The thermal evolution of the axial anomaly is investigated in the system of the linear sigma model for $2+1$ flavors. We explore the functional form of the effective potential and the coefficient of the ’t Hooft determinant term. It is found that the latter develops a nontrivial structure as a function of the chiral condensate and grows everywhere with respect to the temperature. This shows that mesonic fluctuations strengthen the axial anomaly at finite temperature and it does not vanish at the critical point. The phenomenon has been found to have significance in the thermal properties of the mesonic spectra, especially concerning the $\eta -{\eta }^{\prime }$ system.

The existence of a 750 GeV di-photon spin-0 resonance $S$ would imply the additional presence of new particles beyond the Standard Model, coupling directly to $S$ and electromagnetically charged. For an $SU(2{)}_{\mathrm{L}}$ singlet $S$, we explore the possibility of probing the $SU(2{)}_{\mathrm{L}}$ and $U(1{)}_{\mathrm{Y}}$ quantum numbers of the new states at the LHC by measuring and constraining the $WW$, $Z\gamma$, and $ZZ$ decays of $S$. We obtain robust prospects on the required LHC integrated luminosity to discover the new decay modes of $S$ and discuss the implications of these measurements for probing the electroweak nature of the new states. We also discuss the impact of $S$ mixing with the SM Higgs in such probes.

The recent LHC Run-2 data have shown a possible excess in diphoton events, suggesting the existence of a new resonance $\varphi$ with mass $M\sim 750\mathrm{GeV}$. If $\varphi$ plays the role of a portal particle connecting the Standard Model and the invisible dark sector, the diphoton excess should be correlated with another photon excess, namely, the excess in the diffuse gamma rays towards the Galactic Center, which can be interpreted by the annihilation of dark matter (DM). We investigate the necessary conditions for a consistent explanation for the two photon excesses, especially the requirement on the width-to-mass ratio $\mathrm{\Gamma }/M$ and $\varphi$ decay channels, in a collection of DM models where the DM particle can be scalar, fermionic, and vector, and $\varphi$ can be generated through $s$-channel $gg$ fusion or $q\overline{q}$ annihilation. We show that the minimally required $\mathrm{\Gamma }/M$ is determined by a single parameter proportional to $(m_{\chi }/M{)}^n$, where the integer $n$ depends on the nature of the DM particle. We find that for the scalar DM model with $\varphi$ generated from $q\overline{q}$ annihilation, the minimally required $\mathrm{\Gamma }/M$ can be as low as $\mathcal{O}(10^{-3})$. For the scalar DM model with $\varphi$ generated from $gg$ fusion and fermionic DM model with $\varphi$ from $q\overline{q}$ annihilation, the required $\mathrm{\Gamma }/M$ are typically of $\mathcal{O}(10^{-2})$. The vector DM models, however, require very large $\mathrm{\Gamma }/M$ of order one. For the DM models which can consistently explain both the excesses, the predicted cross sections for gamma-ray line are typically of $\mathcal{O}(10^{-31}–10^{-29}){\mathrm{cm}}^3{\mathrm{s}}^{-1}$, which are close to the current limits from the Fermi-LAT experiment.

The renormalizable coloron model, which has previously been shown in the literature to be consistent with a wide array of theoretical and precision electroweak constraints, includes a pair of spinless bosons (one scalar, one pseudoscalar). We show that either of them, or both together if they are degenerate, could be responsible for the diphoton resonance signal for which both CMS and ATLAS have seen evidence. Because either of these bosons would be produced and decay through loops of spectator fermions, the absence of signals in dijet, $t\overline{t}$, and electroweak boson pair channels is not a surprise.

Direct, resonant production of the charmonium states ${\chi }_{c1}$ and ${\chi }_{c2}$ in electron-positron annihilation is investigated. Depending on details of the model, a sizeable variation of the prediction for the production cross section is anticipated. It is demonstrated that resonant production could be observed under favorable circumstances.

