We present the general expression, in terms of structure functions, of the cross section for the production of two hadrons in semi-inclusive deep inelastic scattering. We analyze this process including full transverse-momentum dependence up to subleading twist and check, where possible, the consistency with existing literature.

The case of heavy quark propagation in dense extended matter is studied in the multiple scattering formalism of the higher twist energy loss scheme. We consider the case of deep inelastic scattering off a large nucleus. The hard lepton scatters off a heavy quark fluctuation within one of the nucleons. This heavy quark then propagates through the dense medium, multiply scattering off the gluon field of the remaining nucleons in its path. We consider the fictitious process where a heavy quark propagates through the nucleus without radiation. Invoking soft-collinear effective theory power counting arguments, we consider the case of a “semihard” heavy quark where the mass is of the order of the outgoing momentum and larger than the transverse momentum imparted per unit length due to scattering. In this limit, it is found that longitudinal momentum exchanges (quantified by the transport coefficient $\widehat{e}$) have a comparable effect on the off-shellness of the propagating quark, as the transverse momentum exchanges (quantified by $\widehat{q}$) which constitute the leading cause of off-shellness for propagating light quarks or gluons. Consequences of this new hierarchy for the propagation of the heavy quark in dense matter are discussed.

The existence of the inflationary era in the early Universe seems to be strongly supported by recent CMB observations. However, only a few realistic inflation scenarios which have close relation to particle physics seem to have been known unfortunately. The radiative neutrino mass model with inert doublet dark matter is a promising model for the present experimental issues which cannot be explained within the standard model. In order to make the model include inflation, we extend it by a complex scalar field with a specific potential. This scalar could be closely related to the neutrino mass generation at a TeV scale as well as inflation. We show that the inflation favored by the CMB observations could be realized even if inflaton takes sub-Planck values during inflation.

Using a sample of $2.25\times 10^8$ $J/\psi$ events collected with the BESIII detector at the BEPCII collider, we search for the $J/\psi$ semileptonic weak decay $J/\psi \to D_s^{-}{e}^{+}{\nu }_e+\mathrm{c}.\mathrm{c}.$ with a much higher sensitivity than previous searches. We also perform the first search for $J/\psi \to D_s^{*-}{e}^{+}{\nu }_e+\mathrm{c}.\mathrm{c}.$ No significant excess of a signal above background is observed in either channel. At the 90% confidence level, the upper limits are determined to be $\mathcal{B}(J/\psi \to D_s^{-}{e}^{+}{\nu }_e+\mathrm{c}.\mathrm{c}.)<1.3\times 10^{-6}$ and $\mathcal{B}(J/\psi \to {D_s^{*}}^{-}{e}^{+}{\nu }_e+\mathrm{c}.\mathrm{c}.)<1.8\times 10^{-6}$, respectively. Both are consistent with Standard Model predictions.

Searches are presented for heavy scalar ($H$) and pseudoscalar ($A$) Higgs bosons posited in the two doublet model (2HDM) extensions of the standard model (SM). These searches are based on a data sample of $pp$ collisions collected with the CMS experiment at the LHC at a center-of-mass energy of $\sqrt{s}=8\mathrm{TeV}$ and corresponding to an integrated luminosity of $19.5{\mathrm{fb}}^{-1}$. The decays $H\to hh$ and $A\to Zh$, where $h$ denotes an SM-like Higgs boson, lead to events with three or more isolated charged leptons or with a photon pair accompanied by one or more isolated leptons. The search results are presented in terms of the $H$ and $A$ production cross sections times branching fractions and are further interpreted in terms of 2HDM parameters. We place 95% C.L. cross section upper limits of approximately 7 pb on $\sigma \mathcal{B}$ for $H\to hh$ and 2 pb for $A\to Zh$. Also presented are the results of a search for the rare decay of the top quark that results in a charm quark and an SM Higgs boson, $t\to ch$, the existence of which would indicate a nonzero flavor-changing Yukawa coupling of the top quark to the Higgs boson. We place a 95% C.L. upper limit of 0.56% on $\mathcal{B}(t\to ch)$.

We report on a search in $e^{+}{e}^{-}$ annihilations for new ${\pi }^0$-like particles produced in association with a $\tau$-lepton pair. These objects, with a similar mass and similar decay modes to ${\pi }^0$ mesons, could provide an explanation for the non-asymptotic behavior of the pion-photon transition form factor observed by the BABAR Collaboration. No significant signal is observed, and limits on the production cross section at the level of 73 fb or 370 fb, depending on the model parameters, are determined at 90% confidence level. These upper limits lie below the cross section values needed to explain the BABAR form factor data.

