In this report we propose the $Z\to \gamma \gamma$ decay as a process strictly forbidden in the standard model, suitable for the search of noncommutativity of coordinates at very short distances. We computed the $Z\to \gamma \gamma$ partial width in the framework of the recently proposed one-loop renormalizable gauge sector of the noncommutative standard model. New experimental possibilities at the Large Hadron Collider are analyzed and a firm bound to the scale of noncommutativity parameter is set around 1 TeV.

We show that the earth matter effects in the ${\nu }_{\mathrm{e}}$ survival probability can be used to cleanly determine the third leptonic mixing angle ${\theta }_{13}$ and the sign of the atmospheric neutrino mass squared difference, $\Delta m_{31}^2$, using a $\beta$-beam as a ${\nu }_e$ source.

Sterile neutrino (${\nu }_s$) conversion in meter scale baselines can be sensitively probed using monoenergetic, sub-MeV, flavor-pure ${\nu }_e$’s from an artificial Megacurie source and the unique technology of the LENS low energy solar ${\nu }_e$ detector. Active-sterile oscillations can be directly observed in the granular LENS detector itself to critically test and extend results of short baseline accelerator and reactor experiments.

We report on a search for the exclusive two-body charmless hadronic $B$ meson decays $B\to {\eta }^{\prime }\rho$, $B\to {\eta }^{\prime }{K}^{*}$, $B^0\to {\eta }^{\prime }\varphi$, $B^0\to {\eta }^{\prime }\omega$, and $B^0\to {\eta }^{\prime }{\eta }^{(\prime )}$. The results are obtained from a data sample containing $535\times {10}^6$ $B\overline{B}$ pairs that were collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We find no significant signals and report upper limits in the range $(0.5–6.5)\times {10}^{-6}$ for all of the above decays.

Little Higgs models with $T$ Parity contain new vectorlike fermions, the $T$-odd quarks or “TOQ’s”, which can be produced at hadron colliders with a QCD-strength cross section. Events with two acoplanar jets and large missing transverse energy provide a simple signature of TOQ production. We show that searches for this signature with the Tevatron Run II data can probe a significant part of the Little Higgs model parameter space not accessible to previous experiments, exploring TOQ masses up to about 400 GeV. This reach covers parts of the parameter space where the lightest $T$-odd particle can account for the observed dark matter relic abundance. We also comment on the prospects for this search at the Large Hadron Collider (LHC).

We show that the spontaneous breakdown of U(1) symmetry in a Higgs model can be described in discretized light cone formulation even by neglecting zero mode. We obtain correctly the energy of a ground state with the symmetry breakdown. We also show explicitly the presence of a Goldstone mode and its absence when the U(1) symmetry is gauged. In spite of obtaining the favorable results, we lose a merit in the formulation without zero modes that a naive Fock vacuum is the true ground state.

We utilize a recent formulation of a spherically symmetric spacetime endowed with a general decomposition of the energy-momentum tensor [Phys. Rev. D 75, 024031 (2007)] to derive equations governing spherically symmetric distributions of electromagnetic matter. We show the system reduces to the Reissner-Nordstrom spacetime in general, spherically symmetric coordinates in the vacuum limit. Furthermore, we show reduction to the charged Vaidya spacetime in non-null coordinates when certain equations of states are chosen. A model of gravitational collapse is discussed whereby a charged fluid resides within a boundary of finite radial extent on the initial hypersurface, and is allowed to radiate charged particles. Our formalism allows for the discussion of all regions in this model without the need for complicated matching schemes at the interfaces between successive regions. As further examples we consider the collapse of a thin shell of charged matter onto a Reissner-Nordstrom black hole. Finally, we reduce the entire system of equations to the static case such that we have the equations for hydrostatic equilibrium of a charged fluid.

We include the effect of neutrino free streaming into the spectrum of relic gravitational waves (RGWs) in the currently accelerating universe. For the realistic case of a varying fractional neutrino energy density and a nonvanishing derivative of the mode function at the neutrino decoupling, the integro-differential equation of RGWs is solved by a perturbation method for the period from the neutrino decoupling to the matter-dominant stage. Incorporating it into the analytic solution of RGWs for the whole history of expansion of the universe, the analytic solution of RGWs is obtained, evolving from inflation up to the current acceleration. The resulting spectrum of RGWs covers the whole range of frequency $({10}^{-19}–{10}^{10})\mathrm{Hz}$ and improves the previous results. It is found that neutrino free streaming causes a reduction of the spectral amplitude by $\sim 20\%$ in the range $({10}^{-16}–{10}^{-10})\mathrm{Hz}$, and leaves the other portion of the spectrum almost unchanged. This agrees with the earlier numerical calculations. Examination is made on the difference between the accelerating and nonaccelerating models, and our analysis shows that the ratio of the spectral amplitude in the accelerating $\Lambda \mathrm{CDM}$ model over that in the CDM model is $\sim 0.7$, and within the various accelerating models of ${\Omega }_{\Lambda }>{\Omega }_m$ the spectral amplitude is proportional to ${\Omega }_m/{\Omega }_{\Lambda }$ for the whole range of frequency. Comparison with LIGO S5 run sensitivity shows that RGWs are not yet detectable by the present LIGO, and in the future LISA may be able to detect RGWs in some inflationary models.

