We consider the sensitivity of fixed-target neutrino experiments at the luminosity frontier to light stable states, such as those present in models of MeV-scale dark matter. To ensure the correct thermal relic abundance, such states must annihilate via light mediators, which in turn provide an access portal for direct production in colliders or fixed targets. Indeed, this framework endows the neutrino beams produced at fixed-target facilities with a companion “dark matter beam,” which may be detected via an excess of elastic scattering events off electrons or nuclei in the (near-)detector. We study the high-luminosity proton fixed-target experiments at LSND and MiniBooNE, and determine that the ensuing sensitivity to light dark matter generally surpasses that of other direct probes. For scenarios with a kinetically-mixed $\mathrm{U}(1{)}^{\prime }$ vector mediator of mass $m_V$, we find that a large volume of parameter space is excluded for $m_{\mathrm{DM}}\sim 1–5\mathrm{MeV}$, covering vector masses $2m_{\mathrm{DM}}\lesssim m_V\lesssim m_{\eta }$ and a range of kinetic mixing parameters reaching as low as $\kappa \sim {10}^{-5}$. The corresponding MeV-scale dark matter scenarios motivated by an explanation of the galactic 511 keV line are thus strongly constrained.

We present a comprehensive analysis of the electromagnetic form factors of the nucleon from a lattice simulation with two flavors of dynamical $\mathcal{O}(a)$-improved Wilson fermions. A key feature of our calculation is that we make use of an extensive ensemble of lattice gauge field configurations with four different lattice spacings, multiple volumes, and pion masses down to $m_{\pi }\sim 180\mathrm{MeV}$. We find that by employing Kelly-inspired parametrizations for the $Q^2$ dependence of the form factors, we are able to obtain stable fits over our complete ensemble. Dirac and Pauli radii and the anomalous magnetic moments of the nucleon are extracted and results at light quark masses provide evidence for chiral nonanalytic behavior in these fundamental observables.

Photon structure functions in supersymmetric QCD are investigated in terms of the parton model where squark contributions are evaluated. We calculate the eight virtual photon structure functions by taking the discontinuity of the squark massive one-loop diagrams of the photon-photon forward amplitude. The model-independent positivity constraints derived from the Cauchy-Schwarz inequalities are satisfied by the squark parton model calculation and actually the two equality relations hold for the squark contribution. We also show that our polarized photon structure function $g_1^{\gamma }$ for the real photon leads to the vanishing first moment sum rule, and the constraint $|g_1^{\gamma }|\le F_1^{\gamma }$ is satisfied by the real photon. We also discuss a squark signature in the structure function $W_{TT}^{\tau }$.

Advantages of the original symmetrical form of the parametrization of the lepton mixing matrix are discussed. It provides a conceptually more transparent description of neutrino oscillations and lepton number violating processes like neutrinoless double beta decay, clarifying the significance of Dirac and Majorana phases. It is also ideal for parametrizing scenarios with light sterile neutrinos.

The magnetic dipole moment and the electric dipole moment of leptons are calculated under the assumption of lepton flavor violation (LFV) induced by spin-1 unparticles with both vector and axial-vector couplings to leptons, including a $CP$-violating phase. The experimental limits on the muon magnetic dipole moment and LFV process, such as the decay ${\ell }_i^{-}\to {\ell }_j^{-}{\ell }_k^{-}{\ell }_k^{+}$, are then used to constrain the LFV couplings for particular values of the unparticle operator dimension $d_{\mathcal{U}}$ and the unparticle scale ${\Lambda }_{\mathcal{U}}$, assuming that LFV transitions between the tau and muon leptons are dominant. It is found that the current experimental constraints favor a scenario with dominance of the vector couplings over the axial-vector couplings. We also obtain estimates for the electric dipole moments of the electron and the muon, which are well below the experimental values.

A canonical ensemble algorithm is employed to study the phase diagram of $N_f=3$ QCD using lattice simulations. We lock in the desired quark number sector using an exact Fourier transform of the fermion determinant. We scan the phase space below $T_c$ and look for an $S$-shape structure in the chemical potential, which signals the coexistence phase of a first order phase transition in finite volume. Applying Maxwell construction, we determine the boundaries of the coexistence phase at three temperatures and extrapolate them to locate the critical point. Using an improved gauge action and improved Wilson fermions on lattices with a spatial extent of 1.8 fm and quark masses close to that of the strange, we find the critical point at $T_E=0.925(5)T_c$ and baryon chemical potential ${\mu }_B^E=2.60(8)T_c$.

