We discuss a mechanism for the apparently universal scaling in the high-multiplicity tail of charged particle distributions for high-energy nuclear collisions. We argue that this scaling behavior originates from rare fluctuations of the nucleon density. We discuss a pair of simple models of proton shape fluctuations. A “fat” proton with a size of 3 fm occurs with observable frequency. In light of this result, collective flow behavior in the ensuing nuclear interaction seems feasible. We discuss the influence of these models on the large-$x$ structure of the proton and the likely influences on the distribution of initial-state spatial eccentricities ${\epsilon }_n$.

We present a recipe that allows us to construct multicentered black holes embedded in an arbitrary Friedmann-Lemaître-Robertson-Walker (FLRW) universe. These solutions are completely determined by a function satisfying the conformal Laplace equation on the spatial slices ${\mathrm{E}}^3$, ${\mathrm{S}}^3$, or ${\mathrm{H}}^3$. Since anti–de Sitter (AdS) space can be written in FLRW coordinates, this includes as a special case multicentered black holes in AdS, in the sense that, far away from the black holes, the energy density and the pressure approach the values given by a negative cosmological constant. We study in some detail the physical properties of the single-centered asymptotically AdS case, which does not coincide with the usual Reissner-Nordström-AdS black hole, but is highly dynamical. In particular, we determine the curvature singularities and trapping horizons of this solution, compute the surface gravity of the trapping horizons, and show that the generalized first law of black hole dynamics proposed by Hayward holds in this case. It turns out that the spurious big bang/big crunch singularities that appear when one writes AdS in FLRW form become real in the presence of these dynamical black holes. This implies that actually only one point of the usual conformal boundary of AdS survives in the solutions that we construct. Finally, a generalization to arbitrary dimension is also presented.

We propose and develop a general algorithm for finding the action for cosmological perturbations which rivals the conventional, gauge-invariant approach and can be applied to theories with more than one metric. We then apply it to a particular case of bigravity, focusing on the Eddington-inspired Born-Infeld theory, and show that we can obtain a nearly scale-invariant power spectrum for both scalar and tensor primordial quantum perturbations. Unfortunately, in the case of the minimal Eddington-inspired Born-Infeld theory, we find that the tensor-to-scalar ratio of perturbations is unacceptably large. We discuss the applicability of our general method and the possibility of resurrecting the specific theory we have looked at.

We compute the tree-level scattering amplitude between two covariantly conserved sources in generic cosmological topologically massive gravity augmented with a Fierz-Pauli term that has three massive degrees of freedom. We consider the chiral gravity limit in the anti–de Sitter space as well as the limit of flat-space chiral gravity. We show that chiral gravity cannot be unitarily deformed with a Fierz-Pauli mass. We calculate the nonrelativistic potential energy between two point-like spinning sources. In addition to the expected mass-mass and spin-spin interactions, there are mass-spin interactions due to the presence of the gravitational Chern-Simons term which induces spin for any massive object and turns it to an anyon. We also show that the tree-level scattering is trivial for the flat-space chiral gravity.

The recent Planck data of cosmic microwave background temperature anisotropies support the Starobinsky theory in which the quadratic Ricci scalar drives cosmic inflation. We build up a multidimensional quantum consisted ultraviolet completion of the model in a phenomenological “bottom-up approach.” We present the maximal class of theories compatible with unitarity and (super-)renormalizability or finiteness which reduces to the Starobinsky theory in the low-energy limit. The outcome is a maximal extension of the Krasnikov-Tomboulis-Modesto theory including an extra scalar degree of freedom besides the graviton field. The original theory was afterwards independently discovered by Biswas-Gerwick-Koivisto-Mazumdar starting from first principles. We explicitly show power counting super-renormalizability or finiteness (in odd dimensions) and unitarity (no ghosts) of the theory. Any further extension of the theory is nonunitary, confirming the existence of at most one single extra degree of freedom, the scalaron. A mechanism to achieve the Starobinsky theory in string (field) theory is also investigated at the end of the paper.

