If the lighter top squark has no kinematically allowed two-body decays that conserve flavor, then it will live long enough to form hadronic bound states. The observation of the diphoton decays of stoponium could then provide a uniquely precise measurement of the top squark mass. In this paper, we calculate the cross section for the production of stoponium in a hadron collider at next-to-leading order (NLO) in QCD. We present numerical results for the cross section for production of stoponium at the LHC and study the dependence on beam energy, stoponium mass, and the renormalization and factorization scale. The cross-section is substantially increased by the NLO corrections, counteracting a corresponding decrease found earlier in the NLO diphoton branching ratio.

We update the constraints on the minimal model of dark matter, where a stable real scalar field is added to the standard model Lagrangian with a renormalizable coupling to the Higgs field. Once we fix the dark matter abundance, there are only two relevant model parameters, the mass of the scalar field and that of the Higgs boson. The recent data from the CDMS-II experiment have excluded a parameter region where the scalar field is light, such as less than about 50 GeV. In a large parameter region, the consistency of the model can be tested by the combination of future direct detection experiments and the LHC experiments.

Higher twist effects in the deeply inelastic scattering are studied. We start with a short review of the theoretical results on higher twists in QCD. Within the saturation model we perform a twist analysis of the nucleon structure functions $F_T$ and $F_L$ at small value of the Bjorken variable $x$. The parameters of the model are fitted to the HERA $F_2$ data, and we derive a prediction for the longitudinal structure function $F_L$. We conclude that for $F_L$ the higher twist corrections are sizable whereas for $F_2=F_T+F_L$ there is a nearly complete cancellation of twist-4 corrections in $F_T$ and $F_L$. We discuss a few consequences for future LHC measurements.

In this article, we investigate the contribution of the higher-twist Feynman diagrams to the large-$p_T$ inclusive single meson production cross section in photon-photon collisions and present the general formulas for the higher-twist differential cross sections in case of the running coupling and frozen coupling approaches. The structure of infrared renormalon singularities of the higher-twist subprocess cross section and the resummed expression (the Borel sum) for it are found. We compared the resummed higher-twist cross sections with the ones obtained in the framework of the frozen coupling approach and leading-twist cross section. We obtain, that ratio $R=({\Sigma }_{M^{+}}^{\mathrm{HT}}{)}^{\mathrm{res}}/({\Sigma }_{M^{+}}^{\mathrm{HT}}{)}^0$, for all values of the transverse momentum $p_T$ of the meson identically equivalent to ratio $r=({\Delta }_M^{\mathrm{HT}}{)}^{\mathrm{res}}/({\Delta }_M^{\mathrm{HT}}{)}^0$. It is shown that the resummed result depends on the choice of the meson wave functions used in calculation. Phenomenological effects of the obtained results are discussed.

The connection of Gribov’s confinement scenario in the Coulomb gauge with the center vortex picture of confinement is investigated. For this purpose we assume a vacuum wave functional that models the infrared properties of the theory and, in particular, shows strict confinement, i.e. an area law of the Wilson loop. We isolate the center vortex content of this wave functional by standard lattice methods and investigate their contributions to various static propagators of the Hamilton approach to Yang-Mills theory in the Coulomb gauge. We find that the infrared properties of these quantities, in particular, the infrared divergence of the ghost form factor, are dominated by center vortices.

We put robust upper limits on the average cosmological density ${\Omega }_s$ of cosmic strings based on the variability properties of a large homogeneous sample of Sloan Digital Sky Survey quasars. We search for an excess of characteristic variations of quasar brightness that are associated with string lensing and use the observed distribution of these variations to constrain the density of strings. The limits obtained do not invoke any clustering of strings. They apply to both open segments and closed loops of strings, usefully extend over a wide range of tensions ${10}^{-13}<G\mu /c^2<{10}^{-9}$, and reach down to the level of ${\Omega }_s=0.01$ and below. Further progress in this direction will depend on better understanding of quasar intrinsic variability rather than a mere increase in the volume of data.

We consider the observational effects of a deficit angle, $w$, in the topology of the solar system and in the “double pulsar” system PSR J0737-3039A/B. Using observations of the perihelion precession of Mercury, and the gravitational deflection of light due to the Sun, we constrain the magnitude of such a deficit angle in the solar system to be $2\pi (1-w)$, with $0\le (1-w)<{10}^{-9}$ at 95% confidence. We calculate the effects of a deficit angle on the periastron advance, geodetic precession rate and inclination angle of the double pulsar system and use the observational data to obtain the constraint $0\le (1-w)<2.4\times {10}^{-8}$ at 95% confidence. Although this result is weaker than the solar system bound, it is in a very different physical environment, where accumulating data is likely to lead to tighter constraints in the future.

