Light scalar fields with only gravitational strength couplings are typically present in UV complete theories of physics beyond the standard model. In the early universe it is natural for these fields to dominate the energy density, and their subsequent decay—if prior to big bang nucleosynthesis—will typically yield some dark matter particles in their decay products. In this paper we make the observation that a Nonthermal “WIMP Miracle” may result: that is, in the simplest solution to the cosmological moduli problem, nonthermally produced WIMPs can naturally account for the observed dark matter relic density.

Future or ongoing galaxy redshift surveys can put stringent constraints on neutrinos masses via the high-precision measurements of galaxy power spectrum, when combined with CMB information. In this paper we develop a method to model galaxy power spectrum in the weakly nonlinear regime for a mixed dark matter [cold dark matter (CDM) plus finite-mass neutrinos] model, based on perturbation theory (PT) whose validity is well tested by simulations for a CDM model. In doing this we carefully study various aspects of the nonlinear clustering (nonlinear neutrino perturbations and the higher-order growth functions), and then arrive at a useful approximation allowing for a quick computation of the nonlinear power spectrum as in the CDM case. The nonlinear galaxy bias is also included in a self-consistent manner within the PT framework. Thus, the use of our PT model can give a more robust understanding of the measured galaxy power spectrum as well as allow for higher sensitivity to neutrino masses due to the gain of Fourier modes beyond the linear regime. Based on the Fisher matrix formalism, we find that the BOSS or Stage-III type survey, when combined with Planck CMB information, gives a precision of total neutrino mass constraint, $\sigma (m_{\nu ,\mathrm{tot}})\simeq 0.1\mathrm{eV}$, while the Stage-IV type survey may achieve $\sigma (m_{\nu ,\mathrm{tot}})\simeq 0.05\mathrm{eV}$, i.e., more than a $1\mathrm{\text{−}}\sigma$ detection of neutrino masses. We also discuss possible systematic errors on dark energy parameters caused by the neutrino mass uncertainty. The significant correlation between neutrino mass and dark energy parameters is found, if the information on power spectrum amplitude is included. More importantly, for the Stage-IV type survey, a best-fit dark energy model may be biased and falsely away from the underlying true model by more than the $1\mathrm{\text{−}}\sigma$ statistical errors, if neutrino mass is ignored in the model fitting.

We apply a recently developed analytic model for the evolution of monopole networks to the case of monopoles attached to one string, usually known as hybrid networks. We discuss scaling solutions for both local and global hybrid networks, and also find an interesting application for the case of vortons. Our quantitative results agree with previous estimates in indicating that the hybrid networks will usually annihilate soon after the string-forming phase transition. However, we also show that in some specific circumstances these networks can survive considerably more than a Hubble time.

The perfect fluid in the context of a covariant variable speed of light theory proposed by J. Magueijo is studied. On the one hand the modified first law of thermodynamics together with a recipe to obtain equations of state are obtained. On the other hand the Newtonian limit is performed to obtain the nonrelativistic hydrostatic equilibrium equation for the theory. The results obtained are used to determine the time variation of the radius of Mercury induced by the variability of the speed of light ($c$), and the scalar contribution to the luminosity of white dwarfs. Using a bound for the change of that radius and combining it with an upper limit for the variation of the fine structure constant, a bound on the time variation of $c$ is set. An independent bound is obtained from luminosity estimates for Stein 2015B.

We discuss how, in the presence of higher-dimensional operators, the standard model fermion masses can be misaligned in flavor space with the Yukawa couplings to the Higgs boson, even with only one Higgs doublet. Such misalignment results in flavor-violating couplings to the Higgs and hence flavor-changing neutral current processes from tree-level Higgs exchange. We perform a model-independent analysis of such an effect. Specializing to the framework of a composite Higgs with partially composite standard model gauge and fermion fields, we show that the constraints on the compositeness scale implied by ${ϵ}_K$ can be generically as strong as those from the exchange of heavy spin-1 resonances if the Higgs is light and strongly coupled to the new states. In the special and well-motivated case of a composite pseudo-Goldstone Higgs, we find that the shift symmetry acting on the Higgs forces an alignment of the fermion mass terms with their Yukawa couplings at leading order in the fermions’ degree of compositeness, thus implying much milder bounds. As a consequence of the flavor-violating Higgs couplings, we estimate $\mathrm{BR}(t\to ch)\sim {10}^{-4}$ and $\mathrm{BR}(h\to tc)\sim 5\times {10}^{-3}$ both for a pseudo-Goldstone (if $t_R$ is fully composite) and for a generic composite Higgs. By virtue of the AdS/CFT correspondence, our results directly apply to 5-dimensional Randall-Sundrum compactifications.