We calculate the finite size correction on the three-point correlation function between two giant magnons and one marginal operator, which is dual to a dilaton field of the bulk gravity theory. We also check that the structure constant in the string setup is exactly the same as one of the renormalization group analyses in the gauge theory.

We discuss the prospects of detecting the sources of ultrahigh energy (UHE) cosmic ray (CR) nuclei via their emission of cosmogenic $\gamma$ rays in the GeV to TeV energy range. These $\gamma$ rays result from electromagnetic cascades initiated by high energy photons, electrons, and positrons that are emitted by CRs during their propagation in the cosmic radiation background and are independent of the simultaneous emission of $\gamma$ rays in the vicinity of the source. The corresponding production power by UHE CR nuclei (with mass number $A$ and charge $Z$) is dominated by pion photo production ($\propto A$) and Bethe-Heitler pair production ($\propto Z^2$). We show that the cosmogenic $\gamma$-ray signal from a single steady UHE CR source is typically more robust with respect to variations of the source composition and injection spectrum than the accompanying signal of cosmogenic neutrinos. We study the diffuse emission from the sum of extragalactic CR sources as well as the point-source emission of the closest sources.

Dark Matter direct detection experiments are able to exclude interesting parameter space regions of particle models which predict an important amount of thermal relics. We use recent data to constrain the branon model and to compute the region that is favored by CDMS measurements. Within this work, we also update present colliders constraints with new studies coming from the LHC. Despite the present low luminosity, it is remarkable that for heavy branons, CMS and ATLAS measurements are already more constraining than previous analyses performed with TEVATRON and LEP data.

In this paper we compare the performances of the ${\chi }^2$ and median likelihood analysis in the determination of cosmological constraints using type Ia supernovae data. We perform a statistical analysis using the 307 supernovae of the Union 2 compilation of the Supernova Cosmology Project and find that the ${\chi }^2$ statistical analysis yields tighter cosmological constraints than the median statistic if only supernovae data is taken into account. We also show that when additional measurements from the cosmic microwave background and baryonic acoustic oscillations are considered, the combined cosmological constraints are not strongly dependent on whether one applies the ${\chi }^2$ statistic or the median statistic to the supernovae data. This indicates that, when complementary information from other cosmological probes is taken into account, the performances of the ${\chi }^2$ and median statistics are very similar, demonstrating the robustness of the statistical analysis.

The generalization of the minimal supersymmetric standard model (MSSM) to the case of four chiral fermion generations (4GMSSM) can lead to significant changes in the phenomenology of the otherwise familiar Higgs sector. In most of the 3GMSSM parameter space, the lighter $CP$-even $h$ is $\sim 115–125\mathrm{GeV}$ and mostly standard model–like while $H$, $A$, $H^{\pm }$ are all relatively heavy. Furthermore, the ratio of Higgs vacuum expectation values, $\tan \beta$, is relatively unconstrained. In contrast to this, in the 4GMSSM, heavy fourth-generation fermion loops drive the masses of $h$, $H$, $H^{\pm }$ to large values while the $CP$-odd boson, $A$, can remain relatively light and $\tan \beta$ is restricted to the range $1/2\lesssim \tan \beta \lesssim 2$ due to perturbativity requirements on Yukawa couplings. We explore this scenario in some detail, concentrating on the collider signatures of the light $CP$-odd Higgs at both the Tevatron and LHC. We find that while $gg\to A$ may lead to a potential signal in the ${\tau }^{+}{\tau }^{-}$ channel at the LHC, $A$ might first be observed in the $\gamma \gamma$ channel due to a highly loop-enhanced cross section that can be more than an order of magnitude greater than that of a SM Higgs for $A$ masses of $\sim 100–150\mathrm{GeV}$ and $\tan \beta <1$. We find that the $CP$-even states $h$, $H$ are highly mixed and can have atypical branching fractions. Precision electroweak constraints, particularly for the light $A$ parameter space region, are examined in detail.

