We present a description of cosmic neutrinos as a dispersive fluid. In this approach, the neutrino phase space is reduced to density and velocity fields alongside a scale-dependent sound speed. This sound speed depends on redshift, the initial neutrino phase space density and the cold dark matter gravitational potential. The latter is a new coupling between neutrinos and large scale structure not described by previous fluid approaches. We compute the sound speed in linear theory and find that it asymptotes to constants at small and large scales regardless of the gravitational potential. By comparing with neutrino N-body simulations, we measure the small scale sound speed and find it to be lower than linear theory predictions. This allows for an explanation of the discrepancy between N-body and linear response predictions for the neutrino power spectrum: neutrinos are still driven predominantly by the cold dark matter, but the sound speed on small scales is not stable to perturbations and decreases. Finally, we present a calibrated model for the neutrino power spectrum that requires no additional integrations outside of standard Boltzmann codes.

We compute the spectral index of primordial perturbations in a rainbow universe. We allow the Newton constant $G$ to run at (super-) Planckian energies and we consider both vacuum and thermal perturbations. If the rainbow metric is the one associated to a generalized Horava-Lifshitz dispersion relation, we find that only when $G$ tends asymptotically to 0 can one match the observed value of the spectral index and solve the horizon problem, both for vacuum and thermal perturbations. For vacuum fluctuations the observational constraints imply that the primordial universe expansion can be both accelerating or decelerating, while in the case of thermal perturbations only decelerating expansion is allowed.

A non-Abelian $SU(2)$ gauge field with a nonminimal Horndeski coupling to gravity gives rise to a de Sitter solution followed by a graceful exit to a radiation-dominated epoch. In this Horndeski-Yang-Mills (HYM) theory we derive the second-order action for tensor perturbations on the homogeneous and isotropic quasi–de Sitter background. We find that the presence of the Horndeski nonminimal coupling to the gauge field inevitably introduces ghost instabilities in the tensor sector during inflation. Moreover, we also find Laplacian instabilities for the tensor perturbations deep inside the Hubble radius during inflation. Thus, we conclude that the HYM theory does not provide a consistent inflationary framework due to the presence of ghosts and Laplacian instabilities.

Light propagation in two Swiss-cheese models based on anisotropic Szekeres structures is studied and compared with light propagation in Swiss-cheese models based on the Szekeres models’ underlying Lemaitre-Tolman-Bondi models. The study shows that the anisotropy of the Szekeres models has only a small effect on quantities such as redshift-distance relations, projected shear and expansion rate along individual light rays. The average angular diameter distance to the last scattering surface is computed for each model. Contrary to earlier studies, the results obtained here are (mostly) in agreement with perturbative results. In particular, a small negative shift, $\delta D_A≔\frac{D_A-D_{A,bg}}{D_{A,bg}}$, in the angular diameter distance is obtained upon line-of-sight averaging in three of the four models. The results are, however, not statistically significant. In the fourth model, there is a small positive shift which has an especially small statistical significance. The line-of-sight averaged inverse magnification at $z=1100$ is consistent with 1 to a high level of confidence for all models, indicating that the area of the surface corresponding to $z=1100$ is close to that of the background.

In this work, we simulate a set of realizations of the local volume dark matter subhalo population based on the distributions and relations derived from Via Lactea II $N$-body simulation. We calculate the J-factors of these subhalos, and find that the low mass subhalos contribute a lot to the total J-factors. Combining with 91 months of the Fermi LAT observation, we constrain on the cross section of dark matter annihilating directly to two gamma rays. This is the first work combining numerical simulation results and Fermi LAT observations to constrain the dark matter cross section to the gamma-ray line with the subhalo population. Though the constraints derived from the subhalo population are weaker than those from the Fermi LAT observation of the Galactic center, they are supportive of and complementary to these other results.

We show that the spectral split of a neutrino ensemble, which initially consists of electron type neutrinos, is analogous to the Bardeen-Cooper-Schrieffer–Bose-Einstein condensate (BCS-BEC) crossover already observed in ultracold atomic gas experiments. Such a neutrino ensemble mimics the deleptonization burst of a core collapse supernova. Although these two phenomena belong to very different domains of physics, the propagation of neutrinos from highly interacting inner regions of the supernova to the vacuum is reminiscent of the evolution of Cooper pairs between weak and strong interaction regimes during the crossover. The Hamiltonians and the corresponding many-body states undergo very similar transformations if one replaces the pair quasispin of the latter with the neutrino isospin of the former.