The masses of the lowest-lying states in the meson and in the gluonic sector of an SU(2) gauge theory with two Dirac flavors in the adjoint representation are measured on the lattice at a fixed value of the lattice coupling $\beta =4/g_0^2=2.25$ for values of the bare fermion mass $m_0$ that span a range between the quenched regime and the massless limit, and for various lattice volumes. Even for light constituent fermions the lightest glueballs are found to be lighter than the lightest mesons. Moreover, the string tension between two static fundamental sources strongly depends on the mass of the dynamical fermions and becomes of the order of the inverse squared lattice linear size before the chiral limit is reached. The implications of these findings for the phase of the theory in the massless limit are discussed and a strategy for discriminating between the (near-)conformal and the confining scenario is outlined.

Only two isospin-singlet scalar mesons $f_0(600)$ ($\sigma$) and $f_0(980)$ exist below 1 GeV, so that it is natural to suppose that they are two energy eigenstates which are mixtures of $\frac{1}{\sqrt{2}}(u\overline{u}+d\overline{d})$ and $s\overline{s}$. Is this picture right? Generally, it is considered that $f_0(600)$ mainly consists of $\frac{1}{\sqrt{2}}(u\overline{u}+d\overline{d})$; if so, the dominant component of $f_0(980)$ should be $s\overline{s}$. The recent measurement of the CLEO Collaboration on the branching ratio of $D_s\to f_0(980)e^{+}{\nu }_e$ provides an excellent opportunity to test the structure of $f_0(980)$, namely, whether the data can be understood as long as it consists of mainly the conventional $q\overline{q}$ structure. We calculate the form factors of $D_s\to f_0(980)$ in the light-front quark model and the corresponding branching ratio of the semileptonic decay. By fitting the data, we obtain the mixing angle $\varphi$. The obtained mixing angle shows that the $s\overline{s}$ component in $f_0(980)$ may not be dominant.

We studied a left-right symmetric model that can accommodate the neutrino dark energy ($\nu \mathrm{DE}$) proposal. The type-III seesaw mechanism is implemented to give masses to the neutrinos. After explaining the model, we study the consistency of the model by minimizing the scalar potential and obtaining the conditions for the required vacuum expectation values of the different scalar fields. This model is then embedded in an $SO(10)$ grand unified theory and the allowed symmetry breaking scales are determined by the condition of the gauge coupling unification. Although $SU(2{)}_{\mathrm{R}}$ breaking is required to be high, its Abelian subgroup $U(1{)}_{\mathrm{R}}$ is broken in the TeV range, which can then give the required neutrino masses and predicts new gauge bosons that could be detected at LHC. The neutrino masses are studied in detail in this model, which shows that at least 3 singlet fermions are required.

We demonstrate that recent measurements of cosmic microwave background temperature and polarization anisotropy made by the ACBAR, QUAD, and BICEP experiments substantially improve the cosmological constraints on possible variations of the fine structure constant in the early universe. This data, combined with the five year observations from the WMAP mission, yield the constraint $\alpha /{\alpha }_0=0.987\pm 0.012$ at 68% C.L. The inclusion of the new Hubble Space Telescope constraints on the Hubble constant further increases the accuracy to $\alpha /{\alpha }_0=1.001\pm 0.007$ at 68% C.L., bringing possible deviations from the current value below the 1% level and improving previous constraints by a factor of $\sim 3$.

We study correlation functions of single-cycle chiral operators in ${\mathrm{Sym}}^N{T}^4$, the symmetric product orbifold of $N$ supersymmetric four-tori. Correlators of twist operators are evaluated on covering surfaces, generally of different genera, where fields are single valued. We compute some simple four-point functions and study how the sum over inequivalent branched covering maps splits under operator product expansions. We then discuss extremal $n$-point correlators, i.e. correlators of $n-1$ chiral and one antichiral operators. They obey simple recursion relations involving numbers obtained from counting branched covering maps with particular properties. In most cases we are able to solve explicitly the recursion relations. Remarkably, extremal correlators turn out to be equal to Hurwitz numbers.

We reveal nonmanifest gauge and $SO(1,5)$ Lorentz symmetries in the Lagrangian description of a six-dimensional free chiral field derived from the Bagger-Lambert-Gustavsson model in [P.-M. Ho and Y. Matsuo, J. High Energy Phys. 06 (2008) 105.] and make this formulation covariant with the use of a triplet of auxiliary scalar fields. We consider the coupling of this self-dual construction to gravity and its supersymmetrization. In the case of the nonlinear model of [P.-M. Ho, Y. Imamura, Y. Matsuo, and S. Shiba, J. High Energy Phys. 08 (2008) 014.] we solve the equations of motion of the gauge field, prove that its nonlinear field strength is self-dual and find a gauge-covariant form of the nonlinear action. Issues of the relation of this model to the known formulations of the M5-brane worldvolume theory are discussed.