The differential cross sections for inclusive neutral pions as a function of transverse and longitudinal momentum in the very forward-rapidity region have been measured at the LHC with the LHC forward detector in proton-proton collisions at $\sqrt{s}=2.76$ and 7 TeV and in proton-lead collisions at nucleon-nucleon center-of-mass energies of $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$. Such differential cross sections in proton-proton collisions are compatible with the hypotheses of limiting fragmentation and Feynman scaling. Comparing proton-proton with proton-lead collisions, we find a sizable suppression of the production of neutral pions in the differential cross sections after subtraction of ultraperipheral proton-lead collisions. This suppression corresponds to the nuclear modification factor value of about 0.1–0.3. The experimental measurements presented in this paper provide a benchmark for the hadronic interaction Monte Carlo simulation codes that are used for the simulation of cosmic ray air showers.

Measurements of the top-antitop quark pair production charge asymmetry in the dilepton channel, characterized by two high-$p_{\mathrm{T}}$ leptons (electrons or muons), are presented using data corresponding to an integrated luminosity of $20.3{\mathrm{fb}}^{-1}$ from $pp$ collisions at a center-of-mass energy $\sqrt{s}=8\mathrm{TeV}$ collected with the ATLAS detector at the Large Hadron Collider at CERN. Inclusive and differential measurements as a function of the invariant mass, transverse momentum, and longitudinal boost of the $t\overline{t}$ system are performed both in the full phase space and in a fiducial phase space closely matching the detector acceptance. Two observables are studied: $A_{\mathrm{C}}^{\ell \ell }$ based on the selected leptons and $A_{\mathrm{C}}^{t\overline{t}}$ based on the reconstructed $t\overline{t}$ final state. The inclusive asymmetries are measured in the full phase space to be $A_{\mathrm{C}}^{\ell \ell }=0.008\pm 0.006$ and $A_{\mathrm{C}}^{t\overline{t}}=0.021\pm 0.016$, which are in agreement with the Standard Model predictions of $A_{\mathrm{C}}^{\ell \ell }=0.0064\pm 0.0003$ and $A_{\mathrm{C}}^{t\overline{t}}=0.0111\pm 0.0004$.

Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses proton-proton collision data corresponding to an integrated luminosity of $3.2{\mathrm{fb}}^{-1}$ at $\sqrt{s}=13\mathrm{TeV}$ collected in 2015 with the ATLAS detector at the Large Hadron Collider. Events are required to have at least one jet with a transverse momentum above 250 GeV and no leptons. Several signal regions are considered with increasing missing-transverse-momentum requirements between $E_{\mathrm{T}}^{\mathrm{miss}}>250\mathrm{GeV}$ and $E_{\mathrm{T}}^{\mathrm{miss}}>700\mathrm{GeV}$. Good agreement is observed between the number of events in data and Standard Model predictions. The results are translated into exclusion limits in models with large extra spatial dimensions, pair production of weakly interacting dark-matter candidates, and the production of supersymmetric particles in several compressed scenarios.

We study a class of $\mathcal{N}=(1,0)$ little string theories obtained from orbifolds of M-brane configurations. These are realized in two different ways that are dual to each other: either as $M$ parallel M5-branes probing a transverse $A_{N-1}$ singularity or $N$ M5-branes probing an $A_{M-1}$ singularity. These backgrounds can further be dualized into toric, noncompact Calabi-Yau threefolds $X_{N,M}$ which have double elliptic fibrations and thus give a natural geometric description of T-duality of the little string theories. The little string partition functions are captured by the topological string partition function of $X_{N,M}$. We analyze in detail the free energies ${\mathrm{\Sigma }}_{N,M}$ associated with the latter in a special region in the Kähler moduli space of $X_{N,M}$ and discover a remarkable property: in the Nekrasov-Shatashvili limit, ${\mathrm{\Sigma }}_{N,M}$ is identical to $NM$ times ${\mathrm{\Sigma }}_{1,1}$. This entails that the Bogomol’nyi-Prasad-Sommerfield (BPS) degeneracies for any $(N,M)$ can uniquely be reconstructed from the $(N,M)=(1,1)$ configuration, a property we refer to as self-similarity. Moreover, as ${\mathrm{\Sigma }}_{1,1}$ is known to display a number of recursive structures, BPS degeneracies of little string configurations for arbitrary $(N,M)$ as well acquire additional symmetries. These symmetries suggest that in this special region the two little string theories described above are self-dual under T-duality.

