The average phase factor $⟨e^{2i\theta }⟩$ of the QCD determinant is evaluated at the finite quark chemical potential (${\mu }_{\mathrm{q}}$) with the two-flavor version of the Polyakov-loop extended Nambu–Jona-Lasinio model with the scalar-type eight-quark interaction. For ${\mu }_{\mathrm{q}}$ larger than half the pion mass $m_{\pi }$ at vacuum, $⟨e^{2i\theta }⟩$ is finite only when the Polyakov loop is larger than $\sim 0.5$, indicating that lattice QCD is feasible only in the deconfinement phase. A critical end point lies in the region of $⟨e^{2i\theta }⟩=0$. The scalar-type eight-quark interaction makes it shorter a relative distance of the critical end point to the boundary of the region. For ${\mu }_{\mathrm{q}}<m_{\pi }/2$, the Polyakov-loop extended Nambu–Jona-Lasinio model with dynamical mesonic fluctuations can reproduce lattice QCD data below the critical temperature.

We provide a comprehensive study of strong coupling constants of decuplet baryons with light nonet vector mesons in the framework of light cone QCD sum rules. Using the symmetry arguments, we argue that all coupling constants entering the calculations can be expressed in terms of only one invariant function even if the $SU(3{)}_f$ symmetry breaking effects are taken into account. We estimate the order of $SU(3{)}_f$ symmetry violations, which are automatically considered by the employed approach.

We investigate the experimentally allowed parameter space of an extension of the standard model (SM3) by one additional family of fermions. Therefore we extend our previous study of the Cabibbo-Kobayashi-Maskawa (CKM)–like mixing constraints of a fourth generation of quarks. In addition to the bounds from tree-level determinations of the $3\times 3$ CKM elements and flavor-changing neutral currents processes ($K$, $D$, $B_d$, $B_s$ mixing and the decay $b\to s\gamma$) we also investigate the electroweak $S$, $T$, $U$ parameters, the angle $\gamma$ of the unitarity triangle, and the rare decay $B_s\to {\mu }^{+}{\mu }^{-}$. Moreover we improve our treatment of the QCD corrections compared to our previous analysis. We also take leptonic contributions into account, but we neglect the mixing among leptons. As a result we find that typically small mixing with the fourth family is favored, but still some sizeable deviations from the SM3 results are not yet excluded. The minimal possible value of $V_{tb}$ is 0.93. Also very large $CP$-violating effects in $B_s$ mixing seem to be impossible within an extension of the SM3 that consists of an additional fermion family alone. We find a delicate interplay of electroweak and flavor observables, which strongly suggests that a separate treatment of the two sectors is not feasible. In particular we show that the inclusion of the full CKM dependence of the $S$ and $T$ parameters in principle allows the existence of a degenerate fourth generation of quarks.

We investigate the detectability of neutralino dark matter via direct and indirect searches as well as collider signatures of an $SO(10)$ model with two intermediate scales. We compare the direct dark matter detection cross section and the muon flux due to neutralino annihilation in the Sun that we obtain in this model with minimal supergravity predictions and with the sensitivity of current and future experiments. In both cases, we find that the detectability improves as the model deviates more from minimal supergravity. In order to study collider signatures, we choose two benchmark points that represent the main phenomenological features of the model: a lower value of $|\mu |$ and reduced third-generation sfermion masses due to extra Yukawa coupling contributions in the renormalization group equations and increased first- and second-generation slepton masses due to new gaugino loop contributions. We show that measurements at the LHC can distinguish this model from minimal supergravity in both cases, by counting events containing leptonically decaying $Z^0$ bosons, heavy neutral Higgs bosons, or like-sign lepton pairs. The methods we develop can be used more generally to characterize models of weak-scale supersymmetry.

