We elucidate and extend the conditions that map gauge-Yukawa theories at low energies into time-honored gauged four-fermion interactions at high energies. These compositeness conditions permit us to investigate theories of composite dynamics through gauge-Yukawa theories. Here we investigate whether perturbative gauge-Yukawa theories can have a strongly coupled limit at high energy that can be mapped into a four-fermion theory. Interestingly, we are able to precisely carve out a region of the perturbative parameter space supporting such a composite limit. This has interesting implications on our current view on models of particle physics. As a template model we use an $SU(N_C)$ gauge theory with $N_F$ Dirac fermions transforming according to the fundamental representation of the gauge group. The fermions further interact with a gauge singlet complex $N_F\times N_F$ Higgs boson that ceases to be a physical degree of freedom at the ultraviolet composite scale, where it gives away to the four-fermion interactions. We compute the hierarchy between the ultraviolet and infrared composite scales of the theory and show that they are naturally large and well separated. Our results show that some weakly coupled gauge-Yukawa theories can be viewed, in fact, as composite theories. It is therefore tantalizing to speculate that the standard model, with its phenomenological perturbative Higgs sector, could hide, in plain sight, a composite theory.

In the present paper the electrostatics of charges in nonrotating BTZ black hole and wormhole spacetimes is studied. Our attention is focused on the self-force of a point charge in the geometry, for which a regularization prescription based on the Haddamard Green function is employed. The differences between the self-force in both cases is a theoretical experiment for distinguishing both geometries, which otherwise are locally indistinguishable. This idea was applied before to four and higher-dimensional black holes by the present and other authors. However, the particularities of the BTZ geometry makes the analysis considerable more complicated than those. First, the BTZ spacetimes are not asymptotically flat but instead asymptotically AdS. In addition, the relative distance $d(r,r+1)$ between two particles located at a radius $r$ and $r+1$ in the geometry tends to zero when $r\to \infty$. This behavior, which is radically different in a flat geometry, changes the analysis of the asymptotic conditions for the electrostatic field. The other problem is that there exist several regularization methods other than the one we are employing, and there does not exist a proof in three dimensions that they are equivalent. However, we focus on the Haddamard method and obtain an expression for the hypothetical self-force in series, and the resulting expansion is convergent to the real solution. We suspect that the convergence is not uniform, and furthermore there are no summation formulas at our disposal. It appears, for points that are far away from the black hole the calculation of the Haddamard self-force requires higher-order summation. These subtleties are carefully analyzed in the paper, and it is shown that they lead to severe problems when calculating the Haddamard self-force for asymptotic points in the geometry.

We study the problem of decoupling of heavy chiral superfields in four-dimensional $N=1$ supersymmetric field theories with Lorentz-invariant and Lorentz-violating higher-derivative terms. We demonstrate that the earlier found effect of large logarithmic quantum corrections, due to heavy chiral superfields, takes place not only if the theory possesses quantum divergences, but also for essentially finite theories involving higher-derivative terms, both Lorentz-invariant and Lorentz-breaking ones.

Anomaly-free perturbations of loop quantum cosmology reveal a deformed space-time structure, in which the signature changes when the energy density is $\rho ={\rho }_c/2$. Furthermore, in loop quantum cosmology, one can obtain an effective causal structure only for a low density region ($\rho \le {\rho }_c/2$), which gives a natural initial condition to consider the horizon problem. Choosing the initial value at $\rho (0)={\rho }_c/2$ in this paper, we investigate the horizon problem and the probability of inflation in the framework of loop quantum cosmology. Two models are considered: the quadratic inflation and the natural inflation. We use the Liouville measure to calculate the probability of inflation which solves the horizon problem, and find that, for the quadratic inflation model, the probability is very close to unity, while for the natural inflation model, the probability is about 35%.

We study the average rate of change of energy for a static atom immersed in a thermal bath of electromagnetic radiation in the cosmic string spacetime and separately calculate the contributions of thermal fluctuations and radiation reaction. We find that the transition rates are crucially dependent on the atom-string distance and polarization of the atom and they in general oscillate as the atom-string distance varies. Moreover, the atomic transition rates in the cosmic string spacetime can be larger or smaller than those in Minkowski spacetime contingent upon the atomic polarization and position. In particular, when located on the string, ground-state atoms can make a transition to excited states only if they are polarizable parallel to the string, whereas ground-state atoms polarizable only perpendicular to the string are stable as if they were in a vacuum, even if they are immersed in a thermal bath. Our results suggest that the influence of a cosmic string is very similar to that of a reflecting boundary in Minkowski spacetime.

