We provide type IIB string embeddings of two axion variants of natural inflation. We use a combination of RR 2-form axions as the inflaton field and have its potential generated by nonperturbative effects in the superpotential. Besides giving rise to inflation, the models developed take into account the stabilization of the compact space, an essential condition for any semirealistic model of string inflation.

We argue a scenario motivated by the context of string landscape, where our Universe is produced by a new vacuum bubble embedded in an old bubble and these bubble universes have not only different cosmological constants, but also their own different gravitational constants. We study these effects on the primordial curvature perturbations. In order to construct a model of varying gravitational constants, we use the Jordan-Brans-Dicke theory where different expectation values of scalar fields produce difference of constants. In this system, we investigate the nucleation of the bubble universe and the dynamics of the wall separating two spacetimes. In particular, the primordial curvature perturbation on superhorizon scales can be affected by the wall trajectory as the boundary effect. We show how the gravitational constant in the exterior bubble universe modifies the power spectrum, that provides a peak like a bump feature at a large scale.

We construct equilibrium configurations of uniformly rotating neutron stars for selected relativistic mean-field nuclear matter equations of state (EOS). We compute, in particular, the gravitational mass ($M$), equatorial ($R_{\text{eq}}$) and polar ($R_{\text{pol}}$) radii, eccentricity, angular momentum ($J$), moment of inertia ($I$) and quadrupole moment ($M_2$) of neutron stars stable against mass shedding and secular axisymmetric instability. By constructing the constant frequency sequence $f=716\mathrm{Hz}$ of the fastest observed pulsar, PSR J1748–2446ad, and constraining it to be within the stability region, we obtain a lower mass bound for the pulsar, $M_{\min }=[1.2–1.4]M_{\odot }$, for the EOS employed. Moreover, we give a fitting formula relating the baryonic mass ($M_b$) and gravitational mass of nonrotating neutron stars, $M_b/M_{\odot }=M/M_{\odot }+(13/200)(M/M_{\odot }{)}^2$ [or $M/M_{\odot }=M_b/M_{\odot }-(1/20)(M_b/M_{\odot }{)}^2$], which is independent of the EOS. We also obtain a fitting formula, although not EOS independent, relating the gravitational mass and the angular momentum of neutron stars along the secular axisymmetric instability line for each EOS. We compute the maximum value of the dimensionless angular momentum, $a/M\equiv cJ/(G{M}^2)$ (or “Kerr parameter”), $(a/M{)}_{\max }\approx 0.7$, found to be also independent of the EOS. We then compare and contrast the quadrupole moment of rotating neutron stars with the one predicted by the Kerr exterior solution for the same values of mass and angular momentum. Finally, we show that, although the mass quadrupole moment of realistic neutron stars never reaches the Kerr value, the latter is closely approached from above at the maximum mass value, as physically expected from the no-hair theorem. In particular, the stiffer the EOS, the closer the mass quadrupole moment approaches the value of the Kerr solution.

We propose a novel method for probing sleptons in compressed spectra at hadron colliders. The process under study is slepton pair production in $R$-parity conserving supersymmetry, where the slepton decays to a neutralino lightest supersymmetric particle of mass close to the slepton mass. In order to pass the trigger and obtain large missing energy, an energetic monojet is required. Both leptons need to be detected in order to suppress large standard model backgrounds with one charged lepton. We study variables that can be used to distinguish the signal from the remaining major backgrounds, which include $t\overline{t}$, $WW+\text{jet}$, $Z+\text{jet}$, and single top production. We find that the dilepton $m_{T2}$, bound by the mass difference, can be used as an upper bound to efficiently reduce the backgrounds. It is estimated that sleptons with masses up to about 150 GeV can be discovered at the 14 TeV LHC with $100{\mathrm{fb}}^{-1}$ integrated luminosity.