As direct dark matter experiments continue to increase in size, they will become sensitive to neutrinos from astrophysical sources. For experiments that do not have directional sensitivity, coherent neutrino scattering from several sources represents an important background to understand, as it can almost perfectly mimic an authentic weakly interacting massive particle (WIMP) signal. Here we explore in detail the effect of neutrino backgrounds on the discovery potential of WIMPs over the entire mass range of 500 MeV to 10 TeV. We show that, given the theoretical and measured uncertainties on the neutrino backgrounds, direct detection experiments lose sensitivity to light ($\sim 10\mathrm{GeV}$) and heavy ($\sim 100\mathrm{GeV}$) WIMPs with a spin-independent cross section below ${10}^{-45}$ and ${\text{10}}^{-49}{\mathrm{cm}}^2$, respectively.

Within the minimal supersymmetric Standard Model (MSSM), LHC bounds suggest that scalar superpartner masses are far above the electroweak scale. Given a high superpartner mass, nonthermal dark matter is a viable alternative to WIMP dark matter generated via freezeout. In the presence of moduli fields, nonthermal dark matter production is associated with a long matter-dominated phase, modifying the spectral index and primordial tensor amplitude relative to those in a thermalized primordial universe. Nonthermal dark matter can have a higher self-interaction cross section than its thermal counterpart, enhancing astrophysical bounds on its annihilation signals. We constrain the contributions to the neutralino mass from the bino, wino and Higgsino using existing astrophysical bounds and direct detection experiments for models with nonthermal neutralino dark matter. Using these constraints we quantify the expected change to inflationary observables resulting from the nonthermal phase.

Relativistic scalar fields are ubiquitous in modified theories of gravity. An important tool in understanding their on structure formation, especially in the context of N-body simulations, is the quasistatic approximation in which the time evolution of perturbations in the scalar fields is discarded. We show that this approximation must be used with some care by studying linearly perturbed scalar field cosmologies and quantifying the errors that arise from taking the quasistatic limit. We focus on $f(R)$ and chameleon models and link the accuracy of the quasistatic approximation to the fast/slow-roll behavior of the background and its proximity to $\mathrm{\Lambda }\mathrm{CDM}$. Investigating a large range of scales, from super- to subhorizon, we find that slow-rolling ($\mathrm{\Lambda }\mathrm{CDM}$-like) backgrounds generically result in good quasistatic behavior, even on (super-)horizon scales. We also discuss how the approximation might affect studying the nonlinear growth of structure in numerical N-body simulations.

We derive constraints on elastic scattering between baryons and dark matter using the cosmic microwave background (CMB) data from the Planck satellite and the Lyman-$\alpha$ forest data from the Sloan Digital Sky Survey. Elastic scattering allows baryons and dark matter to exchange momentum, affecting the dynamics of linear density perturbations in the early universe. We derive constraints to scattering cross sections of the form $\sigma \propto v^n$, allowing for a wide range of velocity dependencies with $-4\le n\le 2$. We improve and correct previous estimates where they exist, including velocity-independent cross section as well as dark matter millicharge and electromagnetic dipole moments. Lyman-$\alpha$ forest data dominate the constraints for $n>-3$, where the improvement over CMB data alone can be several orders of magnitude. Dark matter-baryon scattering cannot affect the halo mass function on mass scales $M>{10}^{12}{M}_{\odot }$. Our results imply, model independently, that a baryon in the halo of a galaxy like our own Milky Way does not scatter from dark matter particles during the age of the galaxy.