The group structure of the variant chiral symmetry discovered by Lüscher in the Ginsparg-Wilson description of lattice chiral fermions is analyzed. It is shown that the group contains an infinite number of linearly independent symmetry generators, and the Lie algebra is given explicitly. $CP$ is an automorphism of this extended chiral group, and the $CP$ transformation properties of the symmetry generators are found. The group has an infinite-parameter invariant subgroup, and the factor group, whose elements are its cosets, is isomorphic to the continuum chiral symmetry group. Features of the currents associated with these symmetries are discussed, including the fact that some different, noncommuting symmetry generators lead to the same Noether current. These are universal features of lattice chiral fermions based on the Ginsparg-Wilson relation; they occur in the overlap, domain-wall, and perfect-action formulations. In a solvable example, free overlap fermions, these noncanonical elements of lattice chiral symmetry are related to complex energy singularities that violate reflection positivity and impede continuation to Minkowski space.

We study the various linear responses of neutron stars to external relativistic tidal fields. We focus on three different tidal responses, associated to three different tidal coefficients: (i) a gravito-electric-type coefficient $G{\mu }_{\ell }=[\mathrm{\text{length}}{]}^{2\ell +1}$ measuring the $\ell$th-order mass multipolar moment $G{M}_{a_1\dots a_{\ell }}$ induced in a star by an external $\ell$th-order gravito-electric tidal field $G_{a_1\dots a_{\ell }}$; (ii) a gravito-magnetic-type coefficient $G{\sigma }_{\ell }=[\mathrm{\text{length}}{]}^{2\ell +1}$ measuring the $\ell$th spin multipole moment $G{S}_{a_1\dots a_{\ell }}$ induced in a star by an external $\ell$th-order gravito-magnetic tidal field $H_{a_1\dots a_{\ell }}$; and (iii) a dimensionless “shape” Love number $h_{\ell }$ measuring the distortion of the shape of the surface of a star by an external $\ell$th-order gravito-electric tidal field. All the dimensionless tidal coefficients $G{\mu }_{\ell }/R^{2\ell +1}$, $G{\sigma }_{\ell }/R^{2\ell +1}$, and $h_{\ell }$ (where $R$ is the radius of the star) are found to have a strong sensitivity to the value of the star’s “compactness” $c\equiv GM/(c_0^{2}R)$ (where we indicate by $c_0$ the speed of light). In particular, $G{\mu }_{\ell }/R^{2\ell +1}\sim k_{\ell }$ is found to strongly decrease, as $c$ increases, down to a zero value as $c$ is formally extended to the “black hole (BH) limit” $c^{\mathrm{BH}}=1/2$. The shape Love number $h_{\ell }$ is also found to significantly decrease as $c$ increases, though it does not vanish in the formal limit $c\to c^{\mathrm{BH}}$, but is rather found to agree with the recently determined shape Love numbers of black holes. The formal vanishing of ${\mu }_{\ell }$ and ${\sigma }_{\ell }$ as $c\to c^{\mathrm{BH}}$ is a consequence of the no-hair properties of black holes. This vanishing suggests, but in no way proves, that the effective action describing the gravitational interactions of black holes may not need to be augmented by nonminimal worldline couplings.

We complete the analysis carried out in previous papers by studying the Hawking radiation for a Kerr black hole carried to infinity by fermionic currents of any spin. We find agreement with the thermal spectrum of the Hawking radiation for fermionic degrees of freedom. We start by showing that the near-horizon physics for a Kerr black hole is approximated by an effective two-dimensional field theory of fermionic fields. Then, starting from two-dimensional currents of any spin that form a $W_{1+\infty }$ algebra, we construct an infinite set of covariant currents, each of which carries the corresponding moment of the Hawking radiation. All together they agree with the thermal spectrum of the latter. We show that the predictive power of this method is based not on the anomalies of the higher-spin currents (which are trivial) but on the underlying $W_{1+\infty }$ structure. Our results point toward the existence in the near-horizon geometry of a symmetry larger than the Virasoro algebra, which very likely takes the form of a $W_{\infty }$ algebra.

In the model of the de Sitter gauge theory of gravity, the empty homogenous and isotropic spacetimes with constant curvature scalar and nonvanishing homogenous and isotropic torsion must have de Sitter metrics. The static de Sitter spacetime with static, $O(3)$-symmetric, vector torsion is the only spherically symmetric, vacuum solution with the metric of the form $g_{\mu \nu }=\mathrm{diag}(A^2(r),-B^2(r),-r^2,-r^2{sin}^2\theta )$. The expressions of the torsion for different de Sitter spacetimes are presented. They are different from one to another. The properties of different de Sitter spacetimes with torsion are also studied.