The changes in the cosmic microwave background (CMB) spectrum seen as an increase of temperature due to a strong magnetic field are determined and their influence on the polarization of the radiation is exhibited. The effect is due to the coupling of the CMB photons to the magnetic field in the QED vacuum via the interaction with virtual pairs. In spite of the fact that the distortion of the CMB spectrum for magnetic fields that exist in the vicinity of magnetars is quite large, this effect is very difficult to detect at present because the required angular resolutions is not yet available.

We extend our previous investigation of the two-loop $\mathrm{\Phi }$-derivable approximation to the case of a finite chemical potential $\mu$ and discuss Bose-Einstein condensation in the case of a charged scalar field with $O(2)$ symmetry. We show that the approximation is renormalizable by means of counterterms which are independent of both the temperature and the chemical potential. We point out the presence of an additional skew contribution to the propagator as compared to the $\mu =0$ case, which comes with its own gap equation (except at Hartree level). We solve this equation together with the field equation, and the usual longitudinal and transversal gap equations to find that the transition is second order, in agreement with recent lattice results to which we compare. We also discuss a general criterion an approximation should obey for the so-called Silver Blaze property to hold, and we show that any $\mathrm{\Phi }$-derivable approximation at finite temperature and density obeys this criterion if one chooses an UV regularization that does not cut off the Matsubara sums.

Mensky has suggested to account for “continuous measurement” by attaching to a path integral a weight function centered around the classical path to which the integral assigns a probability amplitude. We show that in fact this weight function does not have to be viewed as an additional ingredient put in by hand. It can be derived instead from the conventional path integral if the infinitesimal term $\mathrm{i}\epsilon$ in the propagator is made finite; the “classical trajectory” is proportional to the current.

We investigate the descriptions for the observables of inflationary models, in particular, the spectral index of curvature perturbations, the tensor-to-scalar ratio, and the running of the spectral index, in the framework of perfect fluid models and $F(R)$ gravity theories through the reconstruction methods. Furthermore, the perfect fluid and $F(R)$ gravity descriptions of inflation are compared with the recent cosmological observations such as the Planck satellite and BICEP2 experiment. It is demonstrated with explicit examples that perfect fluid may lead to the inflationary universe consistent with the Planck data. It is also shown that several $F(R)$ gravity models, especially, a power-law model gives the best fit values compatible with the spectral index and tensor-to-scalar ratio within the allowed ranges suggested by the Planck and BICEP2 results.

There is a considerable amount of evidence to suggest that the field equations of gravity have the same status as, say, the equations describing an emergent phenomenon like elasticity. In fact, it is possible to derive the field equations from a thermodynamic variational principle in which a set of normalized vector fields are varied rather than the metric. We show that this variational principle can arise as a low-energy [$L_P=(G\hslash /c^3{)}^{1/2}\to 0$] relic of a plausible nonperturbative effect of quantum gravity, viz. the existence of a zero-point length in the spacetime. Our result is nonperturbative in the following sense: If we modify the geodesic distance in a spacetime by introducing a zero-point length, to incorporate some effects of quantum gravity, and take the limit $L_P\to 0$ of the Ricci scalar of the modified metric, we end up getting a nontrivial, leading order ($L_P$-independent) term. This term is identical to the expression for entropy density of spacetime used previously in the emergent gravity approach. This reconfirms the idea that the microscopic degrees of freedom of the spacetime, when properly described in the full theory, could lead to an effective description of geometry in terms of a thermodynamic variational principle. This is conceptually similar to the emergence of thermodynamics from the mechanics of, say, molecules. The approach also has important implications for the cosmological constant which are briefly discussed.

We have investigated the wave dynamics of a vector field perturbation coupling to the Einstein tensor in the four-dimensional Reissner-Nordström black hole spacetime. Our results show that besides the dependence on the coupling between the vector field and Einstein tensor, the wave dynamic equation of the vector field perturbation strongly depends on the parity of the perturbation itself, which is quite different from that of the usual vector field perturbation without the coupling in the four-dimensional spacetime. Moreover, we also find that the vector field perturbation with odd parity grows with an exponential rate if the coupling strength is stronger than a certain critical value. However, the vector field perturbation with even parity always decays in the Reissner-Nordström black hole spacetime.

We analyze the frequency shift of photons propagating on an asymptotically flat spacetime describing a collapsing, spherical dust cloud. We focus on the case where the interaction of the photons with the matter can be neglected. Under fairly general assumptions on the initial data characterizing the collapse, we show that photons with zero angular momentum which travel from past to future null infinity, crossing the collapsing cloud through its center, are always redshifted with respect to stationary observers. We compute this redshift as a function of proper time of a distant stationary observer and discuss its dependency on the mass distribution of the cloud. Possible implications of this redshift effect for weak cosmic censorship and light propagation in cosmological spacetimes are also briefly discussed.