We show that in the scenario where dark matter (DM) particles annihilate through light mediators, the energy spectra of the final state cosmic-ray particles depend strongly on the mediator mass. For final state antiprotons, a spectrum with relatively narrow peak occurs when the mediator mass is comparable to the $\overline{p}p$ production threshold. Of interest, the latest AMS-02 data on the $\overline{p}/p$ flux ratio hint at a bumplike excess over the expected background in the energy range $\sim 100–450\mathrm{GeV}$. We show that such a light mediator scenario is favored by the latest AMS-02 data over the scenarios of DM direct annihilation into the standard model particles and that of antiprotons produced from inside supernova remnants (SNRs), and is consistent with the upper limits derived from the Fermi-LAT data on the gamma rays towards the dwarf spheroidal galaxies. The $\overline{p}/p$ flux ratio with energy above 450 GeV is predicted to fall with energy quickly, which can be easily distinguished from the other two scenarios as they predict the ratio to be flattening or rising up to the multi-TeV region.

We demonstrate that theoretical predictions using current resummation techniques for the lepton pair production (LPP) rapidity and $x_F$ distributions can be inconsistent with data in high rapidity and $x_F$ kinematic regions by observing their effect in global fits of parton distribution functions (PDFs). We present an enhanced resummation technique for the LPP rapidity and $x_F$ distributions that agrees with LPP data. The enhanced resummation method is used in conjunction with threshold resummation in deep inelastic scattering to perform two global fits of PDFs using the minimal and Borel prescriptions. The results are analyzed to determine the effect of threshold resummation on global fits of PDFs.

Many theories of dark matter (DM) predict that DM particles can be captured by stars via scattering on ordinary matter. They subsequently condense into a DM core close to the center of the star and eventually annihilate. In this work, we trace DM capture and annihilation rates throughout the life of a massive star and show that this evolution culminates in an intense annihilation burst coincident with the death of the star in a core collapse supernova. The reason is that, along with the stellar interior, also its DM core heats up and contracts, so that the DM density increases rapidly during the final stages of stellar evolution. We argue that, counterintuitively, the annihilation burst is more intense if DM annihilation is a $p$-wave process than for $s$-wave annihilation because in the former case, more DM particles survive until the supernova. If among the DM annihilation products are particles like dark photons that can escape the exploding star and decay to standard model particles later, the annihilation burst results in a flash of gamma rays accompanying the supernova. For a galactic supernova, this “dark gamma-ray burst” may be observable in the Čerenkov Telescope Array.

Inflection-point inflation is an interesting possibility to realize a successful slow-roll inflation when inflation is driven by a single scalar field, with its value during inflation below the Planck mass (${\varphi }_I\lesssim M_{\mathrm{Pl}}$). In order for a renormalization group (RG) improved effective $\lambda {\varphi }^4$ potential to develop an inflection point, the running quartic coupling $\lambda (\varphi )$ must exhibit a minimum with an almost vanishing value in its RG evolution, namely $\lambda ({\varphi }_I)\simeq 0$ and ${\beta }_{\lambda }({\varphi }_I)\simeq 0$, where ${\beta }_{\lambda }$ is the beta function of the quartic coupling. In this paper, we consider the inflection-point inflation in the context of the minimal ${\mathrm{U}(1)}_X$ extended Standard Model (SM), a generalization of the minimal $\mathrm{U}(1{)}_{B-L}$ model, where the ${\mathrm{U}(1)}_X$ symmetry is realized as a linear combination of the SM ${\mathrm{U}(1)}_Y$ and the $\mathrm{U}(1{)}_{B-L}$ gauge symmetries. We identify the ${\mathrm{U}(1)}_X$ Higgs field with the inflaton field. For successful inflection-point inflation to be consistent with the current cosmological observations, the mass ratios among the ${\mathrm{U}(1)}_X$ gauge boson, the right-handed neutrinos, and the ${\mathrm{U}(1)}_X$ Higgs boson are fixed. Focusing on the case that the ${\mathrm{U}(1)}_X$ gauge symmetry is mostly oriented towards the SM ${\mathrm{U}(1)}_Y$ direction, we investigate a consistency between the inflationary predictions and the latest LHC Run 2 results on the search for a narrow resonance with the dilepton final state. In addition, the inflection-point inflation provides a unique prediction for the running of the spectral index $\alpha \simeq -2.7\times {10}^{-3}{(\frac{60}{N})}^2$ ($N$ is the e-folding number), which can be tested in the near future.

