We present a systematic derivation of the constraints that the relativity principle imposes between coefficients of a deformed (but rotational invariant) momentum composition law, dispersion relation, and momentum transformation laws, at first order in a power expansion of an ultraviolet energy scale. This work generalizes previous results of universal relativistic kinematics to the case of particle-dependent relativistic kinematics, which can have interesting phenomenological applications that we explore in the second part of the manuscript.

We show that the nonzero electron mass plays a critical role in determining the magnetic properties of neutron stars by suppressing the generation of the chiral charge density needed to trigger a strong chiral plasma instability during the core collapse of supernovae. This instability has been proposed as a plausible mechanism for generating extremely large helical magnetic fields in neutron stars at their birth; the mechanism relies on the generation of a large nonequilibrium chiral charge density via electron capture reactions that selectively deplete left-handed electrons during core collapse and the early evolution of the protoneutron star. Our calculation shows that the electron chirality violation rate induced by Rutherford scattering, despite being suppressed by the smallness of the electron mass relative to the electron chemical potential, is still fast compared to the weak interaction electron capture rate. The resulting asymmetry between right- and left-handed electron densities is therefore unlikely to attain an astrophysically relevant magnitude.

We consider the Casimir interaction between two spheres corresponding to massless Dirac fields with MIT-bag boundary conditions. Using operator approach, we derive the TGTG formula for the Casimir interaction energy between the two spheres. A byproduct is the explicit formula for the translation matrix that relates the fermionic spherical waves in different coordinate systems. In the large separation limit, it is found that the order of the Casimir interaction energy is $L^{-5}$, where $L$ is the separation between the centers of the spheres. This order is intermediate between that of two Dirichlet spheres (of order $L^{-3}$) and two Neumann spheres (of order $L^{-7}$). In the small separation limit, we derive analytically the asymptotic expansion of the Casimir interaction energy up to the next-to-leading order term. The leading term agrees with the proximity force approximation. The result for the next-to-leading order term is compared to the corresponding results for scalar fields and electromagnetic fields.

The detection of a stochastic gravitational-wave signal from the superposition of many inspiraling supermassive black holes with pulsar timing arrays (PTAs) is likely to occur within the next decade. With this detection will come the opportunity to learn about the processes that drive black-hole-binary systems toward merger through their effects on the gravitational-wave spectrum. We use Bayesian methods to investigate the extent to which effects other than gravitational-wave emission can be distinguished using PTA observations. We show that, even in the absence of a detection, it is possible to place interesting constraints on these dynamical effects for conservative predictions of the population of tightly bound supermassive-black-hole binaries. For instance, if we assume a relatively weak signal consistent with a low number of bound binaries and a low black-hole-mass to galaxy-mass correlation, we still find that a nondetection by a simulated array, with a sensitivity that should be reached in practice within a few years, disfavors gravitational-wave-dominated evolution with an odds ratio of $\sim 30:1$. Such a finding would suggest either that all existing astrophysical models for the population of tightly bound binaries are overly optimistic, or else that some dynamical effect other than gravitational-wave emission is actually dominating binary evolution even at the relatively high frequencies/small orbital separations probed by PTAs.

In this paper, we present a new solution of the vacuum Einstein equations in five dimensions which is a static black hole with hyperscaling violation and with a three-dimensional horizon modeled by one of the eight Thurston geometries, namely the Nil geometry. This homogeneous geometry is nontrivial in the sense that it is neither of constant curvature nor a product of constant curvature manifolds. Using the Hamiltonian formalism, we identify the mass and entropy of the black hole solution. Curiously enough, in spite of the fact that the entropy turns out to be negative, the mass is positive and the first law of thermodynamics holds. We also discuss the extension in higher dimensions.

We study the post-Newtonian expansion of a class of Lorentz-violating gravity theories that reduce to khronometric theory (i.e. the infrared limit of Hořava gravity) in high-acceleration regimes and reproduce the phenomenology of modified Newtonian dynamics (MOND) in the low-acceleration, nonrelativistic limit. Like in khronometric theory, Lorentz symmetry is violated in these theories by introducing a dynamical scalar field (the “khronon”) whose gradient is enforced to be timelike. As a result, hypersurfaces of constant khronon define a preferred foliation of the spacetime, and the khronon can be thought of as a physical absolute time. The MOND phenomenology arises as a result of the presence, in the action, of terms depending on the acceleration of the congruence orthogonal to the preferred foliation. We find that if the theory is forced to reduce exactly to general relativity (rather than to khronometric theory) in the high-acceleration regime, the post-Newtonian expansion breaks down at low accelerations, and the theory becomes strongly coupled. Nevertheless, we identify a sizeable region of the parameter space where the post-Newtonian expansion remains perturbative for all accelerations, and the theory passes both Solar System and pulsar gravity tests, besides producing a MOND phenomenology for the rotation curves of galaxies. We illustrate this explicitly with a toy model of a system containing only baryonic matter but no dark matter.

