Hybrid stars with a quark phase described by the Nambu-Jona-Lasinio model are studied. The hadron-quark model used to determine the stellar matter equation of state favors the appearance of quark matter: the coincidence of the deconfinement and chiral transitions and a low vacuum constituent quark mass. These two properties are essential to build equations of state that predict pure quark matter in the center of neutron stars. The effect of vector-isoscalar and vector-isovector terms is discussed, and it is shown that the vector-isoscalar terms are necessary to describe $2M_{\odot }$ hybrid stars, and the vector-isovector terms result in larger quark cores and a smaller deconfinement density.

We derive analyticity constraints on a nonlinear ghost-free effective theory of a massive spin-2 particle known as pseudolinear massive gravity, and on a generalized theory of a massive spin-1 particle, both of which provide simple IR completions of Galileon theories. For pseudolinear massive gravity we find that, unlike de Rham, Gabadadze, and Tolley massive gravity, there is no window of parameter space which satisfies the analyticity constraints. For massive vectors which reduce to Galileons in the decoupling limit, we find that no two-derivative actions are compatible with positivity but that higher derivative actions can be made compatible.

We study charge and energy diffusion in simple holographic theories with broken translational symmetry. We find that when the effects of momentum relaxation are very strong the diffusion constants take universal values $D_c\sim D_e\sim \hslash v_B^2/(k_{B}T)$. Here $v_B$ is the velocity of the butterfly effect and the coefficients of proportionality depend only on the scaling exponents of the infra-red fixed point. Our results suggest that diffusion in these incoherent black holes is controlled by $\tau \sim \hslash /(k_{B}T)$ independently of the mechanism of momentum relaxation.

By using the worldline approach to quantum field theory, we demonstrate to all orders that the sources of a quantum field theory over ${\text{Mink}}_4$ naturally form a field theory over ${\mathrm{AdS}}_5$. In particular, this holds for higher-spin sources of a free scalar theory. We work entirely within quantum-field theory and do not select a subset of diagrams. As the auxiliary fifth dimension Schwinger’s proper time is grouped with the physical four spacetime dimensions into an ${\mathrm{AdS}}_5$ geometry. The four-dimensional sources are extended to five-dimensional fields by a Wilson flow (gradient flow). A variational principle for said flow reproduces the corresponding holographic computation.

Traditional Bell’s argument shows that freedom of choice is inconsistent with quantum realism if lack of signaling and sufficiently fast choices and readouts are assumed. While no-signaling alone is a consequence of special relativity, this is not the case of spacetime location of choice and readout. Here we attempt to incorporate freedom of choice into quantum objective realism relying solely on relativistic quantum field theory. We conclude that this is impossible without breaking relativistic invariance and put forward the possibility of signaling faster than light, which cannot be excluded if an ultimate theory violates relativity.

Observational evidence for dark matter is limited to gravitational effects. Dedicated searches have yielded null results, challenging the most popular models. This can be explained if cold dark matter is a massive spin-2 particle and, thus, a manifestation of gravity itself. In the unique consistent theory for a massless and a massive spin-2 field, the latter can be heavy, stable on cosmological scales, and produced with correct abundance, and its matter coupling is naturally as weak as the gravitational one. The theory satisfies current gravity tests, and we suggest several gravitational signatures.

Scalar dark energy fields that couple to the standard model can give rise to observable signatures at the LHC. In this work, we show that $t\overline{t}+\mathrm{missing}$ energy and monojet searches are suitable probes in the limit where the dark energy scalar is stable on collider distances. We discuss the prospects of distinguishing the dark energy character of new physics signals from dark matter signatures and the possibility of probing the self-interactions of the dark energy sector.

We develop and study the position-dependent bispectrum. It is a generalization of the recently proposed position-dependent power spectrum method of measuring the squeezed-limit bispectrum. The position-dependent bispectrum can similarly be used to measure the squeezed-limit trispectrum in which one of the wavelengths is much longer than the other three. In this work, we will mainly consider the case in which the three smaller wavelengths are nearly the same (the equilateral configuration). We use the Fisher information matrix to forecast constraints on bias parameters and the amplitude of primordial trispectra from the position-dependent bispectrum method. We find that the method can constrain the local-type $g_{\mathrm{NL}}$ at a level of $\sigma (g_{\mathrm{NL}}^{\text{local}})\approx 3\times 10^5$ for a large volume SPHEREx-like survey; improvements can be expected by including all the triangular configurations of the bispectra rather than just the equilateral configuration. However, the same measurement would also constrain a much larger family of trispectra than local $g_{\mathrm{NL}}$ model. We discuss the implications of the forecasted reach of future surveys in terms of super cosmic variance uncertainties from primordial non-Gaussianities.