In this paper, we attempt to build a unified model with the democratic texture, that has some unification between up-type Yukawa interactions $Y_{\nu }$ and $Y_u$. Since the $S_{3L}\times S_{3R}$ flavor symmetry is chiral, the unified gauge group is assumed to be Pati-Salam type $SU(4{)}_c\times SU(2{)}_L\times SU(2{)}_R$. The breaking scheme of the flavor symmetry is considered to be $S_{3L}\times S_{3R}\to S_{2L}\times S_{2R}\to 0$. In this picture, the four-zero texture is desirable for realistic masses and mixings. This texture is realized by a specific representation for the second breaking of the $S_{3L}\times S_{3R}$ flavor symmetry. Assuming only renormalizable Yukawa interactions, type-I seesaw mechanism, and neglecting $CP$ phases for simplicity, the right-handed neutrino mass matrix $M_R$ can be reconstructed from low energy input values. Numerical analysis shows that the texture of $M_R$ basically behaves like the “waterfall texture.” Since $M_R$ tends to be the “cascade texture” in the democratic texture approach, a model with type-I seesaw and up-type Yukawa unification $Y_{\nu }\simeq Y_u$ basically requires fine-tunings between parameters. Therefore, it seems to be more realistic to consider universal waterfall textures for both $Y_f$ and $M_R$, e.g., by the radiative mass generation or the Froggatt-Nielsen mechanism. Moreover, analysis of eigenvalues shows that the lightest mass eigenvalue $M_{R1}$ is too light to achieve successful thermal leptogenesis. Although the resonant leptogenesis might be possible, it also requires fine-tunings of parameters.

We analyze the lepton flavor-violating (LFV) Higgs decay $h\to \tau \mu$ in three supersymmetric models: the minimal supersymmetric Standard Model, supersymmetric seesaw model, and supersymmetric $B-L$ model with inverse seesaw (BLSSM-IS). We show that it is not possible to enhance $\mathrm{BR}(h\to \tau \mu )$ without violating the experimental bound on the $\mathrm{BR}(\tau \to \mu \gamma )$ in the generic minimal supersymmetric Standard Model, with nonuniversal slepton masses and/or trilinear couplings. In the supersymmetric seesaw model, where flavor mixing is radiatively generated, the LFV process $\mu \to e\gamma$ strongly constrains the parameter space, and the maximum value of $\mathrm{BR}(h\to \tau \mu )$ is of order ${10}^{-10}$, which is much smaller than the recent results reported by the CMS and ATLAS experiments. On the other hand, in the BLSSM-IS with universal soft supersymmetry-breaking terms defined at the grand unified scale, $\mathrm{BR}(h\to \tau \mu )$ can be accommodated in a wide region of the parameter space without violating LFV constraints. Even though the background processes in the LHC have very small cross sections, we also analyze the possible signal within the BLSSM-IS over the relevant background processes and show that a signal can be extracted. The analysis shows that confirmation of the LFV Higgs boson decay reported by CMS and ATLAS would favor the BLSSM-IS class of models.

We present a calculation of the leptonic decay-constant ratio $f_K/f_{\pi }$ in $2+1$ flavor QCD. Our data set includes five lattice spacings and pion masses reaching down below the physical one. Special emphasis is placed on a careful study of all systematic uncertainties, especially the continuum extrapolation. Our result is perfectly compatible with the first-row unitarity constraint of the Standard Model.

We report the measurement of quark number susceptibilities (QNS) and their temperature dependence from simulations of QCD with two flavors of light dynamical staggered quarks at finite temperature on $8\times 32^3$ lattices. From the radius of convergence of the Taylor expansion we estimate the critical end point. We use a Padé approximant to resum the series expansion and compute the equation of state at finite chemical potential, namely the baryon number density and its contribution to the pressure. We also report the isothermal compressibility of QCD matter at finite baryon density. Finally we explore the freeze-out conditions for a measure of fluctuations. We examine some sources of systematic and statistical errors in all of these measurements.

The constituent quark model with color-spin hyperfine potential is used to investigate the property of a compact pentaquark configuration with $J^p=3/2^{-}$ and $\text{isospin}=1/2$, which is the most likely quantum number of one of the recently observed exotic baryon states at LHCb. Starting from the characterization of the isospin, color, and spin states for the pentaquark configuration, we construct the total wave function composed of the spatial wave function, which we take to be symmetric and in S wave, and the four orthogonal $\text{isospin}\otimes \text{color}\otimes \text{spin}$ states that satisfy the Pauli principle. We then use the variational method to find a compact stable configuration. While there are compact configurations where the hyperfine potential is more attractive than the sum of $p$ and $J/\psi$ hyperfine potentials, we find that the ground state is the isolated $p$ and $J/\psi$ state. Furthermore, the mass of the excited state lies far above the observed pentaquark state leading us to conclude that the observed states cannot be a compact configuration with $J^p=3/2^{-}$, generated by the conventional two-body quark interactions.