The flatness of the inflaton potential and lightness of the Higgs boson could have the common origin of the breaking of a global symmetry. This scenario provides a unified framework of Goldstone inflation and composite Higgs models, where the inflaton and the Higgs particle both have a pseudo-Goldstone boson nature. The inflaton reheats the Universe via decays to the Higgs and subsequent secondzary production of other SM particles via the top and massive vector bosons. We find that inflationary predictions and perturbative reheating conditions are consistent with cosmic microwave background data for sub-Planckian values of the fields, as well as opening up the possibility of inflation at the TeV scale. We explore this exciting possibility, leading to an interplay between collider data cosmological constraints.

This paper presents the first calculation of the gravitational self-force on a small compact object on an eccentric equatorial orbit around a Kerr black hole to first order in the mass ratio. That is the pointwise correction to the object’s equations of motion (both conservative and dissipative) due to its own gravitational field, which is treated as a linear perturbation to the background Kerr spacetime generated by the much larger spinning black hole. The calculation builds on recent advances on constructing the local metric and self-force from solutions of the Teukolsky equation, which led to the calculation of the Detweiler-Barack-Sago redshift invariant on eccentric equatorial orbits around a Kerr black hole in a previous paper. After deriving the necessary expression to obtain the self-force from the Weyl scalar ${\psi }_4$, we perform several consistency checks of the method and numerical implementation, including a check of the balance law relating the orbital average of the self-force to the average flux of energy and angular momentum out of the system. Particular attention is paid to the pointwise convergence properties of the sum over frequency modes in our method, identifying a systematic inherent loss of precision that any frequency domain calculation of the self-force on eccentric orbits must overcome.

In the context of twin Higgs models, we study a simple mechanism that simultaneously generates asymmetries in the dark and visible sector through the out-of-equilibrium decay of a TeV-scale particle charged under a combination of baryon and twin baryon number. We predict the dark matter to be a 5 GeV twin baryon, which is easy to achieve because of the similarity between the two confinement scales. Dark matter is metastable and can decay to three quarks, yielding indirect detection signatures. The mechanism requires the introduction of a new colored particle, typically within the reach of the LHC, of which we study the rich collider phenomenology, including prompt and displaced dijets, multijets, monojets and monotops.

A detailed comparison of HERA data at low Bjorken-$x$ and low four-momentum-transfer squared, $Q^2$, with predictions based on $\ln Q^2$ evolution (DGLAP) in perturbative quantum chromodynamics suggests inadequacies of this framework. The standard DGLAP evolution was augmented by including an additional higher-twist term in the description of the longitudinal structure function, $F_{\mathrm{L}}$. This additional term, $F_{\mathrm{L}}{A}_{\mathrm{L}}^{\mathrm{HT}}/Q^2$, improves the description of the reduced cross sections significantly. The resulting predictions for $F_{\mathrm{L}}$ suggest that further corrections are required for $Q^2$ less than about $2{\mathrm{GeV}}^2$.

Working in the framework of the Standard Model effective field theory, we study chirality-flipping couplings of the top quark to Higgs and gauge bosons. We discuss in detail the renormalization-group evolution to lower energies and investigate direct and indirect contributions to high- and low-energy $CP$-conserving and $CP$-violating observables. Our analysis includes constraints from collider observables, precision electroweak tests, flavor physics, and electric dipole moments. We find that indirect probes are competitive or dominant for both $CP$-even and $CP$-odd observables, even after accounting for uncertainties associated with hadronic and nuclear matrix elements, illustrating the importance of including operator mixing in constraining the Standard Model effective field theory. We also study scenarios where multiple anomalous top couplings are generated at the high scale, showing that while the bounds on individual couplings relax, strong correlations among couplings survive. Finally, we find that enforcing minimal flavor violation does not significantly affect the bounds on the top couplings.

The spectrum of a relic gravitational wave (RGW) contains high-frequency divergences, which should be removed. We present a systematic study of the issue, based on the exact RGW solution that covers the five stages, from inflation to the acceleration, each being a power law expansion. We show that the present RGW consists of vacuum dominating at $f>10^{11}\mathrm{Hz}$ and graviton dominating at $f<10^{11}\mathrm{Hz}$, respectively. The gravitons are produced by the four cosmic transitions, mostly by the inflation-reheating one. We perform adiabatic regularization to remove vacuum divergences in three schemes: at present, at the end of inflation, and at horizon exit, to the second adiabatic order for the spectrum, and the fourth order for energy density and pressure. In the first scheme, a cutoff is needed to remove graviton divergences. We find that all three schemes yield the spectra of a similar profile, and the primordial spectrum defined far outside horizon during inflation is practically unaffected. We also regularize the gauge-invariant perturbed inflaton and the scalar curvature perturbation by the last two schemes, and find that the scalar spectra, the tensor-scalar ratio, and the consistency relation remain unchanged.