We investigate the fermions of the standard model without a Higgs scalar. Instead, we consider a nonlocal four-quark interaction in the tensor channel which is characterized by a single dimensionless coupling $f$. Quantization leads to a consistent perturbative expansion for small $f$. The running of $f$ is asymptotically free and therefore induces a nonperturbative scale ${\Lambda }_{\mathrm{ch}}$, in analogy to the strong interactions. We argue that spontaneous electroweak symmetry breaking is triggered at a scale where $f$ grows large and find the top quark mass of the order of ${\Lambda }_{\mathrm{ch}}$. We also present a first estimate of the effective Yukawa coupling of a composite Higgs scalar to the top quark, as well as the associated mass ratio between the top quark and the $W$ boson.

Low-energy baryon-baryon interactions are calculated in a high-statistics lattice QCD study on a single ensemble of anisotropic-clover gauge-field configurations at a pion mass of $m_{\pi }\sim 390\mathrm{MeV}$, a spatial volume of $L^3\sim (2.5\mathrm{fm}{)}^3$, and a spatial lattice spacing of $b\sim 0.123\mathrm{fm}$. Lüscher’s method is used to extract nucleon-nucleon, hyperon-nucleon, and hyperon-hyperon scattering phase shifts at one momentum from the one- and two-baryon ground-state energies in the lattice volume. The isospin-$3/2$ $N\Sigma$ interactions are found to be highly spin dependent, and the interaction in the ${}^{3}S_1$ channel is found to be strong. In contrast, the $N\Lambda$ interactions are found to be spin independent, within the uncertainties of the calculation, consistent with the absence of one-pion exchange. The only channel for which a negative energy shift is found is $\Lambda \Lambda$, indicating that the $\Lambda \Lambda$ interaction is attractive, as anticipated from model-dependent discussions regarding the $H$ dibaryon. The nucleon-nucleon ($NN$) scattering lengths are found to be small, clearly indicating the absence of any fine-tuning in the $NN$ sector at this pion mass. This is consistent with our previous lattice QCD calculation of $NN$ interactions. The behavior of the signal-to-noise ratio in the baryon-baryon correlation functions, and in the ratio of correlation functions that yields the ground-state energy splitting is explored. In particular, focus is placed on the window of time slices for which the signal-to-noise ratio does not degrade exponentially, as this provides the opportunity to extract quantitative information about multibaryon systems.

We have measured the inclusive semileptonic branching fractions of $D^0$, $D^{+}$, and $D_s^{+}$ mesons. For these measurements, we have used the full CLEO-c open-charm data samples, $818{\mathrm{pb}}^{-1}$ at $E_{\mathrm{CM}}=3.774\mathrm{GeV}$, giving $D^0{\overline{D}}^0$ and $D^{+}{D}^{-}$ events, and $602{\mathrm{pb}}^{-1}$ at $E_{\mathrm{CM}}=4.170\mathrm{GeV}$, giving $D_s^{*\pm }{D}_s^{\mp }$ events. We obtain $\mathcal{B}(D^0\to X{e}^{+}{\nu }_e)=(6.46\pm 0.09\pm 0.11)\%$, $\mathcal{B}(D^{+}\to X{e}^{+}{\nu }_e)=(16.13\pm 0.10\pm 0.29)\%$, and $\mathcal{B}(D_s^{+}\to X{e}^{+}{\nu }_e)=(6.52\pm 0.39\pm 0.15)\%$, where the first uncertainties are statistical and the second are systematic. From these and lifetimes obtained elsewhere, we obtain the ratios of semileptonic decay widths $\Gamma (D^{+}\to X{e}^{+}{\nu }_e)/\Gamma (D^0\to X{e}^{+}{\nu }_e)=0.985\pm 0.015\pm 0.024$ and $\Gamma (D_s^{+}\to X{e}^{+}{\nu }_e)/\Gamma (D^0\to X{e}^{+}{\nu }_e)=0.828\pm 0.051\pm 0.025$. The ratio of $D^{+}$ and $D^0$ is consistent with the isospin symmetry prediction of unity, and the ratio of $D_s^{+}$ and $D^0$ differs from unity, as expected.