The higher derivative corrections in double field theory are revisited to first order in ${\alpha }^{\prime }$. In first order perturbation theory around flat space, the gauge algebra is ${\alpha }^{\prime }$ corrected, governed by two parameters $a$, $b$. One parameter choice corresponds to bosonic string theory, another to heterotic string theory. These results are generalized to second order in perturbation theory by a Noether procedure. Using consistency conditions derived from the Jacobi identity, it is shown that for general $a$, $b$ there is no generalized metric formulation. A manifestly background-independent formulation is instead given by a frame formalism, with ${\alpha }^{\prime }$-deformed frame transformations, as proposed by Marques and Nunez. Their construction is slightly generalized to an ${\alpha }^{\prime }$-deformed $GL(D)\times GL(D)$ frame formalism. The perturbation theory around flat space is matched to second order with the results obtained by the Noether procedure. We also obtain a formulation based on the “nonsymmetric” metric $\mathcal{E}$, the sum of metric, and $b$ field. The transformations of $\mathcal{E}$ under $O(D,D)$ receive nontrivial ${\alpha }^{\prime }$ corrections, unless $a=-b$, in which case there is a generalized metric formulation, in agreement with previous results in the literature.

We describe a Horava-Lifshitz-like reformulated four-fermion Gross-Neveu model describing the dynamics of two-component spinors in ($2+1$)-dimensional space-time. Within our study, we introduce the Lagrange multiplier, study the gap equation (including the finite temperature case) which turns out to display essentially distinct behaviors for even and odd values of the critical exponent $z$, and show that the dynamical parity breaking occurs only for the odd $z$. We demonstrate that for any odd $z$, there exists a critical temperature at which the dynamical parity breaking disappears. Besides of this, we obtain the effective propagator and show that the resulting effective theory is renormalizable within the framework of the $\frac{1}{N}$ expansion for all values of $z$. As one more application of the dynamical parity breaking, we consider coupling of the vector field to the fermions in the case of a simplified spinor-vector coupling and discuss the generation of the Chern-Simons term.

The renormalization group functions for six dimensional scalar ${\varphi }^3$ theory with an $F_4$ symmetry are provided at four loops in the modified minimal subtraction ($\overline{\mathrm{MS}}$) scheme. Aside from the anomalous dimension of $\varphi$ and the $\beta$-function this includes the mass operator and a ${\varphi }^2$-type operator. The anomalous dimension of the latter is computed explicitly at four loops for the $\mathbf{26}$ and $\mathbf{324}$ representations of $F_4$. The $\epsilon$ expansion of all the related critical exponents are determined to $O({\epsilon }^4)$. For instance the value for ${\mathrm{\Delta }}_{\varphi }$ agrees with recent conformal bootstrap estimates in 5 and 5.95 dimensions. The renormalization group functions are also provided at four loops for the group $E_6$.

We study the three-dimensional $U(N)$ Gross-Neveu and $C{P}^{N-1}$ models in the canonical formalism with fixed $U(1)$ charge. For large $N$, this is closely related to coupling the models to Abelian Chern-Simons fields in a monopole background. We show that the presence of the imaginary chemical potential for the $U(1)$ charge makes the phase structure of the models remarkably similar. We calculate their respective large $N$ free energy densities and show that they are mapped into each other in a precise way. Intriguingly, the mapping of the free energies involves the Bloch-Wigner function and its generalizations introduced by Zagier. We expect that our results are connected to the recently discussed 3d bosonization.

Massive spin-2 particles have been a subject of great interest in current research. If the graviton has a small mass, the gravitational force at large distances decreases more rapidly, which could contribute to the explanation of the accelerated expansion of the Universe. The massive spin-2 particles are commonly described by the known Fierz-Pauli action which is formulated in terms of a symmetric tensor $h_{\mu \nu }=h_{\nu \mu }$. However, the Fierz-Pauli theory is not the only possible description of massive spin-2 particles via a rank-2 tensor. There are other two families of models $\mathcal{L}(a_1)$ and ${\mathcal{L}}_{nFP}(c)$, where $a_1$ and $c$ are real arbitrary parameters, which describe massive particles of spin-2 in the flat space via a nonsymmetric tensor $e_{\mu \nu }\ne e_{\nu \mu }$. In the present work we derive Lagrangian constraints stemming from $\mathcal{L}(a_1)$ and ${\mathcal{L}}_{nFP}(c)$ in curved backgrounds with nonminimal couplings which are analytic functions of $m^2$. We show that the constraints lead to a correct counting of degrees of freedom if nonminimal terms are included with fine-tuned coefficients and the background space is of the Einstein type, very much like the Fierz-Pauli case. We also examine the existence of local symmetries.