We investigate the limits of applicability of the quasistatic approximation in cosmologies featuring general models of dark energy or modified gravity. We show that, at best, the quasistatic approximation breaks down outside of the sound horizon of the dark-energy, rather than the cosmological horizon as is frequently assumed. When the sound speed of dark energy is significantly below that of light, the quasistatic limit is only valid in a limited range of observable scales and this must be taken into account when computing effects on observations in such models. As an order of magnitude estimate, in the analysis of data from today’s weak-lensing and peculiar-velocity surveys, dark energy can be modeled as quasistatic only if the sound speed is larger than order 1% of that of light. In upcoming surveys, such as Euclid, it should only be used when the sound speed exceeds around 10% of the speed of light. In the analysis of the cosmic microwave background, the quasistatic limit should never be used for the integrated Sachs-Wolf effect and for lensing only when the sound speed exceeds 10% of the speed of light.

The effective description of loop quantum cosmology (LQC) has proved to be a convenient platform to study phenomenological implications of the quantum bounce that resolves the classical big bang singularity. Originally, this description was derived using Gaussian quantum states with small dispersions. In this paper we present a generalization to incorporate states with large dispersions. Specifically, we derive the generalized effective Friedmann and Raychaudhuri equations and propose a generalized effective Hamiltonian which are being used in an ongoing study of the phenomenological consequences of a broad class of quantum geometries. We also discuss an interesting interplay between the physics of states with larger dispersions in standard LQC, and of sharply peaked states in (hypothetical) LQC theories with larger area gap.

The maximal Arnowitt-Deser-Misner (ADM) mass for (mini)boson stars (BSs)—gravitating solitons of Einstein’s gravity minimally coupled to a free, complex, mass $\mu$, Klein-Gordon field—is $M_{\mathrm{ADM}}^{\max }\sim M_{\text{Pl}}^2/\mu$. Adding quartic self-interactions to the scalar field theory, described by the Lagrangian ${\mathcal{L}}_I=\lambda |\mathrm{\Psi }{|}^4$, the maximal ADM mass becomes $M_{\mathrm{ADM}}^{\max }\sim \sqrt{\lambda }{M}_{\text{Pl}}^3/{\mu }^2$. Thus, for mini-BSs, astrophysically interesting masses require ultralight scalar fields, whereas self-interacting BSs can reach such values for bosonic particles with Standard Model range masses. We investigate how these same self-interactions affect Kerr black holes with scalar hair (KBHsSH) [C. A. R. Herdeiro and E. Radu, Kerr Black Holes with Scalar Hair, Phys. Rev. Lett. 112, 221101 (2014).], which can be regarded as (spinning) BSs in stationary equilibrium with a central horizon. Remarkably, whereas the ADM mass scales in the same way as for BSs, the horizon mass $M_H$ does not increases with the coupling $\lambda$, and, for fixed $\mu$, it is maximized at the “Hod point,” corresponding to the extremal Kerr black hole obtained in the vanishing hair limit. This mass is always $M_{\mathrm{H}}^{\max }\sim M_{\text{Pl}}^2/\mu$. Thus, introducing these self-interactions, the black hole spacetimes may become considerably “hairier” but the trapped regions cannot become “heavier.” We present evidence that this observation also holds in a model with ${\mathcal{L}}_I=\beta |\mathrm{\Psi }{|}^6-\lambda |\mathrm{\Psi }{|}^4$; if it extends to general scalar field models, KBHsSH with astrophysically interesting horizon masses require ultralight scalar fields. Their existence, therefore, would be a smoking gun for such (beyond the Standard Model) particles.

We use the spherical collapse method to investigate the nonlinear density perturbations of pressureless matter in the cosmological models with the extended quintessence as dark energy in the metric and Palatini formalisms. We find that for both formalisms, when the coupling constant is negative, the deviation from the $\mathrm{\Lambda }\mathrm{CDM}$ model is the least according to the evolutionary curves of the linear density contrast ${\delta }_c$ and virial overdensity ${\mathrm{\Delta }}_v$, and it is less than 1%. And this indicates that, in the extended quintessence cosmological models in which the coupling constant is negative, all quantities dependent on ${\delta }_c$ or ${\mathrm{\Delta }}_v$ are essentially unaffected if the linear density contrast or the virial overdensity of the $\mathrm{\Lambda }\mathrm{CDM}$ model is used as an approximation. Moreover, we find that the differences between different formalisms are very small in terms of structure formation, and thus cannot be used to distinguish the metric and Palatini formalisms.

