We discuss the structure of topological defects in the context of extra dimensions where the symmetry breaking terms are localized. These defects develop structure in the extra dimension which differs from the case where symmetry breaking is not localized. This new structure can lead to corrections to the mass scale of the defects which is not captured by a simple effective theory obtained by integrating out the extra dimension. We also consider the Higgsless model of symmetry breaking and show that no finite energy defects appear in some situations where they might have been expected.

An $\mathrm{SU}(N_f)\times \mathrm{SU}(N_f)$ Yang-Mills theory on an extra-dimensional interval is considered, with appropriate symmetry-breaking boundary conditions on the IR brane. UV-brane to UV-brane correlators at high energies are compared with the OPE of two-point functions of QCD quark currents. Condensates correspond to departure from the AdS metric of the (different) metrics felt by vector and axial combinations, away from the UV brane. Their effect on hadronic observables is studied: the extracted condensates agree with the signs and orders of magnitude expected from QCD.

The local Casimir energy density for a massless scalar field associated with step-function potentials in a $3+1$ dimensional spherical geometry is considered. The potential is chosen to be zero except in a shell of thickness $\delta$, where it has height $h$, with the constraint $h\delta =1$. In the limit of zero thickness, an ideal $\delta$-function shell is recovered. In this limit, the behavior of the energy density as the surface of the shell is approached is studied in both the strong and weak coupling regimes. The former case corresponds to the well-known Dirichlet shell limit. New results, which shed light on the nature of surface divergences and on the energy contained within the shell, are obtained in the weak coupling limit, and for a shell of finite thickness. In the case of zero thickness, the energy has a contribution not only from the local energy density, but from an energy term residing entirely on the surface. It is shown that the latter coincides with the integrated local energy density within the shell. We also study the dependence of local and global quantities on the conformal parameter. In particular new insight is provided on the reason for the divergence in the global Casimir energy in third order in the coupling.

The Ashtekar-Barbero-Immirzi formulation of general relativity is extended to include spinor matter fields. Our formulation applies to generic values of the Immirzi parameter and reduces to the Ashtekar-Romano-Tate approach when the Immirzi parameter is taken equal to the imaginary unit. The dynamics of the gravity-fermions coupled system is described by the Holst plus Dirac action with a nonminimal coupling term. The nonminimal interaction together with the Holst modification to the Hilbert-Palatini action reconstruct the Nieh-Yan invariant, so that the effective action coming out is the one of Einstein-Cartan theory with a typical Fermi-like interaction term: in spite of the presence of spinor matter fields, the Immirzi parameter plays no role in the classical effective dynamics and results to be only a multiplicative factor in front of a total divergence. We reduce the total action of the theory to the sum of dynamically independent Ashtekar-Romano-Tate actions for self and anti-self-dual connections, with different weights depending on the Immirzi parameter. This allows to calculate the constraints of the complete theory in a simple way, it is only necessary to realize that the Barbero-Immirzi connection is a weighted sum of the self and anti-self-dual Ashtekar connections. Finally the obtained constraints for the separated action result to be polynomial in terms of the self and anti-self-dual connections, this could have implications in the inclusion of spinor matter in the framework of nonperturbative quantum gravity.

Higher-dimensional, direct analogues of the usual $d=4$ Einstein–Yang-Mills (EYM) systems are studied. They feature single members of both the gravitational and the Yang-Mills hierarchies in $d=4p$-dimensional spacetimes, both consisting of $2p$-form curvature terms only. This enables us to probe the effects of higher order gravitational terms, which in the presence of the usual Einstein term would be masked. Regular and black hole solutions are constructed in $2p+2\le d\le 4p$, in which dimensions the total mass-energy is finite, generalizing the familiar Bartnik-McKinnon solutions in EYM theory for $p=1$. In $d=4p$, this similarity is complete. In the special case of $d=2p+1$, just beyond the finite energy range of $d$, exact solutions in closed form are found. Finally, $d=2p+1$ purely gravitational systems, whose solutions generalize the static $d=3$ BTZ solutions, are discussed.

Recent papers by Fewster and Roman have emphasized that wormholes supported by arbitrarily small amounts of exotic matter will have to be incredibly fine-tuned if they are to be traversable. This paper discusses a wormhole model that strikes a balance between two conflicting requirements, reducing the amount of exotic matter and fine-tuning the metric coefficients, ultimately resulting in an engineering challenge: one requirement can only be met at the expense of the other. The wormhole model is macroscopic and satisfies various traversability criteria.

