We compute the $\mathcal{O}(g^2)$ contribution to the thermodynamic pressure for Wilson fermions in the standard, the twisted mass, and the clover improved formulation in lattice perturbation theory, including finite mass effects. We compare the continuum approaches of these discretizations for the massive ideal and interacting gas. In all cases, for $N_{\tau }\ge 8$ cutoff effects of Wilson-type fermions are comparable to those of staggered fermions, but asymptotic scaling requires $N_{\tau }>10$.

We propose an ansatz for the nonperturbative beta-function of a generic nonsupersymmetric Yang-Mills theory with or without fermions in an arbitrary representation of the gauge group. While our construction is similar to the recently proposed Ryttov-Sannino all-order beta-function, the essential difference is that it allows for the existence of an unstable ultraviolet fixed point in addition to the predicted Banks-Zaks–like infrared stable fixed point. Our beta-function preserves all of the tested features with respect to the nonsupersymmetric Yang-Mills theories. We predict the conformal window identifying the lower end of it as a merger of the infrared and ultraviolet fixed points.

We present a class of warped extra dimensional models whose flavor violating interactions are much suppressed compared to the usual anarchic case due to flavor alignment. Such suppression can be achieved in models where part of the global flavor symmetry is gauged in the bulk and broken in a controlled manner. We show that the bulk masses can be aligned with the down-type Yukawa couplings by an appropriate choice of bulk flavon field representations and TeV brane dynamics. This alignment could reduce the flavor violating effects to levels that allow for a Kaluza-Klein scale as low as 2–3 TeV, making the model observable at the LHC. However, the up-type Yukawa couplings on the IR brane, which are bounded from below by recent bounds on $CP$ violation in the $D$ system, induce flavor misalignment radiatively. Off-diagonal down-type Yukawa couplings and kinetic mixings for the down quarks are both consequences of this effect. These radiative Yukawa corrections can be reduced by raising the flavon vacuum expectation value on the IR brane (at the price of some moderate tuning), or by extending the Higgs sector. The flavor changing effects from the radiatively induced Yukawa mixing terms are at around the current upper experimental bounds. We also show the generic bounds on UV-brane induced flavor violating effects, and comment on possible additional flavor violations from bulk flavor gauge bosons and the bulk Yukawa scalars.

The annihilation rate of dark matter particles plays a crucial role in dark matter studies, for it determines their relic density and their indirect detection signal. In this paper, we show that this annihilation rate can receive large additional contributions from three-body final states consisting of a real and a virtual massive particle, such as $W{W}^{*}(\to Wf{\overline{f}}^{\prime })$ and $t{\overline{t}}^{*}(\to tW\overline{b})$. We consider two specific examples, from the singlet model and the minimal supersymmetric standard model, and find that, due to the new three-body final state contributions, the prediction for the relic density may decrease by more than a factor two, whereas the present dark matter annihilation rate gets enhanced by up to 2 orders of magnitude. Some of the implications of these results are briefly discussed.

Leading and subleading-twist transverse momentum dependent parton distribution functions (TMDs) are studied in a quark-model framework provided by the bag model. A complete set of relations among different TMDs is derived, and the question is discussed how model (in)dependent such relations are. A connection of the pretzelosity distribution and quark orbital angular momentum is derived. Numerical results are presented, and applications for phenomenology are discussed. In particular, it is shown that in the valence-$x$ region the bag model supports a Gaussian Ansatz for the transverse momentum dependence of TMDs.

The present work generalizes a nonlocal version of the Polyakov-loop-extended Nambu and Jona-Lasinio (PNJL) model to the case of three active quark flavors, with inclusion of the axial U(1) anomaly. Gluon dynamics is incorporated through a gluonic background field, expressed in terms of the Polyakov loop. The thermodynamics of the nonlocal PNJL model accounts for both chiral and deconfinement transitions. Our results obtained in mean-field approximation are compared to lattice QCD results for $N_f=2+1$ quark flavors. Additional pionic and kaonic contributions to the pressure are calculated in random phase approximation. Finally, this nonlocal three-flavor PNJL model is applied to the finite density region of the QCD phase diagram. It is confirmed that the existence and location of a critical point in this phase diagram depend sensitively on the strength of the axial U(1) breaking interaction.