We present the most general parametrization of models of dark energy in the form of a scalar field which is explicitly coupled to dark matter. We follow and extend the parametrized post-Friedmannian approach, previously applied to modified gravity theories, in order to include interacting dark energy. We demonstrate its use through a number of worked examples and show how the initially large parameter space of free functions can be significantly reduced and constrained to include only a few nonzero coefficients. This paves the way for a model-independent approach to classify and test interacting dark energy theories.

We present a new formalism designed to discover dark matter annihilation occurring in the Milky Way’s dwarf galaxies. The statistical framework extracts all available information in the data by simultaneously combining observations of all the dwarf galaxies and incorporating the impact of particle physics properties, the distribution of dark matter in the dwarfs, and the detector response. The method performs maximally powerful frequentist searches and produces confidence limits on particle physics parameters. Probability distributions of test statistics under various hypotheses are constructed exactly, without relying on large sample approximations. The derived limits have proper coverage by construction and claims of detection are not biased by imperfect background modeling. We implement this formalism using data from the Fermi Gamma-ray Space Telescope to search for an annihilation signal in the complete sample of Milky Way dwarfs whose dark matter distributions can be reliably determined. We find that the observed data are consistent with background for each of the dwarf galaxies individually as well as in a joint analysis. The strongest constraints are at small dark matter particle masses. Taking the median of the systematic uncertainty in dwarf density profiles, the cross section upper limits are below the pure $s$-wave weak scale relic abundance value ($2.2\times 10^{-26}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$) for dark matter masses below 26 GeV (for annihilation into $b\overline{b}$), 29 GeV (${\tau }^{+}{\tau }^{-}$), 35 GeV ($u\overline{u},d\overline{d},s\overline{s},c\overline{c}$, and $gg$), 6 GeV ($e^{+}{e}^{-}$), and 114 GeV ($\gamma \gamma$). For dark matter particle masses less than 1 TeV, these represent the strongest limits obtained to date using dwarf galaxies.

In this work we study superinflation in the context of the emergent universe (EU) scenario. The existence of a superinflating phase before the onset of slow-roll inflation arises in any emergent universe model. We found that the superinflationary period in the EU scenario produces a suppression of the CMB anisotropies at large scale which could be responsible for the observed lack of power at large angular scales of the CMB.

The integrated Sachs-Wolfe (ISW) effect measures the decay of the gravitational potential due to cosmic acceleration and is thus a direct probe of dark energy. In some of the earlier studies, the amplitude of the ISW effect was found to be in tension with the predictions of the standard Lambda cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) model. We measure the cross power of galaxies and active galactic nuclei (AGN) from the Wide-field Infrared Survey Explorer mission with cosmic microwave background temperature data from WMAP9 in order to provide an independent measurement of the ISW amplitude. Cross-correlations with the recently released Planck lensing potential maps are used to calibrate the bias and contamination fraction of the sources, thus avoiding systematic effects that could be present when using autospectra to measure bias. We find an amplitude of the cross power of $\mathcal{A}=1.24\pm 0.47$ from the galaxies and $\mathcal{A}=0.88\pm 0.74$ from the AGN, fully consistent with the $\mathrm{\Lambda }\mathrm{CDM}$ prediction of $\mathcal{A}=1$. The ISW measurement signal-to-noise ratio is 2.7 and 1.2 respectively. Comparing the amplitudes of the Galaxy and AGN cross-correlations, which arise from different redshifts, we find no evidence for redshift evolution in dark energy properties, consistent with a cosmological constant.

We consider indirect detection signals of atomic dark matter, with a massive dark photon which mixes kinetically with hypercharge. In significant regions of parameter space, dark matter remains at least partially ionized today, and dark atom formation can occur efficiently in dense regions, such as the centers of galactic halos. The formation of dark atoms is accompanied by emission of a dark photon, which can subsequently decay into Standard Model particles. We discuss the expected signal strength and compare it to that of annihilating dark matter. As a case study, we explore the possibility that dark atom formation can account for the observed 511 keV line and outline the relevant parameter space.