We describe hadronization events, using the AdS/CFT Correspondence, which display many of the qualitative features expected in QCD. In particular we study the motion of strings with separating end points in a back-reacted hard wall geometry. The solutions show the development of a linear QCD-like string. The end points oscillate in the absence of string breaking. We introduce string breaking by hand and evolve the new state forward in time to observe the separation of two string segments. A kink associated with this breaking evolves to the end points of the string inducing rho meson production. We explicitly compute the rho meson production at the end point.

We consider resonant Dirac leptogenesis in a geometry with three five-dimensional throats in the flat limit. The baryon asymmetry in the Universe is generated by resonant decays of heavy Kaluza-Klein scalars that are copies of the standard model Higgs. Discrete exchange symmetries between the throats are responsible for establishing two key features of the model. First, they ensure a near degeneracy of the scalar masses and thus a resonant decay of the scalars. This allows for Dirac leptogenesis at low energies close to the TeV scale. Second, the discrete symmetries connect the observed baryon asymmetry with the Yukawa couplings of the low-energy theory. As a consequence, we obtain correlations between the low-energy leptonic mixing parameters and the Dirac $CP$ phase that can be tested at future neutrino oscillation experiments such as neutrino factories.

For the first time, the process-independent parameter of double parton scattering ${\sigma }_{\mathrm{eff}}^{\exp }$ has been measured in the D0 experiment at three different resolution scales. If we interpret the measurement as a decrease of the effective cross section with a growth of the resolution scale, it can indicate the QCD evolution of double parton distributions.

Neutron stars are sensitive laboratories for testing general relativity, especially when considering deviations where velocities are relativistic and gravitational fields are strong. One such deviation is described by dynamical, Chern-Simons modified gravity, where the Einstein-Hilbert action is modified through the addition of the gravitational parity-violating Pontryagin density coupled to a field. This four-dimensional effective theory arises naturally both in perturbative and nonperturbative string theory, loop quantum gravity, and generic effective field theory expansions. We calculate here Chern-Simons modifications to the properties and gravitational fields of slowly spinning neutron stars. We find that the Chern-Simons correction affects only the gravitomagnetic sector of the metric to leading order, thus introducing modifications to the moment-of-inertia but not to the mass-radius relation. We show that an observational determination of the moment-of-inertia to an accuracy of 10%, as is expected from near-future observations of the double pulsar, will place a constraint on the Chern-Simons coupling constant of ${\xi }^{1/4}\lesssim 5\mathrm{km}$, which is at least three-orders of magnitude stronger than the previous strongest bound.

We develop the triangulated version of loop quantum cosmology, recently introduced in the literature. We focus on the dipole cosmology, where space is a three-sphere and the triangulation is formed by two tetrahedra. We show that the discrete fiducial connection has a simple and appealing geometrical interpretation and we correct the ansatz on the relation between the model variables and the Friedmann-Robertson-Walker scale factor. The modified ansatz leads to the convergence of the Hamiltonian constraint to the continuum one. We then ask which degrees of freedom are captured by this model. We show that the model is rich enough to describe the (anisotropic) Bianchi IX universe, and give the explicit relation between the Bianchi IX variables and the variables of the model. We discuss the possibility of using this path in order to define the quantization of the Bianchi IX universe. The model contains more degrees of freedom than Bianchi IX, and therefore captures some inhomogeneous degrees of freedom as well. Inhomogeneous degrees of freedom can be expanded in representations of the $SU(2)$ Bianchi IX isometry group, and the dipole model captures the lowest integer representation of these, connected to hyperspherical harmonic of angular momentum $j=1$.

Space-borne gravitational wave detectors, such as the proposed Laser Interferometer Space Antenna, are expected to observe black hole coalescences to high redshift and with large signal-to-noise ratios, rendering their gravitational waves ideal probes of fundamental physics. The promotion of Newton’s constant to a time function introduces modifications to the binary’s binding energy and the gravitational wave luminosity, leading to corrections in the chirping frequency. Such corrections propagate into the response function and, given a gravitational wave observation, they allow for constraints on the first time derivative of Newton’s constant at the time of merger. We find that space-borne detectors could indeed place interesting constraints on this quantity as a function of sky position and redshift, providing a constraint map over the entire range of redshifts where binary black hole mergers are expected to occur. A gravitational wave observation of an inspiral event with redshifted masses of ${10}^4–{10}^5$ solar masses for three years should be able to measure $\dot{G}/G$ at the time of merger to better than ${10}^{-11}{\mathrm{yr}}^{-1}$.