Recent LHC searches have not found a clear signal of the Higgs boson $h$ of the standard model (SM) with three or four families in the mass range $m_h=120–600\mathrm{GeV}$. If the Higgs had an unexpectedly large invisible branching ratio, the excluded $m_h$ regions would shrink. This can be realized in the simplest weakly interacting massive particle dark matter (DM) model, which is the SM plus a real gauge-singlet scalar field $D$ as the DM, via the invisible mode $h\to DD$. Current data allow this decay to occur for $D$-mass values near, but below, $m_h/2$ and those compatible with the light DM hypothesis. For such $D$ masses, $h\to DD$ can dominate the Higgs width depending on $m_h$, and thus sizable portions of the $m_h$ exclusion zones in the SM with three or four families may be recovered. Increased luminosity at the LHC may even reveal a Higgs having SM-like visible decays still hiding in the presently disallowed regions. The model also accommodates well the new possible DM hints from CRESST-II and will be further tested by improved data from future DM direct searches.

Using hydrogenic and Gaussian wave functions, mass spectra and decay properties of the $D_s(c\overline{s})$ meson are investigated in the framework of phenomenological quark-antiquark potential (Coulomb plus power) model consisting of a relativistic kinetic energy term. The spin-hyperfine, spin-orbit, and tensor interactions are employed to obtain the pseudoscalar and vector meson masses incorporating the effect of mixing. The decay constants $(f_{P/V})$ are computed with QCD correction using the wave function at the origin. The leptonic branching fractions and electromagnetic transition rates are also calculated in this scheme. Our predictions at potential index $\nu =1$ are in good agreement with experimental results as well as other theoretical models.

We investigate the role played by the three-body $D\overline{D}\pi$ dynamics on the near-threshold resonance $X(3872)$ charmonium state, which is assumed to be formed by nonperturbative $D{\overline{D}}^{*}$ dynamics. It is demonstrated that, as compared to the naive static-pions approximation, the imaginary parts that originate from the inclusion of dynamical pions reduce substantially the width from the $D\overline{D}\pi$ intermediate state. In particular, for a resonance peaked at 0.5 MeV below the $D^0{\overline{D}}^{*0}$ threshold, this contribution to the width is reduced by about a factor of 2, and the effect of the pion dynamics on the width grows as long as the resonance is shifted towards the $D^0{\overline{D}}^0{\pi }^0$ threshold. Although the physical width of the $X$ is dominated by inelastic channels, our finding should still be of importance for the $X$ line shapes in the $D\overline{D}\pi$ channel below $D{\overline{D}}^{*}$ threshold. For example, in the scattering length approximation, the imaginary part of the scattering length includes effects of all the pion dynamics and does not only stem from the $D^{*}$ width. Meanwhile, we find that another important quantity for the $X$ phenomenology, the residue at the $X$ pole, is weakly sensitive to dynamical pions. In particular, we find that the binding energy dependence of this quantity from the full calculation is close to that found from a model with pointlike $D{\overline{D}}^{*}$ interactions only, consistent with earlier claims. Coupled-channel effects (inclusion of the charged $D{\overline{D}}^{*}$ channel) turn out to have a moderate impact on the results.

We present a calculation of the $\mathcal{O}({\alpha }_s)$ QCD corrections to the production of a $Z$ boson in association with two photons and to triple-photon production at hadron colliders. All final-state photons are taken as real. For the $Z$ boson, we consider the decays both into charged leptons and into neutrinos including all off-shell effects. Numerical results are obtained via a Monte Carlo program based on the structure of the VBFNLO program package. This allows us to implement general cuts and distributions of the final-state particles. We find that the next-to-leading order QCD corrections are sizable and significantly exceed the expectations from a scale variation of the leading-order result. In addition, differential distributions of important observables change considerably. The prediction of two-photon-associated $Z$ production with $Z$ decays into neutrinos from the charged-lepton rate works well, once we use an additional cut on the invariant mass of the charged-lepton pair.

