The first data from the LHC run 2 have shown a possible excess in diphoton events with invariant mass $\sim 750\mathrm{GeV}$, suggesting the existence of a new resonance which may decay dominantly into dark matter (DM) particles. We show in a simple model that the reported diphoton excess at the LHC is consistent with another photon excess, the 2 GeV excess in cosmic gamma-ray fluxes towards the Galactic Center observed by the Fermi-LAT. Both the excesses can be simultaneously explained by a $\sim 60\mathrm{GeV}$ scalar DM particle annihilating dominantly into two gluons with a typical thermal annihilation cross section, which leads to the prediction of a width-to-mass ratio $\mathrm{\Gamma }/M\approx \mathcal{O}({10}^{-2})$ of the resonance. The upper limit on the dijet search at LHC run 1 leads to a lower limit on the predicted cross section for DM annihilating into $\gamma \gamma$ final states $⟨\sigma v{⟩}_{\gamma \gamma }\gtrsim \mathcal{O}({10}^{-30}){\mathrm{cm}}^3{\mathrm{s}}^{-1}$. Both the predictions can be tested by the LHC, Fermi-LAT, and future experiments.

Recently the ATLAS and CMS Collaborations have reported evidence of a diphoton excess which may be interpreted as a pseudoscalar boson $S$ with a mass around 750 GeV. To explain the diphoton excess, such a boson is coupled to the Standard Model gauge fields via $SF\tilde{F}$ operators. In this work, we consider the implications of this state for early universe cosmology; in particular, the $S$ field can acquire a large vacuum expectation value due to quantum fluctuations during inflation. During reheating, it then relaxes to its equilibrium value, during which time the same operators introduced to explain the diphoton excess induce a nonzero chemical potential for baryon and lepton number. Interactions such as those involving right-handed neutrinos allow the system to develop a nonzero lepton number and, therefore, this state may also be responsible for the observed cosmological matter-antimatter asymmetry.

Pure compact $U(1)$ lattice gauge theory exhibits a phase transition at gauge coupling $g\sim \mathcal{O}(1)$ separating a familiar weak coupling Coulomb phase, having free massless photons, from a strong coupling phase. However, the phase transition was found to be of first order, ruling out any nontrivial theory resulting from a continuum limit from the strong coupling side. In this work, a compact $U(1)$ lattice gauge theory is studied with addition of a dimension-two mass counterterm and a higher derivative (HD) term that ensures a unique vacuum and produces a covariant gauge-fixing term in the naive continuum limit. For a reasonably large coefficient of the HD term, now there exists a continuous transition from a regular ordered phase to a spatially modulated ordered phase. For weak gauge couplings, a continuum limit from the regular ordered phase results in a familiar theory consisting of free massless photons. For strong gauge couplings with $g\ge \mathcal{O}(1)$, this transition changes from first order to continuous as the coefficient of the HD term is increased, resulting in tricritical points which appear to be a candidate in this theory for a possible nontrivial continuum limit.

We apply the higher-order tensor renormalization group to the lattice $\mathrm{CP}(N-1)$ model in two dimensions. A tensor network representation of the $\mathrm{CP}(N-1)$ model in the presence of the $\theta$ term is derived. We confirm that the numerical results of the CP(1) model without the $\theta$ term using this method are consistent with that of the O(3) model which is analyzed by the same method in the region $\beta \gg 1$ and that obtained by the Monte Carlo simulation in a wider range of $\beta$. The numerical computation including the $\theta$ term is left for future challenges.

We construct a potential obtained by one-pion exchange for the coupled channel ${\mathrm{\Sigma }}_c^{*}\overline{D}\text{−}{\mathrm{\Sigma }}_c{\overline{D}}^{*}$ and solve the coupled Schrödinger equations to determine the binding energy. We find that there exists one or two bound states with the binding energy of several MeV below the threshold of ${\mathrm{\Sigma }}_c^{*}$ and $\overline{D}$, dominantly made from a ${\mathrm{\Sigma }}_c^{*}$ baryon and a $\overline{D}$ meson, with the size of about 1.5 fm for a wide parameter region. We also study the pentaquark states including a $b$ quark and/or an anti-$b$ quark. We show that there exist pentaquarks including $c\overline{b}$, $b\overline{c}$, and $b\overline{b}$, all of which lie at about 10 MeV below the corresponding threshold and have size of about 1.5 fm.

