Most inflationary models predict primordial perturbations to be statistically isotropic and homogeneous. Cosmic microwave background (CMB) observations, however, indicate a possible departure from statistical isotropy in the form of a dipolar power modulation at large angular scales. Alternative models of inflation, beyond the simplest single-field slow-roll models, can generate a small power asymmetry, consistent with these observations. Observations of clustering of quasars show, however, agreement with statistical isotropy at much smaller angular scales. Here, we propose to use off-diagonal components of the angular power spectrum of the 21-cm fluctuations during the dark ages to test this power asymmetry. We forecast results for the planned SKA radio array, a future radio array, and the cosmic-variance-limited case as a theoretical proof of principle. Our results show that the 21-cm line power spectrum will enable access to information at very small scales and at different redshift slices, thus improving upon the current CMB constraints by $\sim 2$ orders of magnitude for a dipolar asymmetry and by $\sim 1–3$ orders of magnitude for a quadrupolar asymmetry case.

We perform a phase space analysis of a generalized modified gravity theory with nonminimally coupling between geometry and matter. We apply the dynamical system approach to this generalized model and find that in the cosmological context, different choices of Lagrangian density will apparently result in different phases of the Universe. By carefully choosing the variables, we prove that there is an attractor solution to describe the late time accelerating universe when the modified gravity is chosen in a simple power-law form of the curvature scalar. We further examine the temperature evolution based on the thermodynamic understanding of the model. Confronting the model with supernova type Ia data sets, we find that the nonminimally coupled theory of gravity is a viable model to describe the late time Universe acceleration.

General relativity is supported by great experimental evidence. Yet there is a lot of interest in precisely setting its limits with on going and future experiments. A question to answer is about the validity of the strong equivalence principle. Ground experiments and lunar laser ranging have provided the best upper limit on the Nordtvedt parameter $\sigma [\eta ]=4.4\times {10}^{-4}$. With the future planetary mission BepiColombo, this parameter will be further improved by at least an order of magnitude. In this paper we envisage yet another possible testing environment with spacecraft ranging towards the nearby Sun-Earth collinear Lagrangian points. Neglecting errors in planetary masses and ephemerides, we forecast $\sigma [\eta ]=6.4(2.0)\times {10}^{-4}$ (5 yr integration time) via ranging towards $L_1$ in a realistic (optimistic) scenario depending on current (future) range capabilities and knowledge of the Earth’s ephemerides. A combined measurement, $L_1+L_2$, gives instead $4.8(1.7)\times {10}^{-4}$. In the optimistic scenario a single measurement of one year would be enough to reach $\approx 3\times {10}^{-4}$. All figures are comparable with lunar laser ranging, but worse than BepiColombo. Performances could be much improved if data were integrated over time and over the number of satellites flying around either of the two Lagrangian points. We point out that some systematics (gravitational perturbations of other planets or figure effects) are much more in control compared to other experiments. We do not advocate a specific mission to constrain the strong equivalence principle, but we do suggest analyzing ranging data of present and future spacecrafts flying around $L_1/L_2$ (one key mission is, for instance, LISA Pathfinder). This spacecraft ranging would be a new and complementary probe to constrain the strong equivalence principle in space.

In this article, we revisit the coherent gravitational wave search problem of compact binary coalescences with multidetector network consisting of advanced interferometers like LIGO-Virgo. Based on the loss of the optimal multidetector signal-to-noise ratio (SNR), we construct a hybrid statistic as a best of maximum-likelihood-ratio (MLR) statistic tuned for face-on and face-off binaries. The statistical properties of the hybrid statistic is studied. The performance of this hybrid statistic is compared with that of the coherent MLR statistic for generic inclination angles. Owing to the single synthetic data stream, the hybrid statistic gives few false alarms compared to the multidetector MLR statistic and small fractional loss in the optimum SNR for a large range of binary inclinations. We demonstrate that, for a LIGO-Virgo network and binary inclination $\epsilon <70°$ and $\epsilon >110°$, the hybrid statistic captures more than 98% of the network optimum matched filter SNR with a low false alarm rate. The Monte Carlo exercise with two distributions of incoming inclination angles—namely, $U[\cos \epsilon ]$ and a more realistic distribution proposed by B. F. Schutz [Classical Quantum Gravity 28, 125023 (2011)]—are performed with the hybrid statistic and give approximately 5% and 7% higher detection probabilities, respectively, compared to the two stream multidetector MLR statistic for a fixed false alarm probability of $10^{-5}$.