The nature of the isotropic $\gamma$-ray background (IGRB) measured by the Large Area Telescope (LAT) on the Fermi $\gamma$-ray space telescope (Fermi) remains partially unexplained. Non-negligible contributions may originate from extragalactic populations of unresolved sources such as blazars, star-forming galaxies or galactic millisecond pulsars. A recent prediction of the diffuse $\gamma$-ray emission from active galactic nuclei (AGN) with a large viewing angle with respect to the line of sight has demonstrated that this faint but numerous population is also expected to contribute significantly to the total IGRB intensity. A more exotic contribution to the IGRB invokes the pair annihilation of dark matter (DM) weakly interacting massive particles (WIMPs) into $\gamma$ rays. In this work, we evaluate the room left for galactic DM at high latitudes ($>10^{\circ }$) by including photons from both prompt emission and inverse Compton scattering, emphasizing the impact of the newly discovered contribution from misaligned AGN (MAGN) for such an analysis. Summing up all significant galactic and extragalactic components of the IGRB, we find that an improved understanding of the associated astrophysical uncertainties is still mandatory to put stringent bounds on thermally produced DM. On the other hand, we also demonstrate that the IGRB has the potential to be one of the most competitive future ways to test the DM WIMP hypothesis, once the present uncertainties are even slightly reduced. In fact, if MAGN contribute even at 90% of the maximal level consistent with our current understanding, thermally produced WIMPs would be severely constrained as DM candidates for masses up to several TeV.

This paper explores the conditions under which modified gravitational theories admit positive mass. Following Witten’s spinor argument, it is argued that a single condition should be imposed upon a gauge connection in the supercovariant derivative. Under this condition, we present a simple formula for the divergence of the Nester tensor in Einstein’s gravity with a general source. Applying this prescription to the Einstein-scalar system, we find that for a certain class of the gauge connection, a special kind of noncanonical scalar-field theory admits the positivity property in addition to the ordinary canonical scalar-field system. In both cases, the scalar potential can be written in terms of a superpotential. In the noncanonical case, we obtain the most general Bogomol’nyi-Prasad-Sommerfield solutions which preserve at least half of the supersymmetry.

We studied the signatures of an electroweak SU(2) lepton triplet, which contains a doubly charged heavy lepton. The most interesting and easily detected final states originate from the doubly charged lepton pair and single production, which we analyzed at a center-of-mass energy of 14 TeV. We proposed useful kinematic cuts to reduce the backgrounds and computed the integrated luminosity needed to discover or exclude the doubly charged leptons for various masses.

After the recent discovery of a 125 GeV Higgs-like particle at the Large Hadron Collider (LHC), it is crucial to examine its role in unitarizing high energy $W_L{W}_L$ scattering, which may reveal its possible deviation from a Standard Model Higgs. We perform an updated study on $WW$ scattering in the semileptonic channel at the LHC, improved by the recently developed $W$ jet tagging method. The resultant statistical significance of a strongly interacting light Higgs model is about 20% larger than that based on the conventionally “gold-plated” dileptonic channel, while 200% more signal events are retained. The excellent sensitivity to the anomalous Higgs-$W$ boson coupling makes semileptonic $WW$ scattering an important complement to precision measurements at the Higgs resonance.

We derive bounds from oblique parameters on the dimension-6 operators of an effective field theory of electroweak gauge bosons and the Higgs doublet. The loop-induced contributions to the $\mathrm{\Delta }S$, $\mathrm{\Delta }T$, and $\mathrm{\Delta }U$ oblique parameters are sensitive to these contributions, and we pay particular attention to the role of renormalization when computing loop corrections in the effective theory. Limits on the coefficients of the effective theory from loop contributions to oblique parameters yield complementary information to direct Higgs production measurements.

The quark mass dependence of hadrons is an important input for lattice calculations. We investigate the light quark mass dependence of the binding energy of the $X(3872)$ and the ${\overline{D}}^0{D}^{*0}$ scattering length in the $C=+1$ channel to next-to-leading order in an effective field theory for the $X$ (XEFT) where pion interactions are perturbative. At this order, the quark mass dependence is determined by a quark mass-dependent contact interaction in addition to the one-pion exchange. Using naturalness arguments to constrain unknown parameters, we find a moderate sensitivity of the binding energy for quark masses up to twice the physical value while the scattering length is more sensitive. The occurrence of infrared divergences due to on-shell pions in XEFT and their treatment is discussed in detail.