At the largest angular scales the presence of a number of unexpected features has been confirmed by the latest measurements of the cosmic microwave background (CMB). Among them are the anomalous alignment of the quadrupole and octopole with each other as well as the stubborn lack of angular correlation on scales $>60°$. We search for correlations between these two phenomena and demonstrate their absence. A Monte Carlo likelihood analysis confirms previous studies and shows that the joint likelihood of both anomalies is incompatible with the best-fit $\Lambda$ cold dark matter model at $>99.95\%$ C.L. Extending also to higher multipoles, a common special direction (the “Axis of Evil”) has been identified. In the search for an explanation of the anomalies, several studies invoke effects that exhibit an axial symmetry. We find that this interpretation of the “Axis of Evil” is inconsistent with three-year data from the Wilkinson Microwave Anisotropy Probe (WMAP). The data require a preferred plane, whereupon the axis is just the normal direction. Rotational symmetry within that plane is ruled out at high confidence.

We report the results of a five-year survey of the northern sky to search for point sources of high energy neutrinos. The search was performed on the data collected with the AMANDA-II neutrino telescope in the years 2000 to 2004, with a live time of 1001 days. The sample of selected events consists of 4282 upward going muon tracks with high reconstruction quality and an energy larger than about 100 GeV. We found no indication of point sources of neutrinos and set 90% confidence level flux upper limits for an all-sky search and also for a catalog of 32 selected sources. For the all-sky search, our average (over declination and right ascension) experimentally observed upper limit ${\Phi }^0=(\frac{E}{1\mathrm{TeV}}{)}^{\gamma }·\frac{d\Phi }{dE}$ to a point source flux of muon and tau neutrino (detected as muons arising from taus) is ${\Phi }_{{\nu }_{\mu }+{\overline{\nu }}_{\mu }}^0+{\Phi }_{{\nu }_{\tau }+{\overline{\nu }}_{\tau }}^0=11.1\times {10}^{-11}{\mathrm{TeV}}^{-1}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$, in the energy range between 1.6 TeV and 2.5 PeV for a flavor ratio ${\Phi }_{{\nu }_{\mu }+{\overline{\nu }}_{\mu }}^0/{\Phi }_{{\nu }_{\tau }+{\overline{\nu }}_{\tau }}^0=1$ and assuming a spectral index $\gamma =2$. It should be noticed that this is the first time we set upper limits to the flux of muon and tau neutrinos. In previous papers we provided muon neutrino upper limits only neglecting the sensitivity to a signal from tau neutrinos, which improves the limits by 10% to 16%. The value of the average upper limit presented in this work corresponds to twice the limit on the muon neutrino flux ${\Phi }_{{\nu }_{\mu }+{\overline{\nu }}_{\mu }}^0=5.5\times {10}^{-11}{\mathrm{TeV}}^{-1}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$. A stacking analysis for preselected active galactic nuclei and a search based on the angular separation of the events were also performed. We report the most stringent flux upper limits to date, including the results of a detailed assessment of systematic uncertainties.

Recently, a holographic argument was used to relate the saturation exponent, ${\gamma }_{\mathrm{BFKL}}$, of 4-dimensional Yang-Mills theory in the Regge limit to the Choptuik critical scaling exponent, ${\gamma }_{5d}$, in 5-dimensional black hole formation via scalar field collapse [L. Álvarez-Gaumé, C. Gómez, and M. A. Vázquez-Mozo, arXiv:hep-th/0611312.]. Remarkably, the numerical value of the former agreed quite well with previous calculations of the latter. We present new results of an improved calculation of ${\gamma }_{5d}$ with substantially decreased numerical error. Our current result is ${\gamma }_{5d}=0.4131\pm 0.0001$, which is close to, but not in strict agreement with, the value of ${\gamma }_{\mathrm{BFKL}}=0.409552$ quoted in [L. Álvarez-Gaumé, C. Gómez, and M. A. Vázquez-Mozo, arXiv:hep-th/0611312.].

We analyze the effect of a form factor in the magnetic contribution to $K^{+}\to {\pi }^{+}{\pi }^0\gamma$. We emphasize how this can show up experimentally; in particular, we try to explore the difference between a possible interference contribution and a form factor in the magnetic part. The form factor used for $K^{+}\to {\pi }^{+}{\pi }^0\gamma$ is analogous to the one for $K_L\to {\pi }^{+}{\pi }^{-}\gamma$, experimentally well established.

A recent work showing that homogeneous and isotropic cosmologies involving scalar fields are equivalent to the geodesics of certain effective manifolds is generalized to the nonminimally coupled and anisotropic cases. As the Maupertuis-Jacobi principle in classical mechanics, such a result permits us to infer some dynamical properties of cosmological models from the geometry of the associated effective manifolds, allowing us to go a step further in the study of cosmological dynamics. By means of some explicit examples, we show how the geometrical analysis can simplify considerably the dynamical analysis of cosmological models.