We investigate the Gregory-Laflamme instability for black strings carrying KK momentum along the internal direction. We demonstrate a simple kinematical relation between the thresholds of the classical instability for the boosted and static black strings. We also find that Sorkin’s critical dimension depends on the internal velocity and in fact disappears for sufficiently large boosts. Our analysis implies the existence of an analogous instability for the five-dimensional black ring of Emparan and Reall. We also use our results for boosted black strings to construct a simple model of the black ring and argue that such rings exist in any number of space-time dimensions.

We study the effect of a phenomenological parameterized quintessence model on low, intermediate and high redshift observations. At low and intermediate redshifts, we use the Gold sample of supernova Type Ia (SNIa) data and recently observed size of baryonic acoustic peak from Sloan Digital Sky Survey (SDSS), to put constraint on the parameters of the quintessence model. At the high redshift, the same fitting procedure is done using WAMP data, comparing the location of acoustic peak with that obtain from the dark energy model. As a complementary analysis in a flat universe, we combine the results from the SNIa, CMB and SDSS. The best fit values for the model parameters are ${\Omega }_m={0.27}_{-0.02}^{+0.02}$ (the present matter content) and $w_0=-{1.45}_{-0.60}^{+0.35}$ (dark energy equation of state). Finally we calculate the age of universe in this model and compare it with the age of old stars and high redshift objects.

Detection of ultrahigh energy neutrinos will be useful for unraveling the dynamics of the most violent sources in the cosmos and for revealing the neutrino cross-section at extreme energy. If there exists a Greisen-Zatsepin-Kuz’min (GZK) suppression of cosmic-ray events above $E_{\mathrm{GZK}}\sim 5\times {10}^{19}\mathrm{eV}$, as predicted by theory, then the only messengers of energies beyond $E_{\mathrm{GZK}}$ are neutrinos. Cosmic neutrino fluxes can initiate air-showers through interaction in the atmosphere, or in the Earth. Neutrino trajectories will be downgoing to nearly horizontal in the former case, and “Earth-skimming” in the latter case. Thus it is important to know the acceptances (event rate/flux) of proposed air-shower experiments for detecting both types of neutrino-initiated events. We calculate these acceptances for fluorescence detectors, both space-based as with the EUSO and OWL proposals, and ground-based, as with Auger, HiRes and Telescope Array. The neutrino cross-section ${\sigma }_{\nu N}^{\mathrm{CC}}$ is unknown at energies above $5.2\times {10}^{13}\mathrm{eV}$. Although the popular QCD extrapolation of lower-energy physics offers the cross-section value of $0.54\times {10}^{-31}(E_{\nu }/{10}^{20}\mathrm{eV}{)}^{0.36}{\mathrm{cm}}^2$, new physics could raise or lower this value. Therefore, we present the acceptances of horizontal (HAS) and upgoing (UAS) air-showers as a function of ${\sigma }_{\nu N}^{\mathrm{CC}}$ over the range ${10}^{-34}$ to ${10}^{-30}{\mathrm{cm}}^2$. The dependences of acceptances on neutrino energy, shower-threshold energy, shower length, and shower column density are also studied. We introduce a cloud layer, and study its effect on rates as viewed from space and from the ground. For UAS, we present acceptances for events over land (rock), and over the ocean (water). Acceptances over water are larger by about an order of magnitude, thus favoring space-based detectors. We revisit the idea of Kusenko and Weiler [Phys. Rev. Lett. 88, 161101 (2002)] to infer ${\sigma }_{\nu N}^{\mathrm{CC}}$ at $E_{\nu }\gtrsim {10}^{20}$ from the ratio of HAS-to-UAS events, and obtain favorable results. Included in our UAS calculations are realistic energy-losses for taus, and Earth-curvature effects. Most of our calculation is analytic, allowing insight into the various subprocesses that collectively turn an incident neutrino into an observable shower.

Neutrino oscillations have established that neutrinos ${\nu }_i$ have very small masses. Theoretically, they are believed to arise through the famous seesaw mechanism from their very heavy and unobservable Dirac mass partners $N_i$. It is proposed here in a new minimal extension of the standard model with a second scalar doublet (${\eta }^{+}$, ${\eta }^0$) that the seesaw mechanism is actually radiative, and that $N_i$ and (${\eta }^{+}$, ${\eta }^0$) are experimentally observable at the forthcoming Large Hadron Collider, with the bonus that the lightest of them is also an excellent candidate for the dark matter of the Universe.