We show that the $2.4\sigma$ signal of the leptonic flavor violating (LFV) Higgs boson decay $h\to \mu \tau$, as observed by the CMS Collaboration recently, can be explained by a certain class of two-Higgs doublet models that allow controllable flavor-changing neutral current with a minimal number of free parameters. We postulate that (i) the alignment limit is maintained, which means the lightest neutral scalar ($h$) has identical couplings to that of the Standard Model Higgs boson and (ii) the signal comes from two other neutral scalars, the $CP$-even $H$ and the -odd $A$, almost degenerate with $h$ at 125 GeV. We also show that (i) it is entirely possible that these scalars are hidden, apart from this LFV signal; (ii) the signal strengths of $b\overline{b}$, ${\tau }^{+}{\tau }^{-}$ and $\gamma \gamma$ around 125 GeV put severe constraints on the parameter space of such models; (iii) the constraint is further enhanced by the nonobservation of processes like $\mu \to e\gamma$, and we predict that the branching ratio of $\mu \to e\gamma$ cannot be even an order below the present experimental limit, highlighting the role it plays in forcing $H$ and $A$ to be near-degenerate; (iv) an enhancement in the ${\tau }^{+}{\tau }^{-}$ production cross section at around 125 GeV is expected in the gluon fusion channel, and should be observed during the next run of the LHC; (v) the branching ratio in the $e\tau$ channel is enhanced and is expected to be at least about 2%. The constrained parameter space and minimum number of free parameters, along with such strong predictions, make this model easily testable and falsifiable.

We propose the supersymmetric Standard Models (SSMs) with a pseudo-Dirac gluino from hybrid $F$- and $D$-term supersymmetry (SUSY) breaking. Similar to the SSMs before the LHC, all the supersymmetric particles in the minimal SSM obtain the SUSY breaking soft terms from the traditional gravity mediation and have masses within about 1 TeV except gluino. To evade the LHC SUSY search constraints, the gluino also has a heavy Dirac mass above 3 TeV from $D$-term SUSY breaking. Interestingly, such a heavy Dirac gluino mass will not induce the electroweak fine-tuning problem. We realize such SUSY breaking via an anomalous $U(1{)}_X$ gauge symmetry inspired from string models. To maintain the gauge coupling unification and increase the Higgs boson mass, we introduce extra vectorlike particles. We study the viable parameter space which satisfies all the current experimental constraints and present a concrete benchmark point. This kind of model not only preserves the merits of pre-LHC SSMs such as naturalness, dark matter, etc., but also solves the possible problems in the SSMs with Dirac gauginos due to the $F$-term gravity mediation.

We define a new class of $Z^{\prime }$ models with neutral flavor-changing interactions at tree level in the down-quark sector. They are related in an exact way to elements of the quark mixing matrix due to an underlying flavored ${\mathrm{U}(1)}^{\prime }$ gauge symmetry, rendering these models particularly predictive. The same symmetry implies lepton-flavor nonuniversal couplings, fully determined by the gauge structure of the model. Our models allow us to address presently observed deviations from the standard model and specific correlations among the new physics contributions to the Wilson coefficients $C_{9,10}^{(\prime )\ell }$ can be tested in $b\to s{\ell }^{+}{\ell }^{-}$ transitions. We furthermore predict lepton-universality violations in $Z^{\prime }$ decays, testable at the LHC.

We explore a scenario of new physics entering the description of $B\to K^{(*)}\mu \mu$ decay through couplings to the operators ${\mathcal{O}}_{9,10}^{\prime }$, satisfying $C_9^{\prime }=-C_{10}^{\prime }$. From the current data on $\mathcal{B}(B_s\to \mu \mu )$ and $\mathcal{B}(B\to K\mu \mu {)}_{[15,22]{\mathrm{GeV}}^2}$, we obtain constraints on $\mathrm{Re}{C}_{10}^{\prime }$ and $\mathrm{Im}{C}_{10}^{\prime }$ which we then assume to be lepton specific, and find $R_K=\mathcal{B}(B\to K\mu \mu )/\mathcal{B}(B\to K\mu \mu {)}_{[1,6]{\mathrm{GeV}}^2}=0.88(8)$, consistent with the recent value measured at the LHCb. A specific realization of this scenario is the one with a scalar leptoquark state $\mathrm{\Delta }$, in which $C_{10}^{\prime }$ is related to the mass of $\mathrm{\Delta }$ and its Yukawa couplings. We then show that this scenario does not make any significant impact on $B_s-{\overline{B}}_s$ mixing amplitude or on $\mathcal{B}(B\to K\nu \overline{\nu })$. Instead, it can modify $R_{K^{*}}=\mathcal{B}(B\to K^{*}\mu \mu )/\mathcal{B}(B\to K^{*}\mu \mu {)}_{[1,6]{\mathrm{GeV}}^2}$, which will soon be experimentally measured, and we find it to be $R_{K^{*}}=1.11(8)$, while $R_{K^{*}}/R_K=1.27(19)$. A similar ratio of forward-backward asymmetries also becomes lower than in the Standard Model.

