$n$-DBI gravity is a gravitational theory introduced in [C. Herdeiro and S. Hirano, arXiv:1109.1468.], motivated by Dirac-Born-Infeld type conformal scalar theory and designed to yield noneternal inflation spontaneously. It contains a foliation structure provided by an everywhere timelike vector field $\mathbf{n}$, which couples to the gravitational sector of the theory, but decouples in the small curvature limit. We show that any solution of Einstein gravity with a particular curvature property is a solution of $n$-DBI gravity. Among them is a class of geometries isometric to a Reissner-Nordström–(anti)-de Sitter black hole, which is obtained within the spherically symmetric solutions of $n$-DBI gravity minimally coupled to the Maxwell field. These solutions have, however, two distinct features from their Einstein gravity counterparts: (1) the cosmological constant appears as an integration constant and can be positive, negative, or vanishing, making it a variable quantity of the theory; and (2) there is a nonuniqueness of solutions with the same total mass, charge, and effective cosmological constant. Such inequivalent solutions cannot be mapped to each other by a foliation preserving diffeomorphism. Physically they are distinguished by the expansion and shear of the congruence tangent to $\mathbf{n}$, which define scalar invariants on each leaf of the foliation.

We calculate the ${}^4\mathrm{He}$ abundance in a universe of Bianchi type I whose cosmic anisotropy is dynamically generated by a fluid with anisotropic equation of state. Requiring that the relative variation of mass fraction of ${}^4\mathrm{He}$ is less than 4% with respect to the standard isotropic case to be consistent with astrophysical data, we constrain the parameter of cosmic anisotropy, the shear $\Sigma$, as $|\Sigma (T_f)|\lesssim 0.4$, where $T_f$ is the freeze-out temperature of the weak interactions that interconvert neutrons and protons. Anisotropic fluids, whose energy density is subdominant with respect to the energy content of the Universe during inflation and radiation era, generate much smaller shears at the time of freeze-out and then do not appreciably affect the standard ${}^4\mathrm{He}$ production. This is the case of anisotropic dark energy, and of a uniform magnetic field with energy density much smaller than about 1.25 times the energy density of neutrinos.

The CAH+ measure regulates the infinite spacetime volume of the multiverse by constructing a surface of constant comoving apparent horizon (CAH) and then removing the future light cones of all points on that surface (the latter prescription is referred to by the + in the name of the measure). This measure was motivated by the conjectured duality between the bulk of the multiverse and its future infinity and by the causality condition, requiring that the cutoff surfaces of the measure should be spacelike or null. Here we investigate the phenomenology of the CAH+ measure and find that it does not suffer from any known pathologies. The distribution for the cosmological constant $\Lambda$ derived from this measure is in a good agreement with the observed value, and the distribution for the number of inflationary $e$-foldings satisfies the observational constraint. The CAH+ measure does not exhibit any “runaway” behaviors at zero or negative values of Lambda, which have been recently shown to afflict a number of other measures.

We compute the contribution of phonons to the shear viscosity $\eta$ in superfluid neutron stars, assuming neutron pairing in a ${}^{1}S_0$ channel. We use a Boltzmann equation amended by a collision term that takes into account the binary collisions of phonons. We use effective field theory techniques to extract the phonon scattering rates, written as a function of the equation of state of the system. Our formulation is rather general, and can be used to extract the shear viscosity due to binary collisions of phonons for other superfluids, such as the cold Fermi gas in the unitarity limit. We find that $\eta \propto 1/T^5$, the proportionality factor depending on the equation of state of the system. Our results indicate that the phonon contribution to $\eta$ cannot be ignored and might have relevant effects in the dynamics of the different oscillation modes of the star.