We systematically study the extension of the supersymmetric standard model (SSM) by an anomaly-free discrete gauge symmetry ${\mathit{Z}}_N$. We extend the work of Ibáñez and Ross with $N=2$, 3 to arbitrary values of $N$. As new fundamental symmetries, we find four ${\mathit{Z}}_6$, nine ${\mathit{Z}}_9$, and nine ${\mathit{Z}}_{18}$. We then place three phenomenological demands upon the low-energy effective SSM: (i) the presence of the $\mu$ term in the superpotential, (ii) baryon-number conservation up to dimension-five operators, and (iii) the presence of the seesaw neutrino mass term $L{H}_{u}L{H}_u$. We are then left with only two anomaly-free discrete gauge symmetries: baryon triality, ${\mathit{B}}_3$, and a new ${\mathit{Z}}_6$, which we call proton hexality, ${\mathit{P}}_6$. Unlike ${\mathit{B}}_3$, ${\mathit{P}}_6$ prohibits the dimension-four lepton-number violating operators. This we propose as the discrete gauge symmetry of the minimal SSM, instead of $R$ parity.

We study the question of whether or not QCD predicts a pentaquark state ${\Theta }^{+}$. We use the improved, fixed point lattice QCD action which has very little sensitivity to the lattice spacing and also allows us to reach light quark masses. The analysis was performed on a single volume of size $(1.8\mathrm{fm}{)}^3\times 3.6\mathrm{fm}$ with lattice spacing of $a=0.102\mathrm{fm}$. We use the correlation matrix method to identify the ground and excited states in the isospin 0, negative parity channel. In the quenched approximation where dynamical quark effects are omitted, we do not find any evidence for a pentaquark resonance in QCD.

Numerical simulations of full QCD on anisotropic lattices provide a convenient way to study QCD thermodynamics with fixed physics scales and reduced lattice spacing errors. We report results from calculations with two flavors of dynamical staggered fermions, where all bare parameters and the renormalized anisotropy are kept constant and the temperature is changed in small steps by varying only the number of time slices. Including results from zero-temperature scale-setting simulations, which determine the Karsch coefficients, allows for the calculation of the equation of state at finite temperatures.

There are two apparent puzzles connected with the two-body and three-body doubly charmed baryonic $B$ decays. First, earlier calculations based on QCD sum rules or the diquark model predict $\mathcal{B}({\overline{B}}^0\to {\Xi }_c^{+}{\overline{\Lambda }}_c^{-})\approx \mathcal{B}({\overline{B}}^0\to {\mathcal{B}}_c\overline{N})$, while experimentally the former has a rate 2 orders of magnitude larger than the latter. Second, a naive estimate of the branching ratio $\mathcal{O}({10}^{-9})$ for the color-suppressed three-body decay $\overline{B}\to {\Lambda }_c^{+}{\overline{\Lambda }}_c^{-}K$, which is highly suppressed by phase space, is too small by 5 to 6 orders of magnitude compared to the experiment. We show that the great suppression for the ${\Lambda }_c^{+}{\overline{\Lambda }}_c^{-}K$ production can be alleviated provided that there exists a narrow hidden charm bound state with a mass near the ${\Lambda }_c{\overline{\Lambda }}_c$ threshold. This new state that couples strongly to the charmed baryon pair can be searched for in $B$ decays and in $p\overline{p}$ collisions by studying the mass spectrum of $D^{(*)}{\overline{D}}^{(*)}$ or ${\Lambda }_c{\overline{\Lambda }}_c$. The doubly charmful decay $\overline{B}\to {\Xi }_c{\overline{\Lambda }}_c$ has a configuration more favorable than the singly charmful one such as ${\overline{B}}^0\to {\Lambda }_c\overline{p}$ since no hard gluon is needed to produce the energetic ${\Xi }_c{\overline{\Lambda }}_c$ pair in the former decay, while two hard gluons are needed for the latter process. Assuming that a soft $q\overline{q}$ quark pair is produced through the $\sigma$ and $\pi$ meson exchanges in the configuration for $\overline{B}\to {\Xi }_c{\overline{\Lambda }}_c$, it is found that its branching ratio is of order ${10}^{-3}$, in agreement with the experiment.