We perform unbiased tests for the clumpiness of the Universe by confronting the Zel’dovich-Kantowski-Dyer-Roeder luminosity distance, which describes the effect of local inhomogeneities on the propagation of light with the observational one estimated from measurements of standard candles, i.e., type Ia supernovae (SNe Ia) and gamma-ray bursts (GRBs). Methodologically, we first determine the light-curve fitting parameters which account for distance estimation in SNe Ia observations and the luminosity/energy relations which are responsible for distance estimation of GRBs in the global fit to reconstruct the Hubble diagrams in the context of a clumpy Universe. Subsequently, these Hubble diagrams allow us to achieve unbiased constraints on the matter density parameter ${\mathrm{\Omega }}_m$, as well as the clumpiness parameter $\eta$ which quantifies the fraction of homogeneously distributed matter within a given light cone. At a $1\sigma$ confidence level, the constraints are ${\mathrm{\Omega }}_m=0.34\pm 0.02$ and $\eta =1.00_{-0.02}^{+0.00}$ from the joint analysis. The results suggest that the Universe full of Friedman-Lemaître-Robertson-Walker fluid is favored by observations of standard candles with very high statistical significance. On the other hand, they may also indicate that the Zel’dovich-Kantowski-Dyer-Roeder approximation is a sufficiently accurate form to describe the effects of local homogeneity on the expanding Universe.

We show that the cosmic ray (CR) knee can be entirely explained by energy-dependent CR leakage from the Milky Way, with an excellent fit to all existing data. We test this hypothesis calculating the trajectories of individual CRs in the Galactic magnetic field. We find that the CR escape time ${\tau }_{\text{esc}}(E)$ exhibits a knee-like structure around $E/Z=\text{few}\times {10}^{15}\mathrm{eV}$ for small coherence lengths and strengths of the turbulent magnetic field. The resulting intensities for different groups of nuclei are consistent with the ones determined by KASCADE and KASCADE-Grande, using simple power laws as injection spectra. The transition from Galactic to extragalactic CRs is terminated at $\approx 2\times {10}^{18}\mathrm{eV}$, while extragalactic CRs contribute significantly to the subdominant proton flux already for $\gtrsim 2\times {10}^{16}\mathrm{eV}$. The natural source of extragalactic CRs in the intermediate energy region up to the ankle are in this model normal and starburst galaxies. The escape model provides a good fit to $\ln (A)$ data; it predicts that the phase of the CR dipole varies strongly in the energy range between $1\times {10}^{17}$ and $3\times {10}^{18}\mathrm{eV}$, while our estimate for the dipole magnitude is consistent with observations.

We explore the possibilities in two-Higgs-doublet models of type I and type II for Higgs states with mass below about 60 GeV, i.e. less than half of the $\sim 125\mathrm{GeV}$ mass of the observed SM-like Higgs boson. We identify the latter as either the lighter or the heavier $CP$-even state, $h$ or $H$, and employ scans of the two-Higgs-doublet model parameter space taking into account all relevant theoretical and experimental constraints, including the most up-to-date Higgs signal strength measurements. We find that, in both type I and type II models, such light Higgs states are phenomenologically viable and can lead to interesting signatures. Part of the relevant parameter space may be testable with the existing 8 TeV LHC data, e.g. by looking for direct production of the light state via $gg$ fusion or $b\overline{b}$ associated production using its ${\tau }^{+}{\tau }^{-}$ and ${\mu }^{+}{\mu }^{-}$ decays at low invariant mass.

Models in which dark matter particles can scatter into a slightly heavier state which promptly decays to the lighter state and a photon (known as eXciting Dark Matter, or XDM) have been shown to be capable of generating the 3.55 keV line observed from galaxy clusters, while suppressing the flux of such a line from smaller halos, including dwarf galaxies. In most of the XDM models discussed in the literature, this up-scattering is mediated by a new light particle, and dark matter annihilations proceed into pairs of this same light state. In these models, the dark matter and the mediator effectively reside within a hidden sector, without sizable couplings to the Standard Model. In this paper, we explore a model of XDM that does not include a hidden sector. Instead, the dark matter both up-scatters and annihilates through the near resonant exchange of an $\mathcal{O}(10^2)\mathrm{GeV}$ pseudoscalar with large Yukawa couplings to the dark matter and smaller, but non-neglibile, couplings to Standard Model fermions. The dark matter and the mediator are each mixtures of Standard Model singlets and $SU(2{)}_W$ doublets. We identify parameter space in which this model can simultaneously generate the 3.55 keV line and the gamma-ray excess observed from the Galactic center, without conflicting with constraints from colliders, direct detection experiments, or observations of dwarf galaxies.