We explore the effects of elastic scattering between dark matter and baryons on the 21-cm signal during the dark ages. In particular, we consider a dark-matter–baryon interaction with a cross section of the form $\sigma ={\sigma }_0{v}^{-4}$, in which case the effect of the drag force between the dark matter and baryon fluids grows with time. We show that, as opposed to what was previously thought, this effect heats up the baryons due to the relative velocity between dark matter and baryons. This creates an additional source of fluctuations, which can potentially make interactions easier to detect by 21-cm measurements than by using the cosmic microwave background and the Lyman-$\alpha$ forest. Our forecasts show that the magnitude of the cross section can be probed to ${\sigma }_0\sim 3\times 10^{-42}{\mathrm{cm}}^2$ for $m_{\chi }\ll 1\mathrm{GeV}$ and ${\sigma }_0\sim 2\times 10^{-41}(m_{\chi }/10\mathrm{GeV}){\mathrm{cm}}^2$ for $m_{\chi }\gg 1\mathrm{GeV}$ with next generation experiments, and improved to ${\sigma }_0\sim 4\times 10^{-44}{\mathrm{cm}}^2$ for $m_{\chi }\ll 1\mathrm{GeV}$ and ${\sigma }_0\sim 4\times 10^{-43}(m_{\chi }/10\mathrm{GeV}){\mathrm{cm}}^2$ for $m_{\chi }\gg 1\mathrm{GeV}$ with futuristic experiments.

We investigate how the extragalactic proton component derived within the “escape model” can be explained by astrophysical sources. We consider as possible cosmic ray (CR) sources normal or starburst galaxies and radio-loud active galactic nuclei (AGN). We find that the contribution to the total extragalactic proton flux from normal and starburst galaxies is only subdominant and does not fit the spectral shape deduced in the escape model. In the case of radio-loud AGN, we show that the complete extragalactic proton spectrum can be explained by a single source population, BL Lac/FR I, for any of the potential acceleration sites in these sources. We calculate the diffuse neutrino and $\gamma$-ray fluxes produced by these CR protons interacting with gas inside their sources. For a spectral slope of CRs close to $\alpha =2.1–2.2$ as suggested by shock acceleration, we find that these UHECR sources contribute the dominant fraction of both the isotropic $\gamma$-ray background and of the extragalactic part of the astrophysical neutrino signal observed by IceCube.

We revisit the topic of triple-product asymmetries which probe $CP$ violation through differential distributions. We construct distributions with well-defined discrete symmetry properties and characterize the asymmetries formed upon them. It is stressed that the simplest asymmetries may not be optimal. We explore systematic generalizations having limited reliance on the process dynamics and phase-space parametrization. They exploit larger fractions of the information contained in differential distributions and may lead to increased sensitivities to $CP$ violation. Our detailed treatment of the case of spinless four-body decays paves the way for further experimental studies.

Run 1 data of the Large Hadron Collider (LHC) contain excessive events in the same-sign dilepton channel with $b$-jets and missing transverse energy (MET), which were observed by five separate analyses from the ATLAS and CMS collaborations. We show that these events could be explained by direct production of top squarks in supersymmetry. In particular, a right-handed top squark with a mass of 550 GeV decaying into 2 $t$ quarks, 2 $W$ bosons, and MET could fit the observed excess without being constrained by other direct search limits from Run 1. We propose kinematic cuts at 13 TeV to enhance the top squark signal, and estimate that top squarks could be discovered with $40{\mathrm{fb}}^{-1}$ of integrated luminosity at Run 2 of the LHC, when considering only the statistical uncertainty.

We analyze the prospect of extending the reach for squarks and gauginos via associated production at a $\sqrt{s}=100\mathrm{TeV}$ proton-proton collider, given $3{\mathrm{ab}}^{-1}$ integrated luminosity. Depending on the gluino mass, the discovery reach for squarks in associated production with a gluino can be up to 37 TeV for compressed spectra (small gluino-lightest supersymmetric particle (LSP) mass splitting), and up to 32 TeV for noncompressed spectra. The discovery reach for Winos can be up to between 3.5 and 6 TeV depending on squark masses and Wino decay kinematics. Binos of up to 1.7 TeV could similarly be discovered. Squark-gaugino associated production could prove to be the discovery mode for supersymmetry at a 100 TeV collider in a large region of parameter space.