We study the phenomenological implications of the presence of two zeros in a magic neutrino mass matrix. We find that only two such patterns of the neutrino mass matrix are experimentally acceptable. We express all the neutrino observables as functions of one unknown phase $\varphi$ and two known parameters $\mathrm{\Delta }{m}_{12}^2$, $r=\mathrm{\Delta }{m}_{12}^2/\mathrm{\Delta }{m}_{23}^2$. In particular, we find ${\sin }^2{\theta }_{13}=(2/3)r/(1+r)$. We also present a mass model for the allowed textures based upon the group $A_4$ using the type $\mathrm{I}+\mathrm{II}$ seesaw mechanism.

In this article, we explore the low energy structure of a $U(3)$ gauge theory over spaces with fuzzy sphere(s) as extra dimensions. In particular, we determine the equivariant parametrization of the gauge fields, which transform either invariantly or as vectors under the combined action of $SU(2)$ rotations of the fuzzy spheres and those $U(3)$ gauge transformations generated by $SU(2)\subset U(3)$ carrying the spin 1 irreducible representation of $SU(2)$. The cases of a single fuzzy sphere $S_F^2$ and a particular direct sum of concentric fuzzy spheres, $S_F^{2\mathrm{Int}}$, covering the monopole bundle sectors with windings $\pm 1$ are treated in full and the low energy degrees of freedom for the gauge fields are obtained. Employing the parametrizations of the fields in the former case, we determine a low energy action by tracing over the fuzzy sphere and show that the emerging model is Abelian Higgs type with $U(1)\times U(1)$ gauge symmetry and possesses vortex solutions on ${\mathbb{R}}^2$, which we discuss in some detail. Generalization of our formulation to the equivariant parametrization of gauge fields in $U(n)$ theories is also briefly addressed.

We study the Yukawa unification, in particular, the unification of the Yukawa coupling constants of $b$ and $\tau$, in the framework of the supersymmetric (SUSY) model. We concentrate on the model in which the SUSY breaking scalar masses are of the order of the gravitino mass while the gaugino masses originate from the effect of anomaly mediation and hence are one-loop suppressed relative to the gravitino mass. We perform an accurate calculation of the Yukawa coupling constants of $b$ and $\tau$ at the grand unified theory (GUT) scale, including relevant renormalization group effects and threshold corrections. In particular, we study the renormalization group effects, taking into account the mass splittings among sfermions, gauginos, and the standard model particles. We found that the Yukawa coupling constant of $b$ at the GUT scale is about 70% of that of $\tau$ if there is no hierarchy between the sfermion masses and the gravitino mass. Our results suggest sizable threshold corrections to the Yukawa coupling constants at the GUT scale or significant suppressions of the sfermion masses relative to the gravitino mass.

We present a measurement of the top quark mass in $p\overline{p}$ collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider. The data were collected by the D0 experiment corresponding to an integrated luminosity of $9.7{\mathrm{fb}}^{-1}$. The matrix element technique is applied to $t\overline{t}$ events in the final state containing leptons (electrons or muons) with high transverse momenta and at least two jets. The calibration of the jet energy scale determined in the $\mathrm{lepton}+\text{jets}$ final state of $t\overline{t}$ decays is applied to jet energies. This correction provides a substantial reduction in systematic uncertainties. We obtain a top quark mass of $m_t=173.93\pm 1.84\mathrm{GeV}$.

We study Weyl symmetry (local conformal symmetry) in unimodular gravity. It is shown that the Noether currents for both Weyl symmetry and global scale symmetry vanish exactly as in conformally invariant scalar-tensor gravity. We clearly explain why in the class of conformally invariant gravitational theories, the Noether currents vanish by starting with conformally invariant scalar-tensor gravity. Moreover, we comment on both classical and quantum-mechanical equivalences in Einstein’s general relativity, conformally invariant scalar-tensor gravity, and the Weyl-transverse gravity. Finally, we discuss the Weyl current in the conformally invariant scalar action and see that it is also vanishing.