Motivated by the recent LHCb measurements on ${\overline{B}}_s\to {\pi }^{-}{K}^{*+}$ and ${\overline{B}}_s\to K^{\pm }{K}^{*\mp }$ decay modes, we revisit the $B_s\to PV$ decays within QCD factorization framework. The effects of hard-spectator scattering and annihilation corrections are studied in detail. After performing a ${\chi }^2$-fit on the end-point parameters $X_A^{i,f}({\rho }_A^{i,f},{\varphi }_A^{i,f})$ and $X_H({\rho }_H,{\varphi }_H)$ with available data, it is found that although some possible mismatches exist, the universalities of $X_A^{i,f}$ and $X_H$ in $B_s$ and $B_{u,d}$ systems are still allowed within theoretical uncertainties and experimental errors. With the end-point parameters obtained from $B_{u,d}\to PV$ decays, the numerical results and detailed analyses for the observables of ${\overline{B}}_s\to \pi K^{*}$, $\rho K$, $\pi \rho$, $\pi \varphi$, and $K\varphi$ decay modes are presented. In addition, we have identified a few useful observables, especially the ones of ${\overline{B}}_s\to {\pi }^0\varphi$ decay for instance, for probing hard-spectator scattering and annihilation contributions.

We find using the minimal left-right symmetric model that the presence of leptonic $CP$ violation can radiatively generate a strong $CP$ phase at the one-loop level itself, which can be beyond the current bounds established by the neutron electric dipole moment experiments. If there are no axions or unnatural cancellations, this leads to the testable prediction that leptonic $CP$ violation must be negligibly small (Dirac phase ${\delta }_{CP}=0$ or $\pi$), in wide and interesting regions of parameter space.

In the context of the AdS/CFT correspondence, we study several holographic probes that relate information about the bulk spacetime to CFT data. The best-known example is the relation between minimal surfaces in the bulk and entanglement entropy of a subregion in the CFT. Building on earlier work, we identify “shadows” in the bulk: regions that are not illuminated by any of the bulk probes we consider, in the sense that the bulk surfaces do not pass through these regions. We quantify the size of the shadow in the near-horizon region of a black hole and in the vicinity of a sufficiently dense star. The existence of shadows motivates further study of the bulk-boundary dictionary in order to identify CFT quantities that encode information about the shadow regions in the bulk. We speculate on the interpretation of our results from a dual field theory perspective.

We extend the investigation of BPS saturated ’t Hooft-Polyakov monopoles in ${\mathcal{M}}^2\times S^2$ to the general case of $SU(N)$ gauge symmetry. This geometry causes the resulting $N-1$ coupled nonlinear ordinary differential equations for the $N-1$ monopole profiles to become autonomous. One can also define a flat limit in which the curvature of the background metric is arbitrarily small but the simplifications brought in by the geometry remain. We prove analytically that nontrivial solutions in which the profiles are not proportional can be found. Moreover, we construct numerical solutions for $N=2,3$ and 4. The presence of the parameter $N$ allows one to take a smooth large $N$ limit which greatly simplifies the treatment of the infinite number of profile function equations. We show that, in this limit, the system of infinitely many coupled ordinary differential equations for the monopole profiles reduces to a single two-dimensional nonlinear partial differential equation.

Using the worldline $SU(2|1)$ superfield approach, we construct $\mathcal{N}=4$ superconformally invariant actions for the $d=1$ multiplets ($\mathbf{1},\mathbf{4},\mathbf{3}$) and ($\mathbf{2},\mathbf{4},\mathbf{2}$). The $SU(2|1)$ superfield framework automatically implies the trigonometric realization of the superconformal symmetry and the harmonic oscillator term in the corresponding component actions. We deal with the general $\mathcal{N}=4$ superconformal algebra $D(2,1;\alpha )$ and its central-extended $\alpha =0$ and $\alpha =-1$ $psu(1,1|2)\oplus su(2)$ descendants. We capitalize on the observation that $D(2,1;\alpha )$ at $\alpha \ne 0$ can be treated as a closure of its two $su(2|1)$ subalgebras, one of which defines the superisometry of the $SU(2|1)$ superspace, while the other is related to the first one through the reflection of $\mu$, the parameter of contraction to the flat $\mathcal{N}=4,d=1$ superspace. This closure property and its $\alpha =0$ analog suggest a simple criterion for the $SU(2|1)$ invariant actions to be superconformal: they should be even functions of $\mu$. We find that the superconformal actions of the multiplet ($\mathbf{2},\mathbf{4},\mathbf{2}$) exist only at $\alpha =-1,0$ and are reduced to a sum of the free sigma-model-type action and the conformal superpotential yielding, respectively, the oscillator potential $\sim {\mu }^2$ and the standard conformal inverse-square potential in the bosonic sector. The sigma-model action in this case can be constructed only on account of nonzero central charge in the superalgebra $su(1,1|2)$.