Recent results from the experimental collaborations at LHC give hints of a resonance in the diphoton channel at an invariant mass of 750 GeV. We show that such a scalar resonance would be possible in an $U(1)$ extension of the standard model where the extended symmetry is hidden and yet to be discovered. We explore the possibilities of accommodating this excess by introducing a minimal extension to the matter content and highlight the parameter space that can accommodate the observed diphoton resonance in the model. The model also predicts new interesting signals that may be observed at the current LHC run.

In this paper, we discuss the minimal supersymmetric standard model (MSSM) extended with one vectorlike lepton doublet $L-\overline{L}$ and one right-handed neutrino $N$. The neutral vecotorlike sneutrino can be a candidate of dark matter. To avoid the interaction with the nucleons by exchanging a $Z$ boson, the mass splitting between the real part and the imaginary part of the sneutrino field is needed. Compared with the MSSM sneutrino dark matter, the mass splitting between the vectorlike sneutrino field can be more naturally acquired without large A terms and constraints on the neutralino masses. We have also calculated the relic density and the elastic scattering cross sections with the nucleons in the cases that the dark matter particles coannihilate with or without the MSSM slepton doublets. The elastic scattering cross sections with the nucleons are well below the LUX bounds. In the case that the dark matter coannihilates with all the MSSM slepton doublets, the mass of the dark matter can be as light as 370 GeV.

In this work, we present limits on natural supersymmetry scenarios based on searches in data taken during run 1 of the LHC. We consider a set of 22 000 model points in a six dimensional parameter space. These scenarios are minimal in the sense of only keeping those superparticles relatively light that are required to cancel the leading quadratically divergent quantum corrections (from the top and QCD sector) to the Higgs mass in the Standard Model. The resulting mass spectra feature Higgsinos as the lightest supersymmetric particle, as well as relatively light third generation $SU(2)$ doublet squarks and $SU(2)$ singlet stops and gluinos while assuming a Standard-Model-like Higgs boson. All remaining supersymmetric particles and Higgs bosons are assumed to be decoupled. We check each parameter set against a large number of LHC searches as implemented in the public code CheckMATE. These searches show a considerable degree of complementarity, i.e., in general, many searches have to be considered in order to check whether a given scenario is allowed. We delineate allowed and excluded regions in parameter space. For example, we find that all scenarios where either $m_{{\tilde{t}}_1}<230\mathrm{GeV}$ or $m_{\tilde{g}}<440\mathrm{GeV}$ are clearly excluded, while all model points where $m_{{\tilde{t}}_1}>660\mathrm{GeV}$ and $m_{\tilde{g}}>1180\mathrm{GeV}$ remain allowed.

Inspired by a significance of $2.4\sigma$ for the $h\to \mu \tau$ decay observed by the CMS experiment at $\sqrt{s}=8\mathrm{TeV}$, we investigate the Higgs lepton-flavor-violating effects in a generic two-Higgs-doublet model (THDM), where the lepton-flavor-changing neutral currents are induced at the tree level and arise from the Yukawa sector. We revisit the constraints for generic THDM by considering theoretical requirements, precision measurements of $\delta \rho$ and oblique parameters $S$, $T$, and $U$, and Higgs measurements. The bounds from Higgs data play the major limits. With parameter values that simultaneously satisfy the Higgs bounds and the CMS excess of the Higgs coupling to $\mu -\tau$, we find that the tree-level $\tau \to 3\mu$ and the loop-induced $\tau \to \mu \gamma$ decays are consistent with current experimental upper limits; the discrepancy in muon $g-2$ between experimental results and standard model predictions can be resolved, and an interesting relation between muon $g-2$ and the branching ratio (BR) for $\mu \to e\gamma$ is found. The generic THDM results show that the order of magnitude of the ratio $\mathrm{BR}(h\to e\tau )/\mathrm{BR}(h\to \mu \tau )$ is smaller than $10^{-4}$. Additionally, we also study the rare decay $Z\to \mu \tau$ and get $\mathrm{BR}(Z\to \mu \tau )<10^{-6}$.

