We study the modified theory of gravity in the Friedmann-Robertson-Walker universe composed of several perfect fluids. We consider the power law inflation and determine the equation of state parameters in terms of the parameters of modified gravity’s Lagrangian in the early universe. We also briefly discuss the gravitational baryogenesis in this model.

In the physics of flavor mixing, the flavor states are given by superpositions of mass eigenstates. By using the occupation number to define a multiqubit space, the flavor states can be interpreted as multipartite mode-entangled states. By exploiting a suitable global measure of entanglement, based on the entropies related to all possible bipartitions of the system, we analyze the correlation properties of such states in the instances of three- and four-flavor mixing. Depending on the mixing parameters, and, in particular, on the values taken by the free phases, responsible for the $CP$-violation, entanglement concentrates in certain bipartitions. We quantify in detail the amount and the distribution of entanglement in the physically relevant cases of flavor mixing in quark and neutrino systems. By using the wave packet description for localized particles, we use the global measure of entanglement, suitably adapted for the instance of multipartite mixed states, to analyze the decoherence, induced by the free evolution dynamics, on the quantum correlations of stationary neutrino beams. We define a decoherence length as the distance associated with the vanishing of the coherent interference effects among massive neutrino states. We investigate the role of the $CP$-violating phase in the decoherence process.

We use QCD sum rule approach to calculate the masses of the ground-state ${\Lambda }_Q$ and ${\Sigma }_Q^{(*)}$ baryons. Contributions of the operators up to dimension six are included in operator product expansion. The resulting heavy baryonic masses from the calculations are $m_{{\Lambda }_b}=5.69\pm 0.13\mathrm{GeV}$, and $m_{{\Lambda }_c}=2.31\pm 0.19\mathrm{GeV}$ for ${\Lambda }_Q$; $m_{{\Sigma }_b}=5.73\pm 0.21\mathrm{GeV}$, $m_{{\Sigma }_b^{*}}=5.81\pm 0.19\mathrm{GeV}$, $m_{{\Sigma }_c}=2.40\pm 0.31\mathrm{GeV}$ and $m_{{\Sigma }_c^{*}}=2.56\pm 0.24\mathrm{GeV}$ for ${\Sigma }_Q^{(*)}$, respectively, which are in good agreement with the experimental values.

We study decoherence models for flavor oscillations in four-dimensional stochastically fluctuating space-times and discuss briefly the sensitivity of current neutrino experiments to such models. We demonstrate the model dependence of the associated decoherence-induced damping coefficients in front of the oscillatory terms in the respective transition probabilities between flavors. Within the context of specific models of foam, involving pointlike D-branes and leading to decoherence-induced damping which is inversely proportional to the neutrino energies, we also argue that future limits on the relevant decoherence parameters coming from TeV astrophysical neutrinos, to be observed in ICE-CUBE, are not far from theoretically expected values with Planck-mass suppression. Ultrahigh energy neutrinos from gamma ray bursts at cosmological distances can also exhibit in principle sensitivity to such effects.

Recently, the laser experiments BMV and GammeV, searching for light shining through walls, have published data and calculated new limits on the allowed masses and couplings for axionlike particles. In this paper we point out that these experiments can serve to constrain a much wider variety of hidden-sector particles such as, e.g., minicharged particles and hidden-sector photons. The new experiments improve the existing bounds from the older BFRT experiment by a factor of 2. Moreover, we use the new PVLAS constraints on a possible rotation and ellipticity of light after it has passed through a strong magnetic field to constrain pure minicharged particle models. For masses $\lesssim 0.05\mathrm{eV}$, the charge is now restricted to be less than $(3-4)\times {10}^{-7}$ times the electron electric charge. This is the best laboratory bound and comparable to bounds inferred from the energy spectrum of the cosmic microwave background.

We perform an analysis of transverse-momentum dependent parton-distribution functions, making use of their renormalization properties in terms of their leading-order anomalous dimensions. We show that the appropriate Wilson line in the light cone gauge, associated with such quantities, is a cusped one at light cone infinity. To cancel the ensuing cusp anomalous dimension, we include in the definition of the transverse-momentum dependent parton-distribution functions an additional soft counter term (gauge link) along that cusped transverse contour. We demonstrate that this is tantamount to an “intrinsic (Coulomb) phase,” which accumulates the full gauge history of the color-charged particle.

We study baryons in $SU(N)$ gauge theories, according to the gauge/string correspondence based on IIB string theory. The $D5$-brane, in which $N$ fundamental strings are dissolved as a color singlet, is introduced as the baryon vertex, and its configurations are studied. We find a point- and split-type of vertex. In the latter case, two cusps appears, and they are connected by a flux composed of dissolved fundamental strings with a definite tension. In both cases, $N$ fundamental quarks are attached on the cusp(s) of the vertex to cancel the surface term. In the confining phase, we find that the quarks in the baryon feel the potential increasing linearly with the distance from the vertex. At finite temperature and in the deconfining phase, we find stable $k$-quark “baryons”, which are constructed of an arbitrary number of $k(<N)$ quarks.