A relativistic light-front quark model is used to describe both the elastic nucleon and nucleon-Roper transition form factors in a large $Q^2$ range, up to $35{\mathrm{GeV}}^2$ for the elastic and up to $\text{12\hspace{0.17em}\hspace{0.17em}}{\mathrm{GeV}}^2$ for the resonance case. Relativistic three-quark configurations satisfying the Pauli exclusion principle on the light front are used for the derivation of the current matrix elements. The Roper resonance is considered as a mixed state of a three-quark core configuration and a molecular $N+\sigma$ hadron component. Based on this ansatz we obtain a realistic description of both processes, elastic and inelastic, and show that existing experimental data are indicative of a composite structure of the Roper resonance.

Motivated by the recent high-precision lattice data on Yang-Mills equations of state, we propose an effective theory of SU(3) gluonic matter. The theory is constructed based on the center and scale symmetries and their dynamical breaking, so that the interplay between color-electric and color-magnetic gluons is included coherently. We suggest that the magnetic gluon condensate changes its thermal behavior qualitatively above the critical temperature as a consequence of matching to the dimensionally reduced magnetic theories. We consider thermodynamics in the mean field approximation and discuss the consequences for the interaction measure.

In this work we study the $D^{*}{\overline{D}}^{*}$ current with QCD sum rules. We write the correlation function using the general current corresponding to the $D^{*}{\overline{D}}^{*}$ system and then use spin projectors to obtain the correlation function in the $0^{+}$, $1^{+}$, and $2^{+}$ spin-parity configurations. The purpose of the present work is to investigate the possibility of explaining the recently reported $Z_c(4025)$ as a $D^{*}{\overline{D}}^{*}$ moleculelike state. As a result, we find a state for each spin case with a very similar mass: $M^{S=0}=(3943\pm 104)\mathrm{MeV}$, $M^{S=1}=(3950\pm 105)\mathrm{MeV}$, $M^{S=2}=(3946\pm 104)\mathrm{MeV}$. We discuss that our mass results, within error bars, for $1^{+}$ or $2^{+}$ are both compatible with $Z_c(4025)$. However, our results are also compatible with a possible $D^{*}{\overline{D}}^{*}$ bound state, in agreement with predictions of some previous works. We have also calculated the current-state coupling which turns out to be larger in the $2^{+}$ case.

We investigate new physics scenarios where systems comprised of a single top quark accompanied by missing transverse energy, dubbed monotops, can be produced at the LHC. Following a simplified model approach, we describe all possible monotop production modes via an effective theory and estimate the sensitivity of the LHC, assuming $20{\mathrm{fb}}^{-1}$ of collisions at a center-of-mass energy of 8 TeV, to the observation of a monotop state. Considering both leptonic and hadronic top quark decays, we show that large fractions of the parameter space are reachable and that new physics particles with masses ranging up to 1.5 TeV can leave hints within the 2012 LHC data set, assuming moderate new physics coupling strengths.

Analyses of boosted Higgs bosons from associated production comprise some of the main search channels for the Higgs boson at the LHC. The gluon-initiated $gg\to hZ$ subprocess has largely been ignored in phenomenological analyses of boosted associated production although this contribution is sizable as the $p_T$ spectrum for this process is maximized in the boosted regime due to the top quark loop threshold. In this paper, we discuss this contribution to boosted $pp\to hZ$ analyses in detail. We find there are previously overlooked modifications of standard model Higgs rates at the LHC which depend on the $p_T$ cuts applied and can be significant. There are also important consequences for physics beyond the standard model as the $gg\to hZ$ process introduces significant dependence on the magnitude and sign of the Higgs-top quark coupling $c_t$, which is overlooked if it is assumed that associated production depends only on the Higgs-$Z$ boson coupling as $c_V^2$. This new dependence on $c_t$ impacts interpretations of Higgs rates in the contexts of supersymmetry, two Higgs doublet models, and general scenarios with modified couplings. We suggest that these effects be included in current and future LHC boosted Higgs analyses.