We investigate the effect that the average backreaction of structure formation has on the dynamics of the cosmological expansion, within the concordance model. Our approach in the Poisson gauge is fully consistent up to second order in a perturbative expansion about a flat Friedmann background, including a cosmological constant. We discuss the key length scales which are inherent in any averaging procedure of this kind. We identify an intrinsic homogeneity scale that arises from the averaging procedure, beyond which a residual offset remains in the expansion rate and deceleration parameter. In the case of the deceleration parameter, this can lead to a quite large increase in the value, and may therefore have important ramifications for dark energy measurements, even if the underlying nature of dark energy is a cosmological constant. We give the intrinsic variance that affects the value of the effective Hubble rate and deceleration parameter. These considerations serve to add extra intrinsic errors to our determination of the cosmological parameters, and, in particular, may render attempts to measure the Hubble constant to percent precision overly optimistic.

It is well understood that spatial noncommutativity, if indeed realized in nature, is a phenomenon whose effects are not just felt at energy scales comparable to the noncommutativity scale. Loop effects can transmit signatures of any underlying noncommutativity to macroscopic scales (a manifestation of a phenomenon that has come to be known as UV/IR mode mixing) and offer a potential lever to constrain the amount of noncommutativity present in nature, if present at all. Field theories defined on noncommutative spaces (realized in string theory when $D$-branes are coupled to backgrounds of nontrivial RR background flux), can exhibit strong UV/IR mode mixing, manifesting in a nonlocal one-loop effective action. In the context of inflation in the presence of any background noncommutativity, we demonstrate how this UV/IR mixing at the loop level can allow us to place severe constraints on the scale of noncommutativity if we presume inflation is responsible for large-scale structure. We demonstrate that any amount of noncommutativity greatly suppresses the cosmic microwave background power at all observable scales, independent of the scale of inflation, and independent of whether or not the noncommutativity tensor redshifts during inflation, therefore nullifying a very salient and successful prediction of inflation.

It has recently been argued that the PAMELA, ATIC, and PPB-BETS data showing an anomalous excess of high-energy cosmic ray positrons and electrons might be explained by dark matter annihilating in the Galactic halo with a cross section resonantly enhanced compared to its value in the primeval plasma. We find that with a very large annihilation cross section the flash of energetic photons and electron-positron pairs expected from dark-matter annihilation in the first protohalos that form at redshift $z\sim 40$ is likely substantial and observable. As a consequence, bounds on the allowed energy injection into the primordial gas and the energy density of the diffuse gamma-ray background give rise to limits on the low-velocity dark-matter cross section that can be difficult to reconcile with this interpretation of the PAMELA, ATIC, and PPB-BETS results.

We investigate the consequences of replacing the global flavor symmetry of minimal flavor violation (MFV) $SU(3{)}_Q\times SU(3{)}_U\times SU(3{)}_D\times \cdots$ by a discrete ${\mathcal{D}}_Q\times {\mathcal{D}}_U\times {\mathcal{D}}_D\times \cdots$ symmetry. Goldstone bosons resulting from the breaking of the flavor symmetry generically lead to bounds on new flavor structure many orders of magnitude above the TeV scale. The absence of Goldstone bosons for discrete symmetries constitute the primary motivation of our work. Less symmetry implies further invariants and renders the mass-flavor basis transformation observable in principle and calls for a hierarchy in the Yukawa matrix expansion. We show, through the dimension of the representations, that the (discrete) symmetry in principle does allow for additional $\Delta F=2$ operators. If though the $\Delta F=2$ transitions are generated by two subsequent $\Delta F=1$ processes, as, for example, in the standard model, then the four crystal-like groups $\Sigma (168)\approx \mathrm{PSL}(2,{\mathbb{F}}_7)$, $\Sigma (72\phi )$, $\Sigma (216\phi )$ and especially $\Sigma (360\phi )$ do provide enough protection for a TeV-scale discrete MFV scenario. Models where this is not the case have to be investigated case by case. Interestingly $\Sigma (216\phi )$ has a (nonfaithful) representation corresponding to an $A_4$ symmetry. Moreover we argue that the, apparently often omitted, ($D$) groups are subgroups of an appropriate $\Delta (6g^2)$. We would like to stress that we do not provide an actual model that realizes the MFV scenario nor any other theory of flavor.

We determine the quark condensate and the dressed Polyakov loop from the finite temperature Landau gauge quark propagator evaluated with $U(1)$-valued boundary conditions in an approximation to quenched QCD. These gauge invariant quantities allow for an investigation of the chiral and deconfinement transitions. We compare results from Dyson-Schwinger equations on a lattice with infinite volume continuum results and study the temperature and quark mass dependence of both quantities. In particular we investigate the chiral condensate and the dressed Polyakov loop in the chiral limit. We also consider an alternative order parameter for the deconfinement transition, the dual scalar quark dressing, and compare it with the dressed Polyakov loop. As a result we find only slightly different transition temperatures for the chiral and the deconfinement transitions at finite quark masses; in the chiral limit both transitions coincide.