The pion masses and the pion decay constant are calculated to 1-loop order in SU(2) twisted mass Wilson chiral perturbation theory, assuming a large pion mass splitting and tuning to maximal twist. Taking the large mass splitting at leading order in the chiral expansion leads to significant modifications in the chiral logarithms. For example, the result for the charged pion mass contains a chiral logarithm that involves the neutral pion mass instead of the charged one. Similar modifications appear in the results for the neutral pion mass and the decay constant. These new results are used in fits to lattice data obtained recently by the European twisted mass collaboration. The data can be fitted well, in general better than with the standard chiral perturbation theory expressions that ignore the mass splitting. The impact on the extraction of low-energy couplings is briefly discussed.

We calculate the fermionic corrections to the photon-energy spectrum of $\overline{B}\to X_s\gamma$ which arise from the self-interference of the chromomagnetic dipole operator $Q_8$ at next-to-next-to-leading order by applying naive non-Abelianization. The resulting $\mathcal{O}({\beta }_0{\alpha }_s^2)$ correction to the $\overline{B}\to X_s\gamma$ branching ratio amounts to a relative shift of $+0.12\%$ ($+0.27\%$) for a photon-energy cut of 1.6 GeV (1.0 GeV). We also comment on the potential size of resummation and nonperturbative effects related to $Q_8$.

Both D0 and CDF at Tevatron reported the measurements of forward-backward asymmetry in top pair production, which showed possible deviation from the standard model QCD prediction. In this paper, we explore how to examine the same higher-order QCD effects at the more powerful Large Hadron Collider.

The Belle Collaboration observed an enhancement called $X(4630)$ in the ${\Lambda }_c^{+}{\Lambda }_c^{-}$ mass distribution using initial state radiation. We demonstrate that the enhancement could be consistent with the ${\psi }^{\prime }{f}_0(980)$ molecular picture of the $Y(4660)$ taking into account the ${\Lambda }_c^{+}{\Lambda }_c^{-}$ final state interaction. To test the hypothesis that the $X(4630)$ and $Y(4660)$ are the same molecular state, we give predictions for its spin partner, the ${\eta }_c^{\prime }{f}_0(980)$ molecule. High statistic measurements of the $B$ decays into the $K{\Lambda }_c^{+}{\Lambda }_c^{-}$ and $K{\eta }_c^{\prime }{\pi }^{+}{\pi }^{-}$ are strongly recommended.

Static quark-antiquark potential encodes important information on the chromodynamical interaction between color charges, and recent lattice results show its very nontrivial behavior near the deconfinement temperature $T_c$. In this paper we study such potential in the framework of the “magnetic scenario” for the near $T_c$ QCD plasma, and particularly focus on the linear part (as quantified by its slope, the tension) in the potential as well as the strong splitting between the free energy and internal energy. By using an analytic “ellipsoidal bag” model, we will quantitatively relate the free energy tension to the magnetic condensate density and relate the internal energy tension to the thermal monopole density. By converting the lattice results for static potential into density for thermal monopoles we find the density to be very large around $T_c$ and indicate at quantum coherence, in good agreement with direct lattice calculation of such density. A few important consequences for heavy ion collisions phenomenology will also be discussed.

The decays $D^0\to \gamma \gamma$, ${\mu }^{+}{\mu }^{-}$ are highly suppressed in the standard model (SM) with the lion’s share of the rate coming from long distance dynamics; $D^0\to {\mu }^{+}{\mu }^{-}$ is driven predominantly by $D^0\to \gamma \gamma \to {\mu }^{+}{\mu }^{-}$. Their present experimental bounds are small, yet much larger than SM predictions. New physics models like the littlest Higgs models with $T$ parity (LHT) can induce even large indirect $CP$ violation in $D^0$ transitions. One would guess that LHT has a “fighting chance” to affect these $D^0\to \gamma \gamma$, ${\mu }^{+}{\mu }^{-}$ rates in an observable way. We have found LHT contributions can be much larger than short distance SM amplitude by orders of magnitude. Yet those can barely compete with the long distance SM effects. If $D^0\to \gamma \gamma$, ${\mu }^{+}{\mu }^{-}$ modes are observed at greatly enhanced rates, LHT scenarios will not be candidates for generating such signals. LHT-like frameworks will not yield larger $D^0\to \gamma \gamma /{\mu }^{+}{\mu }^{-}$ rates as they are constrained by $B$ and $K$ rare decays.