Pion exchange in S-wave between hadrons that are themselves in a relative S-wave is shown to shift energies by hundreds of MeV, leading to deeply bound quasimolecular states. In the case of charmed mesons $D^{*}$, $D_1$ a spectroscopy arises consistent with enigmatic charmonium states observed above 4 GeV in $e^{+}{e}^{-}$ annihilation. A possible explanation of $Y(4260)\to \psi \pi \pi$ and $Y(4360)\to {\psi }^{\prime }\pi \pi$ is found. We give results for all isospin and charge-conjugation combinations, and comment on flavor exotic doubly charmed states and bottomonium analogs. A search in $D\overline{D}3\pi$ is recommended to test this hypothesis. An exotic $1^{-+}$ is predicted to occur in the vicinity of the $Y(4260)$.

The first dedicated search for the rare neutral-kaon decay $K_L^0\to {\pi }^0\nu \overline{\nu }$ has been carried out in the E391a experiment at the KEK 12-GeV proton synchrotron. The final upper limit of $2.6\times {10}^{-8}$ at the 90% confidence level was set on the branching ratio for the decay.

The time evolution of collective modes in an expanding ultrarelativistic and (effectively) Abelian plasma is studied in the hard-loop approximation semianalytically by means of integrodifferential equations. A previous treatment is generalized to arbitrary orientation of wave vectors with respect to the direction of anisotropy and thus to a fully $3+1$ dimensional situation. Moreover, initial fluctuations are allowed in both gauge fields and currents, which is necessary in the case of (stable) longitudinal modes. For unstable (Weibel) modes, this generalization of initial conditions reduces drastically the lower bound on the delay in the onset of growth that was found previously by considering only collective gauge fields as seeds. This makes it appear much more likely that non-Abelian plasma instabilities seeded by small initial rapidity fluctuations could play an important role in the early stage of heavy-ion collisions at LHC energies.

We study the one-loop renormalization of high-energy Lorentz-violating four-fermion models. We derive general formulas and then consider a number of specific models. We study the conditions for asymptotic freedom and give a practical method to determine the asymptotic-freedom domain. We also point out that in some models the renormalization-group flow contains rational Zimmermann trajectories that might hide new symmetries.

We study a QED extension that is unitary, $CPT$ invariant, and super-renormalizable, but violates Lorentz symmetry at high energies, and contains higher-dimension operators (LVQED). Divergent diagrams are only one- and two-loop. We compute the one-loop renormalizations at high and low energies and analyze the relation between them. It emerges that the powerlike divergences of the low-energy theory are multiplied by arbitrary constants, inherited by the high-energy theory, and therefore can be set to zero at no cost, bypassing the hierarchy problem.

Deformed special relativity (DSR) is obtained by imposing a maximal energy to special relativity and deforming the Lorentz symmetry (more exactly, the Poincaré symmetry) to accommodate this requirement. One can apply the same procedure in the context of Galilean relativity by imposing a maximal speed (the speed of light). Effectively, one deforms the Galilean group and this leads to a noncommutative space structure, together with the deformations of composition of speed and conservation of energy momentum. In doing so, one runs into most of the ambiguities that one stumbles onto in the DSR context. However, this time, special relativity is there to tell us what is the underlying physics, in such a way we can understand and interpret these ambiguities. We use these insights to comment on the physics of DSR.

Effective theories are nonlocal at the scale of the eliminated heavy particles modes. The gradient expansion, which represents such nonlocality, must be truncated to have treatable models. This step leads to the proliferation of the degrees of freedom, which renders the identification of the states of the effective theory nontrivial. Furthermore, it generates nondefinite metric in the Fock space, which in turn endangers the unitarity of the effective theory. It is shown that imposing a generalized Kubo-Martin-Schwinger boundary conditions for the new degrees of freedom leads to reflection positivity for a wide class of Euclidean effective theories, thereby these lead to acceptable theories when extended to real-time.

The quantum gravity framework motivates us to find new theories in which an observer-independent finite energy upper bound (preferably Planck energy) exists. We have studied the modifications in the thermodynamical properties of a photon gas in such a scenario where we have an invariant energy scale. We show that the density of states and the entropy in such a framework are less than the corresponding quantities in Einstein’s special relativity theory. This result can be interpreted as a consequence of the deformed Lorentz symmetry present in the particular model we have considered.

We study cosmological consequences of the noncommutative approach to the standard model of particle physics. Neglecting the nonminimal coupling of the Higgs field to the curvature, noncommutative corrections to Einstein’s equations are present only for inhomogeneous and anisotropic space-times. Considering the nonminimal coupling however, corrections are obtained even for background cosmologies. Links with dilatonic gravity as well as chameleon cosmology are briefly discussed, and potential experimental consequences are mentioned.