We study the exclusive production of $\pi \pi$ and $\rho \pi$ in hard ${\gamma }^{*}\gamma$ scattering in the forward kinematical region where the virtuality of one photon provides us with a hard scale in the process. The newly introduced concept of Transition Distribution Amplitudes (TDA) is used to perform a QCD calculation of these reactions thanks to two simple models for TDAs. Cross sections for $\rho \pi$ and $\pi \pi$ production are evaluated and compared to the possible background from the Bremsstrahlung process. This picture may be tested at intense electron-positron colliders such as CLEO and $B$ factories. The cross section $e\gamma \to e^{\prime }{\pi }^0{\pi }^0$ is finally shown to provide a possible determination of the ${\pi }^0$ axial form factor, $F_A^{{\pi }^0}$, at small $t$, which seems not to be measurable elsewhere.

We consider a Super-$\mathrm{NO}\nu \mathrm{A}$-like experimental configuration based on the use of two detectors in a long-baseline experiment as $\mathrm{NO}\nu \mathrm{A}$. We take the far detector as in the present $\mathrm{NO}\nu \mathrm{A}$ proposal and add a second detector at a shorter baseline. The location of the second off-axis detector is chosen such that the ratio $L/E$ is the same for both detectors, being $L$ the baseline and $E$ the neutrino energy. We consider liquid argon and water-Čerenkov techniques for the second off-axis detector and study, for different experimental setups, the detector mass required for the determination of the neutrino mass hierarchy, for different values of ${\theta }_{13}$. We also study the capabilities of such an experimental setup for determining $CP$-violation in the neutrino sector. Our results show that by adding a second off-axis detector a remarkable enhancement on the capabilities of the current $\mathrm{NO}\nu \mathrm{A}$ experiment could be achieved.

In our previous work of [K. Farakos and P. Pasipoularides, Phys. Lett. B 621, 224 (2005).] we studied the stability of the RS2 model with a nonminimally coupled bulk scalar field $\varphi$, and we found that in appropriate regions of $\xi$ the standard RS2 vacuum becomes unstable. The question that arises is whether there exists other new static stable solutions where the system can relax. In this work, by solving numerically the Einstein equations with the appropriate boundary conditions on the brane, we find that depending on the value of the nonminimal coupling $\xi$, this model possesses three classes of new static solutions with different characteristics. We also examine what happens when the fine-tuning of the RS2 model is violated, and we obtain that these three classes of solutions are preserved in appropriate regions of the parameter space of the problem. The stability properties and possible physical implications of these new solutions are discussed in the main part of this paper. Especially in the case where $\xi ={\xi }_c$ (${\xi }_c$ is the five-dimensional conformal coupling) and the fine-tuning is violated, we obtain a physically interesting static stable solution.

We argue that too much exotic scene setting is not necessary for the explanation of the Centauro events observed by the mountain based emulsion chambers. We show that a proper understanding of the detector helps to find a mundane solution to the “decades old cosmic ray mystery.” We conclude that the exotic events observed so far are not inconsistent with the incorrect evaluation of the detector response and misinterpretation of the experimental signal.

Quark propagators of the unquenched Kogut-Susskind (KS) fermion obtained from the gauge configurations of the MILC Collaboration are measured after Landau gauge fixing and using the $\mathrm{\text{Staple}}+\mathrm{\text{Naik}}$ action. Presence of the $\overline{q}q$ condensates and $A^2$ condensates in the dynamical mass $M(q)$ and the quark wave function renormalization $Z_{\psi }(q^2)$ are investigated. We obtain the correlation of the renormalization factor of the running coupling taken at $\mu \sim 6\mathrm{GeV}$ and that of the quark wave function renormalization $Z_{\psi }(q^2)$ of the $\mathrm{\text{Staple}}+\mathrm{\text{Naik}}$ action. The mass function $M(q)$ is finite at $q=0$ and its chiral limit is $\sim 0.38\mathrm{GeV}$. We compared the results corrected by the scale of the vertex renormalization and the tadpole renormalization with the corresponding values obtained by the Asqtad action without renormalization and observed good agreement. Implication of infrared finite $Z_2(q)=1/Z_{\psi }(q^2)$ to the Kugo-Ojima confinement criterion is discussed.

The simultaneous investigation of the pion electromagnetic form factor in the space- and timelike regions within a light-front model allows one to address the issue of nonvalence components of the pion and photon wave functions. Our relativistic approach is based on a microscopic vector-meson-dominance model for the dressed vertex where a photon decays in a quark-antiquark pair, and on a simple parametrization for the emission or absorption of a pion by a quark. The results show an excellent agreement in the space like region up to $-10(\mathrm{GeV}/c{)}^2$, while in timelike region the model produces reasonable results up to $10(\mathrm{GeV}/c{)}^2$.