We perform a detailed hadron-level study on the sensitivity of Higgs boson pair production via the $W{W}^{*}W{W}^{*}$ channel with the final state $3\ell 2j+\cancel{E}$ at the LHC with the collision energy $\sqrt{S}=14\mathrm{TeV}$ and a future 100 TeV collider. To avoid the huge background from $pp\to ZW+\text{jet}$ processes, we confine to consider the four-lepton patterns: $e^{\pm }{e}^{\pm }{\mu }^{\mp }$ and ${\mu }^{\pm }{\mu }^{\pm }{e}^{\mp }$. We propose a partial reconstruction method to determine the most reliable combination. After that, we examine a few crucial observables which can efficiently discriminate signal and background events, especially we notice that the observable $m_{\mathrm{T}2}$ is very efficient. For the LHC 14 TeV collisions, with an accumulated $3000{\mathrm{fb}}^{-1}$ data set, we find that the sensitivity of this mode can reach up to $1.5\sigma$ for the Standard Model and the triple coupling of Higgs boson ${\lambda }_3$ in the simplest effective theory can be constrained into the range [$-1$, 8] at 95% confidence level; at a 100 TeV collider with the integrated luminosity $3000{\mathrm{fb}}^{-1}$, the sensitivity can reach up to $13\sigma$ for the Standard Model and we find that all values of ${\lambda }_3$ in the effective theory can be covered up to $3\sigma$ even without optimizing signals. To precisely measure the triple coupling of Higgs boson ${\lambda }_3=1$ of the Standard Model at a 100 TeV collider, by using the invariant mass of three leptons which is robust against the contamination of underlying events and pileup effects and by performing a ${\chi }^2$ analysis, we find that it can be determined into a range [0.8, 1.5] at 95% confidence level.

The study of the spin-parity and tensor structure of the interactions of the recently discovered Higgs boson is performed using the $H\to ZZ,Z{\gamma }^{*},{\gamma }^{*}{\gamma }^{*}\to 4\ell$, $H\to WW\to \ell \nu \ell \nu$, and $H\to \gamma \gamma$ decay modes. The full data set recorded by the CMS experiment during the LHC run 1 is used, corresponding to an integrated luminosity of up to $5.1{\mathrm{fb}}^{-1}$ at a center-of-mass energy of 7 TeV and up to $19.7{\mathrm{fb}}^{-1}$ at 8 TeV. A wide range of spin-two models is excluded at a 99% confidence level or higher, or at a 99.87% confidence level for the minimal gravitylike couplings, regardless of whether assumptions are made on the production mechanism. Any mixed-parity spin-one state is excluded in the $ZZ$ and $WW$ modes at a greater than 99.999% confidence level. Under the hypothesis that the resonance is a spin-zero boson, the tensor structure of the interactions of the Higgs boson with two vector bosons $ZZ$, $Z\gamma$, $\gamma \gamma$, and $WW$ is investigated and limits on eleven anomalous contributions are set. Tighter constraints on anomalous $HVV$ interactions are obtained by combining the $HZZ$ and $HWW$ measurements. All observations are consistent with the expectations for the standard model Higgs boson with the quantum numbers $J^{\mathrm{PC}}=0^{++}$.

We study the Anastasiou–Bern–Dixon–Kosower relation using maximal cuts of one- and two-loop integrals with up to five external legs. We show how to find a special combination of integrals that allows the relation to exist, and how to reconstruct the terms with one-loop integrals squared. The reconstruction relies on the observation that integrals across different loop orders can have support on the same generalized unitarity cuts and can share global poles. We discuss the appearance of nonhomologous integration contours in multivariate residues. Their origin can be understood in simple terms, and their existence enables us to distinguish contributions from different integrals. Our analysis suggests that maximal and near-maximal cuts can be used to infer the existence of integral identities more generally.