We reassess a work done by Migdal on the spectrum of low-energy vector mesons in QCD in the light of the anti-de Sitter (AdS)-QCD correspondence. Recently, a tantalizing parallelism was suggested between Migdal’s work and a family of holographic duals of QCD. Despite the intriguing similarities, both approaches face a major drawback: the spectrum is in conflict with well-tested Regge scaling. However, it has recently been shown that holographic duals can be modified to accommodate Regge behavior. Therefore, it is interesting to understand whether Regge behavior can also be achieved in Migdal’s approach. In this paper we investigate this issue. We find that Migdal’s approach, which is based on a modified Padé approximant, is closely related to the issue of quark-hadron duality breakdown in QCD.

We construct noncommutative $U(1)$ gauge theory on the fuzzy sphere $S_N^2$ as a unitary $2N\times 2N$ matrix model. In the quantum theory the model is equivalent to a non-Abelian $U(N)$ Yang-Mills theory on a two-dimensional lattice with two plaquettes. This equivalence holds in the “fuzzy sphere” phase where we observe a 3rd order phase transition between weak-coupling and strong-coupling phases of the gauge theory. In the matrix phase we have a $U(N)$ gauge theory on a single point.

In the construction of a classical smoothed out brane world model in five dimensions, one uses a dynamically generated domain wall (a kink) to localize an effective four dimensional theory. At the level of the Euler-Lagrange equations the kink sets up a potential well, a mechanism which has been employed extensively to obtain localized, four dimensional, massless chiral fermions. We present the generalization of this kink trapping mechanism for both scalar and fermionic fields, and retain all degrees of freedom that were present in the higher dimensional theory. We show that a kink background induces a symmetric modified Pöschl-Teller potential well, and give explicit analytic forms for all the bound modes and a restricted set of the continuum modes. We demonstrate that it is possible to confine an effective four dimensional scalar field with a quartic potential of arbitrary shape. This can be used to place the standard model electroweak Higgs field on the brane, and also generate nested kink solutions. We also consider the limits of the parameters in the theory which give thin kinks and localized and delocalized scalar and fermionic fields.

We discuss the emission of gravitational radiation produced in encounters of dark matter galactic halos. To this aim we perform a number of numerical simulations of typical galaxy mergers, computing the associated gravitational radiation waveforms as well as the energy released in the processes. Our simulations yield dimensionless gravitational wave amplitudes of the order of ${10}^{-13}$ and gravitational wave frequencies of the order of ${10}^{-16}\mathrm{Hz}$, when the galaxies are located at a distance of 10 Mpc. These values are of the same order as those arising in the gravitational radiation originated by strong variations of the gravitational field in the early Universe, and therefore, such gravitational waves cannot be directly observed by ground-based detectors. We discuss the feasibility of an indirect detection by means of the $B$-mode polarization of the cosmic microwave background (CMB) induced by such waves. Our results show that the gravitational waves from encounters of dark matter galactic halos leave much too small an imprint on the CMB polarization to be actually observed with ongoing and future missions.

Local observation is an important problem both for the foundations of a quantum theory of gravity and for applications to quantum-cosmological problems such as eternal inflation. While gauge-invariant local observables cannot be defined, it has been argued that appropriate relational observables approximately reduce to local observables in certain states. However, quantum mechanics and gravity together imply limitations on the precision of their localization. Such a relational framework is studied in the context of two-dimensional gravity, where there is a high degree of analytic control. This example furnishes a concrete example of some of the essential features of relational observables.

We investigate analytically both the intermediate and late-time behavior of the massive scalar field in the background of the static spherically symmetric black hole solution in dilaton gravity with an arbitrary coupling constant. The intermediate asymptotic behavior of the scalar field depends on the field’s parameter mass as well as the multiple number $l$. On its turn, the late-time behavior has the power-law decay rate independent on the coupling constant in the theory under consideration.

We study the three-body baryonic $B$ decays of $B\to p\overline{p}(K^{*},\rho )$ in the standard model. The baryonic matrix elements are calculated in terms of the $SU(3)$ flavor symmetry and the QCD power counting rules within the perturbative QCD. We find that the decay branching ratios, angular, and direct $CP$ asymmetries of ($B^{-}\to p\overline{p}{K}^{*-}$, ${\overline{B}}^0\to p\overline{p}{K}^{*0}$, $B^{-}\to p\overline{p}{\rho }^{-}$) are around $(6,1,30)\times {10}^{-6}$, $(13,-27,11)\%$, and $(22,1,-3)\%$, which are consistent with the current BABAR and Belle data, respectively. The large values of the branching ratio in $B^{-}\to p\overline{p}{\rho }^{-}$ and the direct $CP$ asymmetry in $B^{\pm }\to p\overline{p}{K}^{*\pm }$ are useful to test the standard model and search for new physics.