To gain some sense about the likelihood of measuring the Higgs boson quartic coupling, we calculate the contribution to the triple Higgs production cross section from the subprocesses $q\overline{q}\to ZHHH$ and $q{\overline{q}}^{\prime }\to WHHH$. Our results illustrate that determining this coupling, or even providing experimental evidence that it exists, will be very difficult.

A class of exact conformastatic solutions of the Einstein-Maxwell field equations is presented in which the gravitational and electromagnetic potentials are completely determined by a harmonic function. We derive the equations of motion for neutral and charged particles in a spacetime background characterized by this class of solutions. As an example, we focus on the analysis of a particular harmonic function, which generates a singularity-free and asymptotically flat spacetime that describes the gravitational field of a punctual mass endowed with a magnetic field. In this particular case, we investigate the main physical properties of equatorial circular orbits. We show that due to the electromagnetic interaction, it is possible to have charged test particles which stay at rest with respect to a static observer located at infinity. Additionally, we obtain an analytic expression for the perihelion advance of test particles and the corresponding explicit value in the case of a punctual magnetic mass. We show that the analytical expressions obtained from our analysis are sufficient for being confronted with observations in order to establish whether such objects can exist in nature.

We study cosmological tensor perturbations on a quantized background within the hybrid quantization approach. In particular, we consider a flat, homogeneous and isotropic spacetime and small tensor inhomogeneities on it. We truncate the action to second order in the perturbations. The dynamics is ruled by a homogeneous scalar constraint. We carry out a canonical transformation in the system where the Hamiltonian for the tensor perturbations takes a canonical form. The new tensor modes now admit a standard Fock quantization with a unitary dynamics. We then combine this representation with a generic quantum scheme for the homogeneous sector. We adopt a Born-Oppenheimer ansatz for the solutions to the constraint operator, previously employed to study the dynamics of scalar inhomogeneities. We analyze the approximations that allow us to recover, on the one hand, a Schrödinger equation similar to the one emerging in the dressed metric approach and, on the other hand, the ones necessary for the effective evolution equations of these primordial tensor modes within the hybrid approach to be valid. Finally, we consider loop quantum cosmology as an example where these quantization techniques can be applied and compare with other approaches.

Searching for gravitational waves (GWs) from binary black holes (BBHs) with LIGO and Virgo involves matched-filtering data against a set of representative signal waveforms—a template bank—chosen to cover the full signal space of interest with as few template waveforms as possible. Although the component black holes may have significant angular momenta (spin), previous searches for BBHs have filtered LIGO and Virgo data using only waveforms where both component spins are zero. This leads to a loss of signal-to-noise ratio for signals where this is not the case. Combining the best available template placement techniques and waveform models, we construct a template bank of GW signals from BBHs with component spins ${\chi }_{1,2}\in [-0.99,0.99]$ aligned with the orbital angular momentum, component masses $m_{1,2}\in [2,48]{\mathrm{M}}_{\odot }$, and total mass $M_{\text{total}}\le 50{\mathrm{M}}_{\odot }$. Using effective-one-body waveforms with spin effects, we show that less than 3% of the maximum signal-to-noise ratio (SNR) of these signals is lost due to the discreetness of the bank, using the early Advanced LIGO noise curve. We use simulated Advanced LIGO noise to compare the sensitivity of this bank to a nonspinning bank covering the same parameter space. In doing so, we consider the competing effects between improved SNR and signal-based vetoes and the increase in the rate of false alarms of the aligned-spin bank due to covering a larger parameter space. We find that the aligned-spin bank can be a factor of 1.3–5 more sensitive than a nonspinning bank to BBHs with dimensionless spins $>+0.6$ and component masses $\gtrsim 20{\mathrm{M}}_{\odot }$. Even larger gains are obtained for systems with equally high spins but smaller component masses.