We study the effect of primordial magnetic fields (PMFs) on the anisotropies of the cosmic microwave background (CMB). We assume the spectrum of PMFs is described by log-normal distribution which has a characteristic scale, rather than power-law spectrum. This scale is expected to reflect the generation mechanisms and our analysis is complementary to previous studies with power-law spectrum. We calculate power spectra of energy density and Lorentz force of the log-normal PMFs, and then calculate CMB temperature and polarization angular power spectra from scalar, vector, and tensor modes of perturbations generated from such PMFs. By comparing these spectra with WMAP7, QUaD, CBI, Boomerang, and ACBAR data sets, we find that the current CMB data set places the strongest constraint at $k\simeq {10}^{-2.5}{\mathrm{Mpc}}^{-1}$ with the upper limit $B\lesssim 3\mathrm{nG}$.

The presence of noncyclic phases is revealed in the time evolution of mixed meson systems. Such phases are related to the parameter $z$ describing the $CPT$ violation; moreover, a nonzero phase difference between particle and antiparticle arises only in the presence of $CPT$ symmetry breaking. Thus, a completely new test for the $CPT$ invariance can be provided by the study of such phases in mixed mesons. Systems which are particularly interesting for such an analysis are the $B_s^0-{\overline{B}}_s^0$ and the $K^0-{\overline{K}}^0$ ones. In order to introduce noncyclic phases, some aspects of the formalism describing the mixed neutral mesons are analyzed. Since the effective Hamiltonian of systems like $K^0-{\overline{K}}^0$, $B^0-{\overline{B}}^0$, $B_s^0-{\overline{B}}_s^0$, $D^0-{\overline{D}}^0$ is non-Hermitian and non-normal, it is necessary to diagonalize it by utilizing the rules of non-Hermitian quantum mechanics.

We study an extension of the minimal supersymmetric standard model (MSSM) which includes both new $SU(2)$ triplets with hypercharge $\pm 1$ and a standard model gauge singlet (à la the next-to-minimal supersymmetric standard model [NMSSM]) which are coupled to each other. We are motivated by the little hierarchy problem, as well as by the $\mu$ problem of the MSSM. We show that the NMSSM and the triplet-extended MSSM can successfully solve problems of one another: while triplets are responsible for large correction to the lightest physical Higgs mass, the singlet’s vacuum expectation value (VEV) explains why the $\mu$ terms (for the Higgs doublets and the new triplets) are naturally of order the electroweak (EW) scale. We also show that singlet-triplet coupling significantly changes the renormalization group evolution of the singlet mass squared, helping to render this mass squared negative, as required for the singlet to acquire a VEV. We analyze constraints on this scenario from EW precision measurements and find that a relatively large region of the parameter space of this model is viable, especially with the triplet fermions (including doubly charged) being light.

We discuss neutrino masses from higher than $d=5$ effective operators in a supersymmetric framework, where we explicitly demonstrate which operators could be the leading contribution to neutrino mass in the minimal supersymmetric standard model and next to minimal supersymmetric standard model. As an example, we focus on the $d=7$ operator $LL{H}_u{H}_u{H}_d{H}_u$, for which we systematically derive all tree-level decompositions. We argue that many of these lead to a linear or inverse seesaw scenario with two extra neutral fermions, where the lepton number violating term is naturally suppressed by a heavy mass scale when the extra mediators are integrated out. We choose one example, for which we discuss possible implementations of the neutrino flavor structure. In addition, we show that the heavy mediators, in this case $SU(2)$ doublet fermions, may indeed be observable at the LHC, since they can be produced by Drell-Yan processes and lead to displaced vertices when they decay. However, the direct observation of lepton number violating processes is on the edge at LHC.

We study radion phenomenology in an warped extra-dimension scenario with standard model fields in the bulk, with and without an additional fourth family of fermions. The radion couplings with the fermions will be generically misaligned with respect to the standard model fermion mass matrices, therefore producing some amount of flavor-violating couplings and potentially influencing production and decay rates of the radion. Simple analytic expressions for the radion-fermion couplings are obtained with three or four families. We also update and analyze the current experimental limits on radion couplings and on the model parameters, again with both three- and four-family scenarios. We finally present the modified decay branching ratios of the radion with an emphasis on the new channels involving flavor-diagonal and flavor-violating decays into fourth-generation quarks and leptons.