We design a supersymmetric $SU(5)$ grand unified theory model using $\Delta (54)$, a finite non-Abelian subgroup of $SU(3{)}_f$. Heavy right-handed neutrinos are introduced which transform as a three-dimensional representation of our chosen family group. The model successfully reproduces the hierarchical structures of the standard model and the Cabibbo-Kobayashi-Maskawa mixing matrix. It then provides predictions for the light neutrinos with a normal hierarchy and masses such that $m_{\nu ,1}\approx 5\times {10}^{-3}\mathrm{eV}$, $m_{\nu ,2}\approx 1\times {10}^{-2}\mathrm{eV}$, and $m_{\nu ,3}\approx 5\times {10}^{-2}\mathrm{eV}$. We also provide predictions for masses of the heavy neutrinos, and corrections to the tribimaximal matrix that fit within experimental limits, e.g., a reactor angle of $-7.31°$. A simple modification to our model is introduced at the end and is shown to also produce predictions that fall well within those limits.

The magnetic moment—a function of the electric charge form factor $F_1(q^2)$ and the magnetic dipole form factor $F_2(q^2)$ at zero four-momentum transfer $q^2$—of the ground-state $J^P={\frac{3}{2}}^{+}$ baryon decuplet magnetic moments have been studied for many years with limited success. At present, only the magnetic moment of the ${\Omega }^{-}$ has been accurately determined. We calculate nonperturbatively the magnetic moments of the physical baryon decuplet $J^P={\frac{3}{2}}^{+}$ members and, in particular, we obtain ${\mu }_{{\Delta }^{++}}=(+3.67\pm 0.07){\mu }_N$, ${\mu }_{{\Delta }^{+}}=(+1.83\pm 0.04){\mu }_N$, ${\mu }_{{\Delta }^0}=(0){\mu }_N$, and the magnetic moments of their $U$-Spin partners in terms of ${\Omega }^{-}$ magnetic moment data.

We discuss how: (i) a dilaton/axion superfield can play the role of a Barbero-Immirzi field in four-dimensional conformal quantum supergravity theories, (ii) a fermionic component of such a dilaton/axion superfield may play the role of a Goldstino in the low-energy effective action obtained from a superstring theory with $F$-type global supersymmetry breaking, (iii) this global supersymmetry breaking is communicated to the gravitational sector via the supergravity coupling of the Goldstino, and (iv) such a scenario may be realized explicitly in a D-foam model with D-particle defects fluctuating stochastically.

We investigate string or branelike solutions for four-dimensional vacuum Einstein equations in the presence of a cosmological constant. For the case of negative cosmological constant, the Bañados-Teitelboim-Zanelli black string is the only warped stringlike solution. The general solutions for nonwarped branelike configurations are found and they are characterized by the Arnowitt-Deser-Misner mass density and two tensions. Interestingly, the sum of these tensions is equal to the minus of the mass density. Other than the well-known black string and soliton spacetimes, all the static solutions possess naked singularities. The time-dependent solutions can be regarded as the anti-de Sitter extension of the well-known Kasner solutions. The speciality of those static regular solutions and the implication of singular solutions are also discussed in the context of cylindrical matter collapse. For the case of positive cosmological constant, the Kasner-de Sitter spacetime appears as time-dependent solutions and all static solutions are found to be naked singular.

We study linear perturbations around static, spherically symmetric spacetimes in $f(R,C)$ gravitational theories whose Lagrangians depend on the Ricci scalar $R$ and the parity violating Chern-Simons term $C$. By an explicit construction, we show that the Hamiltonian for the perturbation variables is not bounded from below, suggesting that such a background spacetime is unstable against perturbations. This gives a strong limit on a phenomenological gravitational model which violates parity. We also show that either $R=\mathrm{const}$ or $\frac{{\partial }^{2}f}{\partial R\partial C}=0$ is a necessary and sufficient condition for the stability. We then implement in detail the perturbation analysis for such theories which satisfy the stability conditions. For $\ell \ge 2$, where $\ell$ is the usual integer for the multipole expansion, the number of propagating modes is three, one from the odd and the other two from the even, all of which propagate at the speed of light. Unlike in the case of $f(R)$ theories, these modes are coupled to each other, which can be used as a distinctive feature to test the parity violating theories from observations. The no-ghost conditions and no-tachyon conditions are the same as those in $f(R)$ theories. For the dipole perturbations, the odd and the even modes completely decouple. The odd mode gives a slowly rotating black hole solution whose metric is linearized in its angular momentum. We provide an integral expression of this solution. On the other hand, the even mode propagates at the speed of light. For the monopole perturbation, in addition to a mode which simply shifts the mass of the background black hole, there also exists one even mode that propagates at the speed of light.