We study rare four-body decays of the $Z$-boson involving at least one neutrino and one charged lepton. Large destructive interferences make these decays very sensitive to the $Z$ couplings to neutrinos. As the identified charged leptons can determine the neutrino flavors, these decays probe the universality of the $Z$ couplings to neutrinos. The rare four-body processes could be accurately measured at future lepton colliders, leading to percent level precision.

We consider extensions of the Standard Model in which the hierarchy between the unification and the Fermi scale emerges radiatively. Within the Pati-Salam framework, we show that it is possible to construct a viable model where the Higgs is an elementary pseudo-Goldstone boson, and the correct hierarchy is generated.

The mass, decay constant, and width of a hypothetical charmed partner $X_c$ of the newly observed exotic $X_b(5568)$ state are calculated using the technique of the QCD sum rule method. The $X_c=[su][\overline{c}\overline{d}]$ state with $J^P=0^{+}$ is described, employing two types of the diquark-antidiquark interpolating currents. The evaluation of the mass $m_{X_c}$ and decay constant $f_{X_c}$ is carried out utilizing the two-point sum rule method by including vacuum condensates up to eight dimensions. The widths of the decay channels $X_c\to D_s^{-}{\pi }^{+}$ and $X_c\to D^0{K}^0$ are also found. To this end, the strong couplings $g_{X_c{D}_s\pi }$ and $g_{X_{c}DK}$ are computed by means of QCD sum rules on the light-cone and soft-meson approximation.

The CDEX-1 experiment conducted a search of low-mass ($<10\mathrm{GeV}/c^2$) weakly interacting massive particles dark matter at the China Jinping Underground Laboratory using a p-type point-contact germanium detector with a fiducial mass of 915 g at a physics analysis threshold of 475 eVee. We report the hardware setup, detector characterization, data acquisition, and analysis procedures of this experiment. No excess of unidentified events is observed after the subtraction of the known background. Using 335.6 kg-days of data, exclusion constraints on the weakly interacting massive particle-nucleon spin-independent and spin-dependent couplings are derived.

In the presence of Lorentz violation, the Cerenkov-like process $\gamma \to \gamma +{\pi }^0$ may become allowed for sufficiently energetic photons. Photons above the threshold would lose energy rapidly through pion emission. The fact that propagating photons with energies of up to 80 TeV survive to be observed on Earth allows us to place a one-sided constraint on an isotropic Lorentz-violating parameter at the $7\times {10}^{-13}$ level; this is more than an order of magnitude better than the best previous result.

Motivated by recent experimental efforts, we study a black hole analog induced by the propagation of a strong laser pulse in a nonlinear dielectric medium. Based on the Hopfield model (one pair of Sellmeier coefficients), we perform an analytic and fully relativistic microscopic derivation of the analog of Hawking radiation in this setup. The Hawking temperature is determined by the analog of the surface gravity (as expected), but we also find a frequency-dependent gray-body factor (i.e., a nonthermal spectrum at infinity) due to the breaking of conformal invariance in this setup.

Starting from a phenomenologically successful, numerical solution of the Dyson-Schwinger equation that governs the quark propagator, we reconstruct in detail the interaction kernel that has to enter the instantaneous approximation to the Bethe-Salpeter equation to allow us to describe the lightest pseudoscalar mesons as quark-antiquark bound states exhibiting the (almost) masslessness necessary for them to be interpretable as the (pseudo) Goldstone bosons related to the spontaneous chiral symmetry breaking of quantum chromodynamics.

The mass spectra of the $[\mathbf{56},2^{+}]$ and $[\mathbf{70},\ell +]$ multiplets, both belonging to the $N=2$ band, are reviewed in the $1/N_c$ expansion method. Previous studies, separately made for each multiplet, are presently updated to the 2014 Particle Data Group. The mass formula, including corrections up to $\mathcal{O}(1/N_c)$ and first order in SU(3) flavor symmetry breaking, has the same independent operator basis in both cases. A special emphasis is made on the role of the SU(3) symmetry breaking operators $B_i$ $(i=1,2,3)$. This can allow for multiplet assignment of $\mathrm{\Lambda }$ and $\mathrm{\Sigma }$ hyperons, which generally is quite difficult to make. Tentative assignments of hyperons with two- and one-star resonances are made to the $[\mathbf{70},\ell +]$ multiplet. Another important aim is to find out whether or not a common value of the coefficient $c_1$ of the dominant operator in the mass formula can well fit the present data in both multiplets. A negative answer, which is here the case, implies distinct Regge trajectories for symmetric and mixed symmetric states.