We present a new calculation of the $D\to \pi$, $l\nu$ semileptonic form factor $f_{+}^{D\to \pi }(q^2)$ at $q^2=0$ based on “highly improved staggered quark” charm and light valence quarks on MILC $N_f=2+1$ lattices. Using methods developed recently for HPQCD’s study of $D\to K$, $l\nu$ decays, we find $f_{+}^{D\to \pi }(0)=0.666(29)$. This signifies a better than factor 2 improvement in errors for this quantity compared to previous calculations. Combining the new result with CLEO-c branching fraction data, we extract the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cd}|=0.225(6{)}_{\exp }(10{)}_{\mathrm{lat}}$, where the first error comes from experiment and the second from theory. With a total error of $\sim 5.3\%$ the accuracy of the direct determination of $|V_{cd}|$ from $D$ semileptonic decays has become comparable to (and in good agreement with) that from neutrino scattering. We also check for second row unitarity using this new $|V_{cd}|$, HPQCD’s earlier $|V_{cs}|$, and $|V_{cb}|$ from the Fermilab Lattice and MILC collaborations. We find $|V_{cd}{|}^2+|V_{cs}{|}^2+|V_{cb}{|}^2=0.976(50)$, improving on the current PDG2010 value.

In this note, we study the coupling of the technidilaton to the weak bosons. We consider two cases: (1) The dilaton directly couples to the weak bosons in a similar way as in the standard model. (2) The coupling in question is effectively induced only through the technifermion loops. In both cases, we find that the coupling is essentially determined by the mass-squared of the weak bosons over the dilaton decay constant.

We show that the discovery channel for dark matter (DM) production at colliders can be through flavor violating interactions resulting in a novel signature of a single top and large missing transverse energy. We discuss several examples where the production of DM is dominated by flavor violating couplings: minimal flavor violating models with a large bottom Yukawa, models with horizontal symmetries, and DM in nontrivial flavor group representations. Discovery at the 7 TeV LHC with a few ${\mathrm{fb}}^{-1}$ may already be possible.

We explore the role of a holographic Wilsonian cutoff in simple probe brane models with chiral symmetry breaking/restoration phase transitions. The Wilsonian cutoff allows us to define supergravity solutions for off-shell configurations and hence to define a potential for the chiral condensate. We pay particular attention to the need for configurations whose action we are comparing to have the same IR and UV boundary conditions. We exhibit new first- and second-order phase transitions with changing cutoff. We derive the effective potential for the condensate including mean-field and Berezinskii-Kosterlitz-Thouless type continuous transitions.

The nonzero strange quark mass effect in different types of single flavor color superconductivity and the phase diagram in a magnetic field are studied. We have obtained simple analytical forms of the quasiparticle energies for an arbitrary mass and explored the mass correction to the pressure and the transition temperature. It is found that the mass reduces the pressure and transition temperature of strange quarks, but it does not change the ranking $P_n<P_{\mathrm{A}}<P_{\mathrm{polar}}<P_{\mathrm{planar}}<P_{\mathrm{CSL}}$ of the pressure for the four canonical single flavor phases. The phase diagram with magnetic field and temperature for a system of three flavors is obtained for two different values of the strange quark mass. The changes from the one obtained previously under the approximation of massless strange quarks are examined.

Scattering is studied using a moduli space metric for well-separated vortices of non-Abelian vortices in $(2+1)$-dimensional $U(N)$ gauge theories with $N$ Higgs fields in the fundamental representation. Unlike vortices in the Abelian-Higgs model, the dynamics of non-Abelian vortices has many new features: the kinetic energy in real space can be transferred to that of internal orientational moduli and vice versa, the energy and charge transfer between two vortices, the scattering angle of collisions with a fixed impact parameter depends on the internal orientations, and some resonances appear due to synchronization of the orientations. Scattering of dyonic non-Abelian vortices in a mass deformed theory is also studied. We find a bound state of two vortices moving along coils around a circle, like a loop of a phone cord.