We compute the non-Gaussian contribution to the covariance of the matter power spectrum at one-loop order in standard perturbation theory (SPT), using the framework of the effective field theory (EFT) of large scale structure (LSS). The complete one-loop contributions are evaluated for the first time, including the leading EFT corrections that involve seven independent operators, of which four appear in the power spectrum and bispectrum. We compare the non-Gaussian part of the one-loop covariance computed with both SPT and EFT of LSS to two separate simulations. In one simulation, we find that the one-loop prediction from SPT reproduces the simulation well to $k_i+k_j\sim 0.25\mathrm{h}/\mathrm{Mpc}$, while in the other simulation we find a substantial improvement of EFT of LSS (with one free parameter) over SPT, more than doubling the range of $k$ where the theory accurately reproduces the simulation. The disagreement between these two simulations points to unaccounted for systematics, highlighting the need for improved numerical and analytic understanding of the covariance.

In a previous study, we have shown that spectral and anisotropy properties of IceCube astrophysical neutrino signals reveal evidence for a sizeable Galactic contribution to the neutrino flux in the Southern Hemisphere. We check if the Galactic contribution is detectable in the astrophysical muon neutrino flux observed from a low positive declinations region of the Northern sky. Estimating the Galactic neutrino flux in this part of the sky from $\gamma$-ray and Southern sky neutrino data, we find that the Northern sky astrophysical muon neutrino signal shows an excess over the Galactic flux. This points to the presence of an additional hard spectrum (extragalactic or large-scale Galactic halo) component of the astrophysical neutrino flux. We show that the Galactic flux component should still be detectable in the muon neutrino data in a decade-long IceCube exposure.

The scalar particle discovered at the Large Hadron Collider (LHC) has properties very similar to that of a standard model (SM) Higgs boson. Limited experimental knowledge of its model origin, as of now, however, does not rule out the possibility of accommodating this new particle into a beyond the SM (BSM) framework. A few of these schemes suggest that the observed scalar is just the lightest candidate of an enriched sector with several other heavier states awaiting to be detected. Such models with nonminimal scalar sector also accommodate other neutral and electrically charged (singly, doubly, triply, etc.) component fields as prescribed by the specific model. Depending on the mass and electric charge, these new states can produce potential signatures at colliders as well as in low-energy experiments. The presence of a doubly charged scalar, when accompanied by other neutral or charged scalar(s), can also generate neutrino masses. Adopting the second scenario, e.g., Babu-Zee construction, constraints from neutrino physics have been effaced in this study. Here, we investigate a few phenomenological consequences of a uncolored doubly charged scalar which couples to the charged leptons as well as gauge bosons. Restricting ourselves in the regime of conserved charged-parity ($CP$), we assume only a few nonzero Yukawa couplings ($y_{\mu \ell }$, where $\ell =e$, $\mu$, $\tau$) between the doubly charged scalar and the charged leptons. Our choices allow the doubly charged scalar to impinge low-energy processes like anomalous magnetic moment of muon and a few possible charged lepton flavor violating (CLFV) processes. These same Yukawa couplings are also instrumental in producing same-sign dilepton signatures at the LHC. In this article we examine the impact of individual contributions from the diagonal and off-diagonal Yukawa couplings in the light of muon ($g-2$) excess. Subsequently, we use the derived information to inquire the possible CLFV processes and finally the collider signals from the decay of a doubly charged scalar. Our simplified analyses, depending on the mass of doubly charged scalar, provide a good estimate for the magnitude of the concerned Yukawa couplings. Our findings would appear resourceful to test the phenomenological significance of a doubly charged scalar by using complementary information from muon ($g-2$), CLFV and the collider experiments.

We study the free energy of a static quark in QCD with $2+1$ flavors in a wide temperature region, $116\mathrm{MeV}<T<5814\mathrm{MeV}$, using the highly improved staggered quark (HISQ) action. We analyze the transition region in detail, obtain the entropy of a static quark, show that it peaks at temperatures close to the chiral crossover temperature and also revisit the temperature dependence of the Polyakov loop susceptibilities using gradient flow. We discuss the implications of our findings for the deconfinement and chiral crossover phenomena at physical values of the quark masses. Finally a comparison of the lattice results at high temperatures with the weak-coupling calculations is presented.