In a recent paper, we proposed the possibility that supersymmetry breaking is communicated dominantly via a $U(1{)}^{\prime }$ vector multiplet. We also required that the $U(1{)}^{\prime }$ plays a crucial role in solving the $\mu$ problem. We discuss here in detail both the construction and the phenomenology of one class of such models. The low-energy spectrum generically contains heavy sfermions, Higgsinos and exotics $\sim 10–100\mathrm{TeV}$; an intermediate $M_{Z^{\prime }}$ $\sim 3–30\mathrm{TeV}$; light gauginos $\sim 100–1000\mathrm{GeV}$, of which the lightest can be $W$-ino-like; a light Higgs with a mass of $\sim 140\mathrm{GeV}$; and a singlino which can be very light. We present a set of possible consistent charge choices. Several benchmark models are used to demonstrate characteristic phenomenological features. Special attention is devoted to interesting LHC (Large Hadron Collider) signatures such as gluino decay and the decay patterns of the electroweak-inos. Implications for neutrino masses, exotic decays, $R$-parity, gauge unification, and the gravitino mass are briefly discussed.

The standard model extension with additional Lorentz violating terms allows for redefining the equation of motion of a propagating left-handed fermionic particle. The obtained Dirac-type equation can be embedded in a generalized Lorentz-invariance-preserving algebra through the definition of Lorentz algebralike generators with a lightlike preferred axis. The resulting modification to the fermionic equation of motion introduces some novel ingredients to the phenomenological analysis of the cross section of the tritium $\beta$ decay. Assuming lepton number conservation, our formalism provides a natural explanation for the tritium $\beta$-decay end point via an effective neutrino mass term without the need of a sterile right-handed state.

An $SU(5)$ grand unification scheme for effective $3+1$-dimensional fields dynamically localized on a domain-wall brane is constructed. This is achieved through the confluence of the clash-of-symmetries mechanism for symmetry breaking through domain-wall formation, and the Dvali-Shifman gauge-boson localization idea. It requires an $E_6$ gauge-invariant action, yielding a domain-wall solution that has $E_6$ broken to differently embedded $SO(10)\otimes U(1)$ subgroups in the two bulk regions on opposite sides of the wall. On the wall itself, the unbroken symmetry is the intersection of the two bulk subgroups, and contains $SU(5)$. A $4+1$-dimensional fermion family in the 27 of $E_6$ gives rise to localized left-handed zero modes in the $5^{*}\oplus 10\oplus 1\oplus 1$ representation of $SU(5)$. The remaining ten fermion components of the 27 are delocalized exotic states, not appearing in the effective $3+1$-dimensional theory on the domain-wall brane. The scheme is compatible with the type-2 Randall-Sundrum mechanism for graviton localization; the single extra dimension is infinite.

We study the physics at finite nuclear density in the framework of the AdS/QCD model with a holographic baryon field included. Based on a mean field type approach, we introduce the nucleon density as a bi-fermion condensate of the lowest mode of the baryon field and calculate the density dependence of the chiral condensate and the nucleon mass. We observe that the chiral condensate as well as the mass of nucleon decrease with increasing nuclear density. The resulting density dependence is, however, much weaker than those obtained in earlier studies based on other QCD effective theories. We also consider the mass splitting of charged vector mesons in isospin asymmetric nuclear matter.

We study the effects that the gravitational interaction of $f(R)$ theories of gravity in Palatini formalism has on the stationary states of the hydrogen atom. We show that the role of gravity in this system is very important for Lagrangians $f(R)$ with terms that grow at low curvatures, which have been proposed to explain the accelerated expansion rate of the universe. In fact, new gravitationally induced terms in the atomic Hamiltonian generate a strong backreaction that is incompatible with the very existence of bound states. In fact, in the $1/R$ model, hydrogen disintegrates in less than two hours. The universe that we observe is, therefore, incompatible with that kind of gravitational interaction. Lagrangians with high curvature corrections do not lead to such instabilities.

Upcoming precision measurements of the temperature anisotropy of the cosmic microwave background at high multipoles will need to be complemented by a more complete understanding of recombination, which determines the damping of anisotropies on these scales. This is the third in a series of papers describing an accurate theory of He i and He ii recombination. Here we describe the effect of Thomson scattering, the ${}^3\mathrm{He}$ isotope shift, the contribution of rare decays, collisional processes, and peculiar motion. These effects are found to be negligible: Thomson and ${}^3\mathrm{He}$ scattering modify the free electron fraction $x_e$ at the level of $\mathrm{\text{several}}\times {10}^{-4}$. The uncertainty in the $2^3{P}^o-1^{1}S$ rate is significant, and for conservative estimates, gives uncertainties in $x_e$ of order ${10}^{-3}$. We describe several convergence tests for the atomic level code and its inputs, derive an overall $C_{\ell }$ error budget, and relate shifts in $x_e(z)$ to the changes in $C_{\ell }$, which are at the level of 0.5% at $\ell =3000$. Finally, we summarize the main corrections developed thus far. The remaining uncertainty from known effects is $\sim 0.3\%$ in $x_e$.