The decomposition of a one-loop scattering amplitude into elementary functions with rational coefficients introduces spurious singularities which afflict individual coefficients but cancel in the complete amplitude. These cancellations create a web of interactions between the various terms. We explore the extent to which entire one-loop amplitudes can be determined from these relationships starting with a relatively small input of initial information, typically the coefficients of the scalar integral functions as these are readily determined. In the context of one-loop gravity amplitudes, of which relatively little is known, we find that some amplitudes with a small number of legs can be completely determined from their box coefficients. For increasing numbers of legs, ambiguities appear which can be determined from the physical singularity structure of the amplitude. We illustrate this with the four-point and $\mathcal{N}=1,4$ five-point (super)gravity one-loop amplitudes.

We numerically obtain a class of soliton solutions for Einstein gravity in ($n+1$) dimensions coupled to massive Abelian gauge fields and with a negative cosmological constant with Lifshitz asymptotic behavior. We find that for all $n\ge 3$, a discrete set of magic values for the charge density at the origin (guaranteeing an asymptotically Lifshitz geometry) exists when the critical exponent associated with the Lifshitz scaling is $z=2$; moreover, in all cases, a single magic value is obtained for essentially every $1<z<2$, yet none when $z>2$ sufficiently.

We explore the cosmological solutions of a recently proposed extension of general relativity with a Lorentz-invariant mass term. We show that the same constraint that removes the Boulware-Deser ghost in this theory also prohibits the existence of homogeneous and isotropic cosmological solutions. Nevertheless, within domains of the size of inverse graviton mass we find approximately homogeneous and isotropic solutions that can well describe the past and present of the Universe. At energy densities above a certain crossover value, these solutions approximate the standard Friedmann-Robertson-Walker evolution with great accuracy. As the Universe evolves and density drops below the crossover value the inhomogeneities become more and more pronounced. In the low-density regime each domain of the size of the inverse graviton mass has essentially non-Friedmann-Robertson-Walker. cosmology. This scenario imposes an upper bound on the graviton mass, which we roughly estimate to be an order of magnitude below the present-day value of the Hubble parameter. The bound becomes especially restrictive if one utilizes an exact self-accelerated solution that this theory offers. Although the above are robust predictions of massive gravity with an explicit mass term, we point out that if the mass parameter emerges from some additional scalar field condensation, the constraint no longer forbids the homogeneous and isotropic cosmologies. In the latter case, there will exist an extra light scalar field at cosmological scales, which is screened by the Vainshtein mechanism at shorter distances.

We study the dynamical description of scalar-tensor gravity by performing the best-fit analysis for two cases of exponential and power-law form of the potential and scalar field function coupled to the curvature. The models are then tested against observational data. The results show that in both scenarios the Universe undergoes an acceleration expansion period and the geometrical equivalent of dark energy is associated with a time-dependent equation of state.

In a previous paper [K. Kleidis, D. B. Papadopoulos, E. Verdaguer, and L. Vlahos, Phys. Rev. D 78, 024027 (2008).] we considered the possibility that (within the early-radiation epoch) there has been (also) a short period of a significant presence of cosmic strings. During this radiation-plus-strings stage the Universe matter-energy content can be modeled by a two-component fluid, consisting of radiation (dominant) and a cosmic-string fluid (subdominant). It was found that, during this stage, the cosmological gravitational waves—that had been produced in an earlier (inflationary) epoch—with comoving wave numbers below a critical value (which depends on the physics of the cosmic-string network) were filtered, leading to a distorsion in the expected (scale-invariant) cosmological gravitational wave power spectrum. In any case, the cosmological evolution gradually results in the scaling of any long-cosmic-string network and, hence, after a short time interval, the Universe enters into the late-radiation era. However, along the transition from an early-radiation epoch to the late-radiation era through the radiation-plus-strings stage, the time dependence of the cosmological scale factor is modified, something that leads to a discontinuous change of the corresponding scalar curvature, which, in turn, triggers the quantum-mechanical creation of gravitons. In this paper we discuss several aspects of such a process, and, in particular, the observational consequences on the expected gravitational-wave power spectrum.