We obtain prompt diphoton cross section in proton-nucleus collisions in Hamiltonian light-cone approach within a hybrid approximation, treating the projectile proton in the parton model and the target nucleus in the color-glass-condensate approach. We study in detail the diphoton correlations in quark-nucleus and proton-nucleus collisions at RHIC and the LHC. We show that the single fragmentation diphoton produces the away-side correlations peak, and the double-fragmentation component of prompt diphoton is responsible for the near-side peak, and the long-range in rapidity near-side azimuthal collimation, the so-called “ridge” structure. We study the transverse momentum, density and energy dependence of the diphoton ridge and show that it strongly depends on the kinematics and saturation dynamics. We show that while diphoton ridge exists at the LHC in quark-nucleus collisions, the effect disappears in proton-nucleus collisions at the LHC. At RHIC the ridge-type structure persists at low transverse momenta of diphoton even in proton-nucleus collisions. We argue that diphoton correlation measurements in $\mathrm{p}+\mathrm{A}$ collisions can help to discriminate among models and understand the true origin of the observed dihadron ridge in $\mathrm{p}+\mathrm{A}$ collisions. We also show that in addition to the ridge structure, prompt diphoton correlation also exhibits some distinct novel features, including the emergence of away-side double-peak structure at intermediate transverse momenta.

We find that the evolution equation for the three-particle quark-gluon $B$-meson light-cone distribution amplitude (DA) of subleading twist is completely integrable in the large $N_c$ limit and can be solved exactly. The lowest anomalous dimension is separated from the remaining, continuous spectrum by a finite gap. The corresponding eigenfunction coincides with the contribution of quark-gluon states to the two-particle DA ${\varphi }_{-}(\omega )$ so that the evolution equation for the latter is the same as for the leading-twist DA ${\varphi }_{+}(\omega )$ up to a constant shift in the anomalous dimension. Thus, “genuine” three-particle states that belong to the continuous spectrum effectively decouple from ${\varphi }_{-}(\omega )$ to the leading-order accuracy. In turn, the scale dependence of the full three-particle DA turns out to be nontrivial so that the contribution with the lowest anomalous dimension does not become leading at any scale. The results are illustrated on a simple model that can be used in studies of $1/m_b$ corrections to heavy-meson decays in the framework of QCD factorization or light-cone sum rules.

We present continuum extrapolated lattice QCD results for up to fourth-order diagonal and off-diagonal quark number susceptibilities in the high temperature region of 300–700 MeV. Lattice QCD calculations are performed using $2+1$ flavors of highly improved staggered quarks with nearly physical quark masses and at four different lattice spacings. Comparisons of our results with recent weak coupling calculations yield reasonably good agreements for the entire temperature range.

We compute leading-power fragmentation corrections to $J/\psi$ photoproduction at DESY HERA, making use of the nonrelativistic QCD factorization approach. Our calculations include parton production cross sections through order ${\alpha }_s^3$, fragmentation functions though order ${\alpha }_s^2$, and leading logarithms of the transverse momentum divided by the charm-quark mass to all orders in ${\alpha }_s$. We find that the leading-power fragmentation corrections, beyond those that are included through next-to-leading order in ${\alpha }_s$, are small relative to the fixed-order contributions through next-to-leading order in ${\alpha }_s$. Consequently, an important discrepancy remains between the experimental measurements of the $J/\psi$ photoproduction cross section and predictions that make use of nonrelativistic-QCD long-distance matrix elements that are extracted from the $J/\psi$ hadroproduction cross-section and polarization data.

We present theories of “natural neutrinos” in which neutral fermionic top partner fields are simultaneously the right-handed neutrinos (RHN), linking seemingly disparate aspects of the Standard Model structure: (a) The RHN top partners are responsible for the observed small neutrino masses, (b) they help ameliorate the tuning in the weak scale and address the little hierarchy problem, and (c) the factor of 3 arising from $N_c$ in the top-loop Higgs mass corrections is countered by a factor of 3 from the number of vectorlike generations of RHN. The RHN top partners may arise in pseudo-Nambu-Goldstone-Boson Higgs models such as the twin Higgs, as well as more general composite, little, and orbifold Higgs scenarios, and three simple example models are presented. This framework firmly predicts a TeV-scale seesaw, as the RHN masses are bounded to be below the TeV scale by naturalness. The generation of light neutrino masses relies on a collective breaking of the lepton number, allowing for comparatively large neutrino Yukawa couplings and a rich associated phenomenology. The structure of the neutrino mass mechanism realizes in certain limits the inverse or linear classes of seesaw. Natural neutrino models are testable at a variety of current and future experiments, particularly in tests of lepton universality, searches for lepton flavor violation, and precision electroweak and Higgs coupling measurements possible at high energy $e^{+}{e}^{-}$ and hadron colliders.