The oscillation of the cosmic microwave background (CMB) photons into axions can cause CMB spectral distortion in the presence of a large-scale magnetic field. With the COBE collaboration limit on the $\mu$ parameter and a homogeneous magnetic field with strength $B\lesssim 3.2\mathrm{nG}$ at the horizon scale, a stronger lower limit on the axion mass in comparison with the limit of the ADMX experiment is found to be $4.8\times 10^{-5}\mathrm{eV}\lesssim m_a$ for the Kim-Shifman-Vainshtein-Zakharov (KSVZ) axion model. On the other hand, using the experimental limit on the axion mass $3.5\times 10^{-6}\mathrm{eV}\lesssim m_a$ from the ADMX experiment together with the COBE bound on $\mu$, $B\lesssim 53\mathrm{nG}$ is found for the KSVZ axion model and $B\lesssim 141\mathrm{nG}$ for the Dine-Fischler-Sdrenicki-Zhitnitsky (DFSZ) axion model, for a homogeneous magnetic field with coherence length at the present epoch ${\lambda }_B\sim 1.3\mathrm{Mpc}$. Limits on $B$ and $m_a$ for PIXIE/PRISM expected sensitivity on $\mu$ are derived. If CMB $\mu$ distortion would be detected by the future space missions PIXIE/PRISM and assuming that the strength of the large-scale magnetic field is close to its canonical value, $B\sim 1–3\mathrm{nG}$, axions in the mass range $2–3\mu \mathrm{eV}$ would be potential candidates of CMB $\mu$ distortion.

A study of proton-proton collisions at very high energy has revealed a “black disk,” whose radius grows with the logarithm of the center-of-mass energy, surrounded by an edge of approximately constant width 1 fm. We interpret this behavior as the maximum length of a QCD string connecting the color triplet and antitriplet components of the proton, and we propose further tests of this explanation.

The basic principle of naturalness has driven the majority of the LHC program, but so far all searches for new physics beyond the SM have come up empty. On the other hand, existing measurements of SM processes contain interesting anomalies, which allow for the possibility of new physics with mass scales very close to the electroweak scale. In this paper we show that SUSY could have stops with masses $\mathcal{O}(200)\mathrm{GeV}$ based on an anomaly in the $W^{+}{W}^{-}$ cross section, measured by both ATLAS and CMS at 7 and 8 TeV. In particular we show that there are several different classes of stop-driven scenarios that not only evade all direct searches, but also improve the agreement with the data in the SM measurement of the $W^{+}{W}^{-}$ cross section.

We investigate superfluidity, and the mechanism for creation of quantized vortices, in the relativistic regime. The general framework is a nonlinear Klein-Gordon equation in curved spacetime for a complex scalar field, whose phase dynamics gives rise to superfluidity. The mechanisms discussed are local inertial forces (Coriolis and centrifugal), and current-current interaction with an external source. The primary application is to cosmology, but we also discuss the reduction to the nonrelativistic nonlinear Schrödinger equation, which is widely used in describing superfluidity and vorticity in liquid helium and cold-trapped atomic gases.

Finsler geometry is a natural generalization of pseudo-Riemannian geometry. It can be motivated e.g. by a modified version of the Ehlers-Pirani-Schild axiomatic approach to space-time theory. Also, some scenarios of quantum gravity suggest a modified dispersion relation which could be phrased in terms of Finsler geometry. On a Finslerian space-time, the universality of free fall is still satisfied but local Lorentz invariance is violated in a way not covered by standard Lorentz invariance violation schemes. In this paper we consider a Finslerian modification of Maxwell’s equations. The corrections to the Coulomb potential and to the hydrogen energy levels are computed. We find that the Finsler metric corrections yield a splitting of the energy levels. Experimental data provide bounds for the Finsler parameters.

The possibility of dark matter being a dissipative component represents an option for the standard view where cold dark matter (CDM) particles behave on large scales as an ideal fluid. By including a physical mechanism in the dark matter description like viscosity, we construct a more realistic model for the Universe. Also, the known small scale pathologies of the standard CDM model either disappear or become less severe. We study clustering properties of a $\mathrm{\Lambda }\mathrm{CDM}$-like model in which dark matter is described as a bulk viscous fluid. The linear power spectrum, the nonlinear spherical "top hat" collapse, and the mass functions are presented. We use the analysis with such structure formation tools in order to place an upper bound on the magnitude of the dark matter’s viscosity.

There are two disjointed problems in cosmology within general relativity (GR), which can be addressed simultaneously by studying the nature of geodesics around $t\to 0$, where $t$ is the physical time. One is related to the past geodesic completeness of the inflationary trajectory due to the presence of a cosmological singularity, and the other one is related to the homogeneity condition required to inflate a local space-time patch of the Universe. We will show that both the problems have a common origin, arising from how the causal structure of null and timelike geodesics are structured within GR. In particular, we will show how a nonlocal extension of GR can address both problems, while satisfying the null energy condition for the matter sources.