We study the orbital angular momentum structure of the quarks inside the proton. By employing the light-cone diquark model and the overlap representation formalism, we calculate the chiral-even generalized parton distribution functions $H_q(x,\xi ,{\Delta }^2)$, ${\tilde{H}}_q(x,\xi ,{\Delta }^2)$, and $E_q(x,\xi ,{\Delta }^2)$ at zero skewedness for $q=u$ and $d$ quarks. In our model, $E_u$ and $E_d$ have opposite sign with similar size. Those generalized parton distribution functions are applied to calculate the orbital angular momentum distributions, showing that $L_u(x)$ is positive, while $L_d(x)$ is consistent with zero compared with $L_u(x)$. We introduce the impact parameter dependence of the quark orbital angular momentum distribution. It describes the position space distribution of the quark orbital angular momentum at given $x$. We found that the impact parameter dependence of the quark orbital angular momentum distribution is axially symmetric in the light-cone diquark model.

The phase diagram of strongly interacting matter is studied within a three-flavor Nambu–Jona-Lasinio model, which contains the coupling between chiral and diquark condensates through the axial anomaly. Our results show that it is essential to include the two-flavor color superconducting (2SC) phase in the analysis. While this is expected for realistic strange-quark masses, we find that even for equal up, down, and strange bare quark masses 2SC pairing can be favored due to spontaneous flavor symmetry breaking by the axial anomaly. This can lead to a rich phase structure, including BCS- and Bose-Einstein condensate-like 2SC and color-flavor locked phases and new endpoints. On the other hand, the low-temperature critical endpoint, which was found earlier in the same model without 2SC pairing, is almost removed from the phase diagram and cannot be reached from the low-density chirally broken phase without crossing a preceding first-order phase boundary. For physical quark masses no additional critical endpoint is found.

We report on a search for the flavor-changing neutral-current decay $D^0\to {\mu }^{+}{\mu }^{-}$ in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ using $360{\mathrm{pb}}^{-1}$ of integrated luminosity collected by the CDF II detector at the Fermilab Tevatron collider. A displaced vertex trigger selects long-lived $D^0$ candidates in the ${\mu }^{+}{\mu }^{-}$, ${\pi }^{+}{\pi }^{-}$, and $K^{-}{\pi }^{+}$ decay modes. We use the Cabibbo-favored $D^0\to K^{-}{\pi }^{+}$ channel to optimize the selection criteria in an unbiased manner, and the kinematically similar $D^0\to {\pi }^{+}{\pi }^{-}$ channel for normalization. We set an upper limit on the branching fraction $\mathcal{B}(D^0\to {\mu }^{+}{\mu }^{-})<2.1\times {10}^{-7}(3.0\times {10}^{-7})$ at the 90% (95%) confidence level.

We present the result of a search for charge asymmetry in $B^{\pm }\to J/\psi K^{\pm }$ decays using $772\times {10}^6$ $B\overline{B}$ pairs collected at the ${\rm Y}(4S)$ resonance by the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. The $CP$-violating charge asymmetry is measured to be $A_{CP}(B^{+}\to J/\psi K^{+})=[-0.76\pm 0.50(\mathrm{stat})\pm 0.22(\mathrm{syst})]\%$.

The absolute branching fractions for the decays $D_s^{-}\to {\ell }^{-}{\overline{\nu }}_{\ell }$ ($\ell =e$, $\mu$, or $\tau$) are measured using a data sample corresponding to an integrated luminosity of $521{\mathrm{fb}}^{-1}$ collected at center-of-mass energies near 10.58 GeV with the BABAR detector at the PEP-II $e^{+}{e}^{-}$ collider at SLAC. The number of $D_s^{-}$ mesons is determined by reconstructing the recoiling system $DKX\gamma$ in events of the type $e^{+}{e}^{-}\to DKX{D}_s^{*-}$, where $D_s^{*-}\to D_s^{-}\gamma$ and $X$ represents additional pions from fragmentation. The $D_s^{-}\to {\ell }^{-}{\nu }_{\ell }$ events are detected by full or partial reconstruction of the recoiling system $DKX\gamma \ell$. The branching fraction measurements are combined to determine the $D_s^{-}$ decay constant $f_{D_s}=(258.6\pm 6.4\pm 7.5)\mathrm{MeV}$, where the first uncertainty is statistical and the second is systematic.

