level).

Rotating and magnetized protoneutron stars may drive relativistic magnetocentrifugally accelerated winds as they cool immediately after core collapse. The wind fluid near the star is composed of neutrons and protons, and the neutrons become relativistic while collisionally coupled with the ions. Here, we argue that the neutrons in the flow eventually undergo inelastic collisions around the termination shock inside the stellar material, producing $\sim 0.1–1\mathrm{GeV}$ neutrinos, without relying on cosmic-ray acceleration mechanisms. Even higher-energy neutrinos may be produced via particle acceleration mechanisms. We show that Precision IceCube Next Generation Upgrade and Hyper-Kamiokande can detect such neutrinos from nearby core-collapse supernovae, by reducing the atmospheric neutrino background via coincident detection of MeV neutrinos or gravitational waves and optical observations. Detection of these GeV and/or higher-energy neutrinos would provide important clues to the physics of magnetic acceleration, nucleosynthesis, the relation between supernovae and gamma-ray bursts, and the properties of newly born neutron stars.