We present how a neutrino condensate and small neutrino masses emerge from a topological formulation of gravitational anomaly. We first recapitulate how a gravitational $\theta$-term leads to the emergence of a new bound neutrino state analogous to the ${\eta }^{\prime }$ meson of QCD. Then we show the consequent formation of a neutrino vacuum condensate, which effectively generates small neutrino masses. Afterwards we outline numerous phenomenological consequences of our neutrino mass generation model. The cosmological neutrino mass bound vanishes since we predict the neutrinos to be massless until the phase transition in the late Universe, $T\sim \mathrm{meV}$. Coherent radiation of new light particles in the neutrino sector can be detected in prospective precision experiments. Deviations from an equal flavor rate due to enhanced neutrino decays in extraterrestrial neutrino fluxes can be observed in future IceCube data. These neutrino decays may also necessitate modified analyses of the original neutrino spectra of the supernova SN 1987A. The current cosmological neutrino background only consists of the lightest neutrinos, which, due to enhanced neutrino-neutrino interactions, either bind up, form a superfluid, or completely annihilate into massless bosons. Strongly coupled relic neutrinos could provide a contribution to cold dark matter in the late Universe, together with the new proposed particles and topological defects, which may have formed during neutrino condensation. These enhanced interactions could also be a source of relic neutrino clustering in our Galaxy, which possibly makes the overdense cosmic neutrino background detectable in the KATRIN experiment. The neutrino condensate provides a mass for the hypothetical $B-L$ gauge boson, leading to a gravity-competing force detectable in short-distance measurements. Prospective measurements of the polarization intensities of gravitational waves can falsify our neutrino mass generation model.

Cyclic symmetry in the neutrino sector with the type-I seesaw mechanism in the mass basis of charged leptons and right chiral neutrinos ($N_{iR}$, $i=e$, $\mu$, $\tau$) generates a twofold degenerate light neutrino and a threefold degenerate heavy neutrino mass spectrum. Consequently, such a scheme produces vanishing one light neutrino mass squared difference and lepton asymmetry. To circumvent such an unphysical outcome, we break cyclic symmetry in the diagonal right chiral neutrino mass term by a small breaking parameter. Nonzero mass squared differences and mixing angles are generated with the help of the small breaking parameter. The smallness of the breaking parameter opens up the possibility of resonant leptogenesis. Assuming complex Yukawa couplings, we derive generalized expressions with flavor-dependent $CP$ asymmetry parameters (${ϵ}_i^{\alpha }$) which are valid for the quasidegenerate as well as hierarchical mass spectrum of right-handed neutrinos. Thereafter, we set up the chain of coupled Boltzmann equations (which are flavor dependent too) which have to be solved in order to get the final lepton asymmetries. Depending upon the temperature regime, the $CP$ asymmetries and the Boltzmann equations may also be flavor independent. As our goal is to study the enhancement of $CP$ asymmetry due to the quasidegeneracy of right-handed neutrinos, we select only the lowest allowed (by neutrino oscillation data) value of the breaking parameter (and other corresponding Lagrangian parameters) and estimate the baryon asymmetry parameter $Y_B$. The experimental constraint of $Y_B$ introduces a bound on right-handed neutrino mass which remained unrestricted by neutrino oscillation data.

We measure the forward–backward asymmetry of the production of top-quark and antiquark pairs in proton-antiproton collisions at center-of-mass energy $\sqrt{s}=1.96\mathrm{TeV}$ using the full data set collected by the Collider Detector at Fermilab (CDF) in Tevatron Run II corresponding to an integrated luminosity of $9.1{\mathrm{fb}}^{-1}$. The asymmetry is characterized by the rapidity difference between top quarks and antiquarks ($\mathrm{\Delta }y$) and measured in the final state with two charged leptons (electrons and muons). The inclusive asymmetry, corrected to the entire phase space at parton level, is measured to be $A_{\mathrm{FB}}^{t\overline{t}}=0.12\pm 0.13$, consistent with the expectations from the standard model (SM) and previous CDF results in the final state with a single charged lepton. The combination of the CDF measurements of the inclusive $A_{\mathrm{FB}}^{t\overline{t}}$ in both final states yields $A_{\mathrm{FB}}^{t\overline{t}}=0.160\pm 0.045$, which is consistent with the SM predictions. We also measure the differential asymmetry as a function of $\mathrm{\Delta }y$. A linear fit to $A_{\mathrm{FB}}^{t\overline{t}}(|\mathrm{\Delta }y|)$, assuming zero asymmetry at $\mathrm{\Delta }y=0$, yields a slope of $\alpha =0.14\pm 0.15$, consistent with the SM prediction and the previous CDF determination in the final state with a single charged lepton. The combined slope of $A_{\mathrm{FB}}^{t\overline{t}}(|\mathrm{\Delta }y|)$ in the two final states is $\alpha =0.227\pm 0.057$, which is $2.0\sigma$ larger than the SM prediction.