Dark matter annihilation is one of the leading explanations for recent cosmic $e^{\pm }$ excess observations by PAMELA, ATIC, FERMI-LAT, and H.E.S.S. Any dark matter annihilation model proposed to explain these data has to comply with the fact that PAMELA data show excesses only in $e^{\pm }$ spectrum but not in antiprotons. It is interesting to ask whether the annihilation mode into antiprotons is completely disallowed or just suppressed at low energies. Most proposed models have negligible antiprotons in all energy ranges. In this work we investigate the leptocentric $U(1{)}_{B-3L_i}$ dark matter model, and show that this model can explain the $e^{\pm }$ excesses with suppressed antiproton mode at low energies. But at higher energies there are sizable antiproton excesses. Near future data from PAMELA and AMS02 can provide crucial tests for this type of model. Cosmic $\gamma$ ray data can further rule out some of the models. We also show that this model has interesting neutrino signatures.

A long-range force acting only between nonbaryonic particles would be associated with a large violation of the weak equivalence principle. We explore cosmological consequences of this idea, which we label ReBEL (daRk Breaking Equivalence principLe). A high resolution hydrodynamical simulation of the distributions of baryons and dark matter confirms our previous findings that a ReBEL force of comparable strength to gravity on comoving scales of about $1{\mathrm{h}}^{-1}\mathrm{Mpc}$ causes voids between the concentrations of large galaxies to be more nearly empty, suppresses accretion of intergalactic matter onto galaxies at low redshift, and produces an early generation of dense dark-matter halos. A preliminary analysis indicates the ReBEL scenario is consistent with the one-dimensional power spectrum of the Lyman-Alpha forest and the three-dimensional galaxy autocorrelation function. Segregation of baryons and DM in galaxies and systems of galaxies is a strong prediction of ReBEL. ReBEL naturally correlates the baryon mass fraction in groups and clusters of galaxies with the system mass, in agreement with recent measurements.

We study the entire coupled evolution of the inflaton $\varphi (t)$ and the scale factor $a(t)$ for general initial conditions $\varphi (t_0)$ and $d\varphi (t_0)/dt$ at a given initial time $t_0$. The generic early Universe evolution has three stages: decelerated fast roll followed by inflationary fast roll and then inflationary slow roll (an attractor always reached for generic initial conditions). This evolution is valid for all regular inflaton potentials $v(\varphi )$. In addition, we find a special (extreme) slow-roll solution starting at $t=-\infty$ in which the fast-roll stages are absent. At some time $t=t_{*}$, the evolution backwards in time from $t_0$ reaches generically a mathematical singularity where $a(t)$ vanishes and the Hubble parameter becomes singular. We determine the general behavior near the singularity. The classical homogeneous inflaton description turns to be valid for $t-t_{*}>10t_{\mathrm{Planck}}$ well before the beginning of inflation, quantum loop effects are negligible there. The singularity is never reached in the validity region of the classical treatment and therefore it is not a real physical phenomenon here. Fast-roll and slow-roll regimes are analyzed in detail including the equation of state evolution, both analytically and numerically. The characteristic time scale of the fast-roll era turns to be $t_1=(1/m)\sqrt{V(0)/[3M^4]}\sim {10}^4{t}_{\mathrm{Planck}}$, where $V$ is the double-well inflaton potential, $m$ is the inflaton mass, and $M$ the energy scale of inflation. The whole evolution of the fluctuations along the decelerated and inflationary fast-roll and slow-roll eras is computed. The Bunch-Davies initial conditions are generalized for the present case in which the potential felt by the fluctuations can never be neglected. The fluctuations feel a singular attractive potential near the $t=t_{*}$ singularity (as in the case of a particle in a central singular potential) with exactly the critical strength ($-1/4$) allowing the fall to the center. Precisely, the fluctuations exhibit logarithmic behavior describing the fall to $t=t_{*}$. The power spectrum gets dynamically modified by the effect of the fast-roll eras and the choice of Bunch-Davies initial conditions at a finite time through the transfer function $D(k)$ of initial conditions. The power spectrum vanishes at $k=0.D(k)$ presents a first peak for $k\sim 2/{\eta }_0$ (${\eta }_0$ being the conformal initial time), then oscillates with decreasing amplitude and vanishes asymptotically for $k\to \infty$. The transfer function $D(k)$ affects the low cosmic microwave background multipoles $C_{\ell }$: the change $\Delta C_{\ell }/C_{\ell }$ for $1\le \ell \le 5$ is computed as a function of the starting instant of the fluctuations $t_0$. Cosmic microwave background quadrupole observations indicate large suppressions, which are well reproduced for the range $t_0-t_{*}\gtrsim 0.05/m\simeq 10100t_{\mathrm{Planck}}$.