Debate persists as to whether the cosmological constant $\mathrm{\Lambda }$ can directly modify the power of a gravitational lens. With the aim of reestablishing a consensus on this issue, I conduct a comprehensive analysis of gravitational lensing (to second order) in the Schwarzschild–de Sitter spacetime, wherein the effects of $\mathrm{\Lambda }$ should be most apparent. To second order, the effective lensing law is found to be in precise agreement with the $\mathrm{\Lambda }=0$ result: ${\alpha }_{\mathrm{eff}}=4m/b_{\mathrm{eff}}+15\pi m^2/4b_{\mathrm{eff}}^2+O(m^3/b_{\mathrm{eff}}^3)$, where the effective bending angle ${\alpha }_{\mathrm{eff}}$ and impact parameter $b_{\mathrm{eff}}$ are defined by the angles and angular diameter distances measured by a comoving cosmological observer. [These observers follow the timelike geodesic congruence which (i) respects the continuous symmetries of the spacetime and (ii) approaches local isotropy most rapidly far from the lens.] The effective lensing law can be derived using lensed or unlensed angular diameter distances, although the inherent ambiguity of unlensed distances generates an additional uncertainty $O(m^5/\mathrm{\Lambda }{b}_{\mathrm{eff}}^7)$. These calculations do not rule out the possibility of an extremely small $\mathrm{\Lambda }$-lensing effect $O(m^3/b_{\mathrm{eff}}^3)$; however, such an effect would be completely negligible in practice and will always be smaller than the uncertainty from unlensed distances. I conclude that, despite recent legitimate corrections to the formalism, the cosmological constant does not interfere with gravitational lensing in any practical way.

The $CPT$-even sector of the standard model extension amounts to extending Maxwell electrodynamics by a gauge invariant term of the form $-\frac{1}{4}(k_F{)}_{\alpha \beta \mu \nu }{F}^{\alpha \beta }{F}^{\mu \nu }$, where the Lorentz-violating (LV) background tensor $(k_F{)}_{\alpha \beta \mu \nu }$ possesses the symmetries of the Riemann tensor. The electrodynamics in ponderable media is still described by Maxwell equations in matter with modified constitutive relations which depend on the coefficients for Lorentz violation. We study the effects of this theory on the Casimir force between two semi-infinite ponderable media. The Fresnel coefficients characterizing the vacuum-medium interface are derived, and with the help of these, we compute the Casimir energy density. At leading order in the LV coefficients, the Casimir energy density is numerically evaluated and successfully compared with the standard result. We also found a variety of intriguing effects, such as a nontrivial Kerr effect and the Casimir effect between two phases of the electromagnetic vacuum. We consider a bubble of Lorentz-symmetric (Maxwell) vacuum embedded in the infinite Lorentz-violating vacuum, and we calculate the Casimir energy at leading order, which in this case is quadratic in the LV coefficients. The Casimir force can be positive, zero, or negative, depending on the relative strengths between the LV coefficients.

We investigate both the chiral and deconfinement phase transitions of QCD matter in a refined scheme of Dyson-Schwinger equations, which have been shown to be successful in giving the meson mass spectrum and matching the interaction with the results from ab initio computation. We verify the equivalence of the chiral susceptibility criterion with different definitions for the susceptibility and confirm that the chiral susceptibility criterion is efficient to fix not only the chiral phase boundary but also the critical end point (CEP), especially when one could not have the effective thermodynamical potential. We propose a generalized Schwinger function criterion for the confinement. We give the phase diagram of both phase transitions and show that in the refined scheme the position of the CEP shifts to lower chemical potential and higher temperature. Based on our calculation and previous results of the chemical freeze-out conditions, we propose that the CEP is located in the states of the matter generated by the Au–Au collisions with $\sqrt{s_{NN}}=9–15\mathrm{GeV}$.

Kinetic mixing is a fundamental property of models with a gauge symmetry involving several U(1) group factors. In this paper, we perform a numerical study of the impact of kinetic mixing on beta functions at two-loop. To do so, we use the recently published PyR@TE 2 software to derive the complete set of renormalization group equations of the standard model B-L model at two-loop including kinetic mixing. We show that it is important to properly account for kinetic mixing as the evolution of the parameters with the energy scale can change drastically. In some cases, these modifications can even lead to a different conclusion regarding the stability of the scalar potential.