In this paper, we study the influence of an external magnetic field in holographic QCD models where the backreaction is modeled via an appropriate choice of the background metric. We add a phenomenological soft wall dilaton to incorporate better IR behavior (confinement). Elaborating on previous studies conducted by [K. A. Mamo, J. High Energy Phys. 05 (2015) 121.], we first discuss the Hawking-Page transition, the dual of the deconfinement transition, as a function of the magnetic field. We confirm that the critical deconfinement temperature can drop with the magnetic field. Secondly, we study the quark condensate holographically as a function of the applied magnetic field and demonstrate that this model does not exhibit inverse magnetic catalysis at the level of the chiral transition. The quest for a holographic QCD model that qualitatively describes the inverse magnetic catalysis at finite temperature is thus still open. Throughout this work, we pay special attention to the different holographic parameters and we attempt to fix them by making the link to genuine QCD as close as possible. This leads to several unanticipated and so far overlooked complications (such as the relevance of an additional length scale ${\ell }_c$ in the confined geometry) that we discuss in detail.

The vacuum state of a relativistic quantum field contains entanglement between regions separated by spacelike intervals. Such spatial entanglement can be revealed using an operational method introduced in [M. Rodriguez-Vazquez, M. del Rey, H. Westman, and J. Leon, Ann. Phys. (N.Y.) 351, 112 (2014), E. G. Brown, M. del Rey, H. Westman, J. Leon, and A. Dragan, Phys. Rev. D 91, 016005 (2015)]. In this approach, a cavity is instantaneously divided into halves by an introduction of an extra perfect mirror. Causal separation of the two regions of the cavity reveals nonlocal spatial correlations present in the field, which can be quantified by measuring particles generated in the process. We use this method to study spatial entanglement properties of nonvacuum Gaussian field states. In particular, we show how to enhance the amount of harvested spatial entanglement by an appropriate choice of the initial state of the field in the cavity. We find a counterintuitive influence of the initial entanglement between cavity modes on the spatial entanglement which is revealed by dividing the cavity in half.

In this paper, an extension of the classification of flipped $SU(5)$ heterotic-string vacua from Faraggi, Rizos and Sonmez [Nucl. Phys. B886, 202 (2014)] with a variation of the $SO(10)$ breaking $\alpha$ basis vector is presented. A statistical sampling in the space of $2^{45}$ flipped $SU(5)$ vacua is explored, where ${10}^{11}$ distinct GGSO projection configurations are scanned in comparison to the ${10}^{12}$ GGSO distinct coefficients scanned in the space of $2^{44}$ vacua in Faraggi, Rizos and Sonmez. A JAVA code, akin to the one used for the classification in Faraggi, Rizos and Sonmez, was implemented to explore these. Results presented here indicate that no three-generation exophobic vacua exist, which was also found to be the case in Faraggi, Rizos and Sonmez as all odd generations were projected out. This paper will also study the details on the comparison between the two classifications achieved and reflect on the future directions in the quest for finding three-generation exophobic flipped $SU(5)$ heterotic-string models.

We construct the graviton two-point function for a two-parameter family of linear covariant gauges in $n$-dimensional de Sitter space. The construction is performed via the mode-sum method in the Bunch-Davies vacuum in the Poincaré patch, and a Fierz-Pauli mass term is introduced to regularize the infrared (IR) divergences. The resulting two-point function is de Sitter invariant and free of IR divergences in the massless limit (for a certain range of parameters), although analytic continuation with respect to the mass for the pure-gauge sector of the two-point function is necessary for this result. This general result agrees with the propagator obtained by analytic continuation from the sphere [Phys. Rev. D 34, 3670 (1986); Classical Quantum Gravity 18, 4317 (2001)]. However, if one starts with strictly zero mass theory, the IR divergences are absent only for a specific value of one of the two parameters, with the other parameter left generic. These findings agree with recent calculations in the Landau (exact) gauge [J. Math. Phys. 53, 122502 (2012)], where IR divergences do appear in the spin-two (tensor) part of the two-point function. However, we find the strength (including the sign) of the IR divergence to be different from the one found in this reference.