We study $k$-defects—topological defects in theories with more than two derivatives and second-order equations of motion—and describe some striking ways in which these defects both resemble and differ from their analogues in canonical scalar field theories. We show that, for some models, the homotopy structure of the vacuum manifold is insufficient to establish the existence of $k$-defects, in contrast to the canonical case. These results also constrain certain families of Dirac-Born-Infeld instanton solutions in the 4-dimensional effective theory. We then describe a class of $k$-defect solutions, which we dub “doppelgängers,” that precisely match the field profile and energy density of their canonical scalar field theory counterparts. We give a complete characterization of Lagrangians which admit doppelgänger domain walls. By numerically computing the fluctuation eigenmodes about domain wall solutions, we find different spectra for doppelgängers and canonical walls, allowing us to distinguish between $k$-defects and the canonical walls they mimic. We search for doppelgängers for cosmic strings by numerically constructing solutions of Dirac-Born-Infeld and canonical scalar field theories. Despite investigating several examples, we are unable to find doppelgänger cosmic strings, hence the existence of doppelgängers for defects with codimension $>1$ remains an open question.

In this paper we present a new numerical code based on the Galerkin method to integrate the field equations for the spherical collapse of massive and massless scalar fields. By using a spectral decomposition in terms of the radial coordinate, the field equations were reduced to a finite set of ordinary differential equations in the space of modes associated with the Galerkin expansion of the scalar field, together with algebraic sets of equations connecting modes associated with the metric functions. The set of ordinary differential equations with respect to the null coordinate is then integrated using an eighth-order Runge-Kutta method. The numerical tests have confirmed the high accuracy and fast convergence of the code. As an application we have evaluated the whole spectrum of black hole masses which ranges from infinitesimal to large values obtained after varying the amplitude of the initial scalar field distribution. We have found strong numerical evidence that this spectrum is described by a nonextensive distribution law.

We investigate features of perturbative gravity and supergravity by studying scattering in the ultra-Planckian limit, and sharpen arguments that the dynamics is governed by long-distance physics. A simple example capturing aspects of the eikonal resummation suggests why short-distance phenomena and, in particular, divergences or nonrenormalizability do not necessarily play a central role in this regime. A more profound problem is apparently unitarity. These considerations can be illustrated by showing that known gravity and supergravity amplitudes have the same long-distance behavior, despite the extra light states of supergravity, and this serves as an important check on long-range dynamics in a context where perturbative amplitudes are finite. We also argue that these considerations have other important implications: they obstruct both probing the conjectured phenomenon of asymptotic safety through a physical scattering process, and ultra-Planckian scattering exhibiting Regge behavior. These arguments sharpen the need to find a nonperturbative completion of gravity with mechanisms which restore unitarity in the strong gravity regime.

We examine bound orbits of particles around singly rotating black rings. We show that there exist stable bound orbits in toroidal spiral shape near the “axis” of the ring, and also stable circular orbits on the axis as special cases. The stable bound orbits can have arbitrary large size if the thickness of the ring is less than a critical value.

We analyze the Drell-Yan lepton pair production at forward rapidity at the Large Hadron Collider. Using the dipole framework for the computation of the cross section we find a significant suppression in comparison to the collinear factorization formula due to saturation effects in the dipole cross section. We develop a twist expansion in powers of $Q_s^2/M^2$ where $Q_s$ is the saturation scale and $M$ the invariant mass of the produced lepton pair. For the nominal LHC energy the leading twist description is sufficient down to masses of 6 GeV. Below that value the higher twist terms give a significant contribution.