We provide complete one-loop predictions for the direct production of the neutralino pairs via photon-photon collisions which appears for the first time at one-loop level in the minimal supersymmetric standard model at the International Linear Collider. We present a comprehensive investigation of the dependence of total cross section on the center-of-mass energy and the $\tan \beta$ for three different scenarios based on gaugino/Higgsino fractions of the neutralinos. Furthermore, by investigating the behavior with the most relevant parameters $\mu$ and $M_2$, we exhibit regions of the parameter space where the enhancement of the cross section is large enough to be detectable at linear colliders. Our analysis shows that the corresponding production cross section reaches its highest values when the lightest neutralino ${\tilde{\chi }}_1^0$ has a dominant Higgsino component and/or the next-to-lightest neutralino ${\tilde{\chi }}_2^0$ has a dominant gaugino component.

We present a class of left-right symmetric models where Dirac as well as Majorana mass terms of neutrinos can arise at the one-loop level in a scotogenic fashion: with dark matter particles going inside the loop. We show the possibility of naturally light right-handed neutrinos that can have interesting implications for neutrinoless double beta decay experiments as well as cosmology. Apart from a stable dark matter candidate stabilized by a remnant $Z_2$ symmetry, one can also have a long-lived keV sterile neutrino dark matter in these models. This class of models can have very different collider signatures compared to the conventional left-right models.

We calculate the $\mathcal{O}({\alpha }_s)$ QCD corrections to the inclusive $h\to b\overline{b}$ decay rate in the dimension-6 standard model effective field theory (SMEFT). The QCD corrections multiplying the dimension-6 Wilson coefficients which alter the $hb\overline{b}$-vertex at tree-level are proportional to the standard model (SM) ones, so next-to-leading order results can be obtained through a simple rescaling of the tree-level decay rate. On the other hand, contributions from the operators $Q_{bG}$ and $Q_{HG}$, which alter the $gb\overline{b}$-vertex and introduce a $hgg$-vertex respectively, enter at $\mathcal{O}({\alpha }_s)$ and induce sizeable corrections which are unrelated to the SM ones and cannot be anticipated through a renormalization-group analysis. We present compact analytic results for these contributions, which we recommend to be included in future phenomenological studies.

The two-parameter Weibull function is used to describe the charged particle multiplicity distribution in $e^{+}{e}^{-}$ collisions at the highest available energy measured by the TASSO and ALEPH experiments. The Weibull distribution has wide applications in naturally evolving processes based on fragmentation and sequential branching. The Weibull model describes the multiplicity distribution very well, as particle production processes involve QCD parton fragmentation. The effective energy model of particle production was verified using Weibull parameters and the same was used to predict the multiplicity distribution in $e^{+}{e}^{-}$ collisions at future collider energies.

String theory contains few known working examples of de Sitter vacua, four-dimensional universes with a positive cosmological constant. A notorious obstacle is the stabilization of a large number—sometimes hundreds—of moduli fields that characterize the compact dimensions. We study the stability of a class of supersymmetric moduli (the complex structure moduli and dilaton in type-IIB flux compactifications) in the regime where the volume of the compact space is large but not exponentially large. We show that, if the number of moduli is very large, random matrix theory provides a new stability condition, a lower bound on the volume. We find a new class of stable vacua where the mass spectrum of these supersymmetric moduli is gapped, without requiring a large mass hierarchy between moduli sectors or any fine-tuning of the superpotential. We provide the first explicit example of this class of vacua in the ${\mathbb{P}}_{[1,1,1,6,9]}^4$ model. A distinguishing feature is that all fermions in the supersymmetric sector are lighter than the gravitino.

We construct supersymmetric irregular vertex operators of arbitrary rank, appearing in the colliding limit of primary fields. We find that the structure of the supersymmetric irregular vertices differs significantly from the bosonic case: upon supersymmetrization, the irregular operators are no longer the eigenstates of positive Virasoro and $W_N$ generators but block diagonalize them. We relate the block-diagonal structure of the irregular vertices to contributions of the Ramond sector to the colliding limit.

We investigate the backreaction of the quantum fluctuations of a very light ($m\lesssim H_{\text{today}}$) nonminimally coupled spectator scalar field on the expansion dynamics of the Universe. The one-loop expectation value of the energy-momentum tensor of these fluctuations, as a measure of the backreaction, is computed throughout the expansion history from the early inflationary universe until the onset of recent acceleration today. We show that, when the nonminimal coupling $\xi$ to Ricci curvature is negative (${\xi }_c=1/6$ corresponding to conformal coupling), the quantum backreaction grows exponentially during inflation, such that it can grow large enough rather quickly (within a few hundred $e$-foldings) to survive until late time and constitute a contribution of the cosmological constant type of the right magnitude to appreciably alter the expansion dynamics. The unique feature of this model is in that, under rather generic assumptions, inflation provides a natural explanation for the initial conditions needed to explain the late-time accelerated expansion of the Universe, making it a particularly attractive model of dark energy.