We present a lattice calculation of the neutron and proton electric dipole moments (EDMs) with $N_f=2+1$ flavors of domain-wall fermions. The neutron and proton EDM form factors are extracted from three-point functions at the next-to-leading order in the $\theta$ vacuum of QCD. In this computation, we use pion masses of 0.33 and 0.42 GeV and $2.7{\mathrm{fm}}^3$ lattices with Iwasaki gauge action, and a 0.17 GeV pion and a $4.6{\mathrm{fm}}^3$ lattice with I-DSDR gauge action, all generated by the RBC and UKQCD collaborations. The all-mode averaging technique enables an efficient and high statistics calculation. Chiral behavior of lattice EDMs is discussed in the context of baryon chiral perturbation theory. In addition, we also show numerical evidence on the relationship of three- and two-point correlation functions with the local topological charge distribution.

We construct the free field representation of irregular vertex operators of arbitrary rank which generates simultaneous eigenstates of positive modes of Virasoro and W symmetry generators. The irregular vertex operators turn out to be the exponentials of combinations of derivatives of Liouville or Toda fields, creating irregular coherent states. We compute examples of correlation functions of these operators and study their operator algebra.

Scale-invariant theories are often used to address the hierarchy problem. However the regularization of their quantum corrections introduces a dimensionful coupling (dimensional regularization) or scale (Pauli-Villars, etc) which breaks this symmetry explicitly. We show how to avoid this problem and study the implications of a manifestly scale-invariant regularization in (classical) scale-invariant theories. We use a dilaton-dependent subtraction function $\mu (\sigma )$ which, after spontaneous breaking of the scale symmetry, generates the usual dimensional regularization subtraction scale $\mu (⟨\sigma ⟩)$. One consequence is that “evanescent” interactions generated by scale invariance of the action in $d=4-2\epsilon$ (but vanishing in $d=4$) give rise to new, finite quantum corrections. We find a (finite) correction $\mathrm{\Delta }U(\varphi ,\sigma )$ to the one-loop scalar potential for $\varphi$ and $\sigma$, beyond the Coleman-Weinberg term. $\mathrm{\Delta }U$ is due to an evanescent correction ($\propto \epsilon$) to the field-dependent masses (of the states in the loop) which multiplies the pole ($\propto 1/\epsilon$) of the momentum integral to give a finite quantum result. $\mathrm{\Delta }U$ contains a nonpolynomial operator $\sim {\varphi }^6/{\sigma }^2$ of known coefficient and is independent of the subtraction dimensionless parameter. A more general $\mu (\varphi ,\sigma )$ is ruled out since, in their classical decoupling limit, the visible sector (of the Higgs $\varphi$) and hidden sector (dilaton $\sigma$) still interact at the quantum level; thus, the subtraction function must depend on the dilaton only, $\mu \sim \sigma$. The method is useful in models where preserving scale symmetry at quantum level is important.

The electric permittivities and magnetic permeabilities for a relativistic electron gas are calculated from quantum electrodynamics at finite temperature and density as functions of temperature, chemical potential, frequency, and wave vector. The polarization and the magnetization depend linearly on both electric and magnetic fields, and are the sum of a zero-temperature and zero-density vacuum part with a temperature- and chemical-potential-dependent medium part. Analytic calculations lead to generalized expressions that depend on three scalar functions. In the nonrelativistic limit, results reproduce the Lindhard formula. In the relativistic case, and in the long wavelength limit, we obtain the following: (i) for $\omega =0$, generalized susceptibilities that reduce to known nonrelativistic limits; (ii) for $\omega \ne 0$, Drude-type responses at zero temperature. The latter implies that both the electric permittivity $\epsilon$ and the magnetic permeability $\mu$ may be simultaneously negative, a behavior characteristic of metamaterials. This unambiguously indicates that the relativistic electron gas is one of nature’s candidates for the realization of a negative index of refraction system. Moreover, Maxwell’s equations in the medium yield the dispersion relation and the index of refraction of the electron gas. Present results should be relevant for plasma physics, astrophysical observations, synchrotrons, and other environments with fast-moving electrons.