We investigate the possibility that the behavior of the rotational velocities of test particles gravitating around galaxies can be explained in the framework of modified gravity models with nonminimal matter-geometry coupling. Generally, the dynamics of test particles around galaxies, as well as the corresponding mass deficit, is explained by postulating the existence of dark matter. The extra terms in the gravitational field equations with geometry-matter coupling modify the equations of motion of test particles and induce a supplementary gravitational interaction. Starting from the variational principle describing the particle motion in the presence of the nonminimal coupling, the expression of the tangential velocity of a test particle, moving in the vacuum on a stable circular orbit in a spherically symmetric geometry, is derived. The tangential velocity depends on the metric tensor components, as well as on the coupling function between matter and geometry. The Doppler velocity shifts are also obtained in terms of the coupling function. If the tangential velocity profile is known, the coupling term between matter and geometry can be obtained explicitly in an analytical form. The functional form of this function is obtained in two cases, for a constant tangential velocity and for an empirical velocity profile obtained from astronomical observations, respectively. All the physical and geometrical quantities in the modified gravity model with nonminimal coupling between matter and geometry can be expressed in terms of observable/measurable parameters, like the tangential velocity, the baryonic mass of the galaxy, and the Doppler frequency shifts. Therefore, these results open the possibility of directly testing the modified gravity models with nonminimal coupling between matter and geometry by using direct astronomical and astrophysical observations at the galactic or extragalactic scale.

We study the inflation process of the Universe based on the renormalizable quantum gravity formulated as a conformal field theory. We show that the power-law conformal field theory spectrum approaches that of the Harrison-Zel’dovich-Peebles–type as the amplitude of gravitational potential gradually reduces during the inflation. The non-Gaussanity parameter is preserved within an order of unity due to the diffeomorphism invariance. Sharp falloff of the angular power spectrum of cosmic microwave background at large scale is understood as a consequence of the existence of dynamical scale of the quantum gravity ${\Lambda }_{\mathrm{QG}}(\simeq {10}^{17}\mathrm{GeV})$. The angular power spectra are computed and compared with the WMAP5 and ACBAR data with a quality of ${\chi }^2/\mathrm{dof}\simeq 1.1$.

We show that quintessence, when it is described by a tachyonic field, can amplify a tiny primordial gradient generating a preferred direction in the sky. In its simplest realization, this mechanism only affects the cosmic microwave background fluctuations at the quadrupole level. We briefly discuss how higher multipoles can also be affected, once the full structure of the quintessence potential is taken into account.

In this work we study the dynamics of the axisymmetric Bianchi-IX cosmological model with a term of quantum potential added. As it is well known, this class of Bianchi-IX models is homogeneous and anisotropic with two scale factors, $A(t)$ and $B(t)$, derived from the solution of Einstein’s equation for general relativity. The model we use in this work has a cosmological constant and the matter content is dust. To this model we add a quantum-inspired potential that is intended to represent short-range effects due to the general relativistic behavior of matter in small scales and play the role of a repulsive force near the singularity. We find that this potential restricts the dynamics of the model to positive values of $A(t)$ and $B(t)$ and alters some qualitative and quantitative characteristics of the dynamics studied previously by several authors. We make a complete analysis of the phase space of the model finding critical points, periodic orbits, stable/unstable manifolds using numerical techniques such as Poincaré section, numerical continuation of orbits, and numerical globalization of invariant manifolds. We compare the classical and the quantum models. Our main result is the existence of homoclinic crossings of the stable and unstable manifolds in the physically meaningful region of the phase space [where both $A(t)$ and $B(t)$ are positive], indicating chaotic escape to inflation and bouncing near the singularity.

We investigate magnetic monopole solutions of the non-Abelian Dirac-Born-Infeld (DBI) action describing two coincident non-BPS D9-branes in flat space. Just as in the case of kink and vortex solitonic tachyon solutions of the full DBI non-BPS actions, as previously analyzed by Sen, these monopole configurations are singular in the first instance and require regularization. We discuss a suitable non-Abelian ansatz that describes a pointlike magnetic monopole and show it solves the equations of motion to leading order in the regularization parameter. Fluctuations are studied and shown to describe a codimension three BPS D6-brane, and a formula is derived for its tension.