Interpretation of precision measurements of the cosmic microwave background (CMB) will require a detailed understanding of the recombination era, which determines such quantities as the acoustic oscillation scale and the Silk damping scale. This paper is the second in a series devoted to the subject of helium recombination, with a focus on two-photon processes in He i. The standard treatment of these processes includes only the spontaneous two-photon decay from the $2^{1}S$ level. We extend this treatment by including five additional effects, some of which have been suggested in recent papers but whose impact on He i recombination has not been fully quantified. These are: (i) stimulated two-photon decays; (ii) two-photon absorption of redshifted He i line radiation; (iii) two-photon decays from highly excited levels in He i ($n^{1}S$ and $n^{1}D$, with $n\ge 3$); (iv) Raman scattering; and (v) the finite width of the $2^1{P}^o$ resonance. We find that effect (iii) is highly suppressed when one takes into account destructive interference between different intermediate states contributing to the two-photon decay amplitude. Overall, these effects are found to be insignificant: they modify the recombination history at the level of several parts in ${10}^4$.

Precision measurements of the cosmic microwave background temperature anisotropy on scales $\ell >500$ will be available in the near future. Successful interpretation of these data is dependent on a detailed understanding of the damping tail and cosmological recombination of both hydrogen and helium. This paper and two companion papers are devoted to a precise calculation of helium recombination. We discuss several aspects of the standard recombination picture, and then include feedback, radiative transfer in He i lines with partial redistribution, and continuum opacity from H i photoionization. In agreement with past calculations, we find that He ii recombination proceeds in Saha equilibrium, whereas He i recombination is delayed relative to Saha due to the low rates connecting excited states of He i to the ground state. However, we find that at $z<2200$ the continuum absorption by the rapidly increasing H i population becomes effective at destroying photons in the He i $2^1{P}^o-1^{1}S$ line, causing He i recombination to finish around $z\approx 1800$, much earlier than previously estimated.

High precision planet orbital data extracted from direct observation, spacecraft explorations, and laser ranging techniques enable to constrain the maximal dark matter density of a spherical halo centered around the Sun. If we assume a halo profile with a power-law dependence in the heliocentric distance, the maximal density at Earth’s location is of the order ${10}^5\mathrm{GeV}/{\mathrm{cm}}^3$. Moreover, this value shows only a mild dependence on the slope of the halo profile, taken between 0 and $-2$. This bound competes with that obtained from the perihelion precession limits.

A supersymmetric extension of the standard model based on the discrete $Q_6$ family symmetry is considered, and we investigate flavor changing neutral current (FCNC) processes, especially those mediated by heavy flavor changing neutral Higgs bosons. Because of the family symmetry the number of the independent Yukawa couplings is smaller than that of the observed quantities such as the Cabibbo-Kobayashi-Maskawa matrix and the quark masses, so that the FCNCs can be parametrized only by the mixing angles and masses of the Higgs fields. We focus our attention on the mass differences of the neutral $K$, $D$, and $B$ mesons. All the constraints including that from the ratio $\Delta M_{B_s}/\Delta M_{B_d}$ can be satisfied, if the heavy Higgs bosons are heavier than $\sim 1.5\mathrm{TeV}$. If the constraint from $\Delta M_K$ is slightly relaxed, the heavy Higgs bosons can be as light as $\sim 0.4\mathrm{TeV}$, which is within the accessible range of LHC.

We have investigated the effects of unparticles in decays $B\to l\nu$. It is found that the direct $CP$ violation in the decays, which is zero in the standard model, can show up due to the $CP$ conserving phase intrinsic in unparticle physics. For $l=\tau$, the direct $CP$ asymmetry can reach 30% for the scalar unparticle contribution, and 100% for the longitudinal vector unparticle contribution under the constraints of $\mathrm{Br}(B\to \tau \nu )$ and $\nu e$ elastic scattering. If both unparticle-lepton coupling universality and unparticle-quark coupling universality are assumed the constraint from $\mathrm{Br}(\pi \to \mu \nu )$ leads that the direct $CP$ violation in $B\to l\nu$ can only reach at most 8% and 1% for scalar and vector unparticle contributions, respectively, if $d_{\mathcal{U}}<2$. If the direct $CP$ violation is observed in the future it would give strong evidence for the existence of unparticle stuff.

The amplitude for the production of a single photon associated with a quark pair in the fusion of two off-shell gluons is calculated. The matrix element found is applied to the inclusive prompt photon hadroproduction at high energies in the framework of the $k_T$-factorization QCD approach. The total and differential cross sections are calculated in both central and forward pseudorapidity regions. The conservative error analysis is performed. We used the unintegrated gluon distributions in a proton which were obtained from the full Catani-Ciafaloni-Fiorani-Marchesini (CCFM) evolution equation as well as from the Kimber-Martin-Ryskin prescription. Theoretical results were compared with recent experimental data taken by the D0 and CDF collaborations at Fermilab Tevatron. Theoretical predictions for the LHC energies are given.