The framework of nonrelativistic effective field theory (NREFT) aims to generalize the standard analysis of direct detection experiments in terms of spin-dependent and spin-independent interactions. We show that a number of NREFT operators lead to distinctive new directional signatures, such as prominent ringlike features in the directional recoil rate, even for relatively low-mass weakly interacting massive particles. We discuss these signatures and how they could affect the interpretation of future results from directional detectors. We demonstrate that considering a range of possible operators introduces a factor of 2 uncertainty in the number of events required to confirm the median recoil direction of the signal. Furthermore, using directional detection, it is possible to distinguish the more general NREFT interactions from the standard spin-indenpendent/spin-dependent interactions at the $2\sigma$ level with $\mathcal{O}(100–500)$ events. In particular, we demonstrate that for certain NREFT operators directional sensitivity provides the only method of distinguishing them from these standard operators, highlighting the importance of directional detectors in probing the particle physics of dark matter.

The low-mass X-ray binary Scorpius X-1 (Sco X-1) is potentially the most luminous source of continuous gravitational-wave radiation for interferometers such as LIGO and Virgo. For low-mass X-ray binaries this radiation would be sustained by active accretion of matter from its binary companion. With the Advanced Detector Era fast approaching, work is underway to develop an array of robust tools for maximizing the science and detection potential of Sco X-1. We describe the plans and progress of a project designed to compare the numerous independent search algorithms currently available. We employ a mock-data challenge in which the search pipelines are tested for their relative proficiencies in parameter estimation, computational efficiency, robustness, and most importantly, search sensitivity. The mock-data challenge data contains an ensemble of 50 Scorpius X-1 (Sco X-1) type signals, simulated within a frequency band of 50–1500 Hz. Simulated detector noise was generated assuming the expected best strain sensitivity of Advanced LIGO [1] and Advanced VIRGO [2] ($4\times {10}^{-24}{\mathrm{Hz}}^{-1/2}$). A distribution of signal amplitudes was then chosen so as to allow a useful comparison of search methodologies. A factor of 2 in strain separates the quietest detected signal, at $6.8\times {10}^{-26}$ strain, from the torque-balance limit at a spin frequency of 300 Hz, although this limit could range from $1.2\times {10}^{-25}$ (25 Hz) to $2.2\times {10}^{-26}$ (750 Hz) depending on the unknown frequency of Sco X-1. With future improvements to the search algorithms and using advanced detector data, our expectations for probing below the theoretical torque-balance strain limit are optimistic.

We revisit a simple model that combines minimal gauge mediation and the next-to-minimal supersymmetric standard model. We show that one can obtain a 125 GeV Standard Model–like Higgs boson with top squarks as light as 1.1 TeV, thanks to the mixing of the Higgs with a singlet state at $\mathcal{O}(90–100)\mathrm{GeV}$. Sparticle searches at the LHC may come with additional $b$ jets or taus and may involve displaced vertices. The sparticle production cross section at the 13 TeV LHC can be $\mathcal{O}(10–100)\mathrm{fb}$, leading to great prospects for discovery in the early phase of LHC run II.

A fermion dark matter candidate with a relic abundance set by annihilation through a pseudoscalar can evade constraints from direct detection experiments. We present simplified models that realize this fact by coupling a fermion dark sector to a two-Higgs doublet model. These models are generalizations of mixed bino-Higgsino dark matter in the minimal supersymmetric standard model, with more freedom in the couplings and scalar spectra. Annihilation near a pseudoscalar resonance allows a significant amount of parameter space for thermal relic dark matter compared to singlet-doublet dark matter, in which the fermions couple only to the standard model (SM) Higgs doublet. In a general two-Higgs doublet model, there is also freedom for the pseudoscalar to be relatively light and it is possible to obtain thermal relic dark matter candidates even below 100 GeV. In particular, we find ample room to obtain dark matter with mass around 50 GeV and fitting the Galactic center excess in gamma-rays. This region of parameter space can be probed by LHC searches for heavy pseudoscalars or electroweakinos, and possibly by other new collider signals.

We perform a dispersive analysis of the $\omega \pi$ electromagnetic transition form factor, using as input the discontinuity provided by unitarity below the $\omega \pi$ threshold and including for the first time experimental data on the modulus measured from $e^{+}{e}^{-}\to \omega {\pi }^0$ at higher energies. The input leads to stringent parametrization-free constraints on the modulus of the form factor below the $\omega \pi$ threshold, which are in disagreement with some experimental values measured from $\omega \to {\pi }^0{\gamma }^{*}$ decay. We discuss the dependence on the input parameters in the unitarity relation, using for illustration an $N/D$ formalism for the P partial wave of the scattering process $\omega \pi \to \pi \pi$, improved by a simple prescription which simulates the rescattering in the crossed channels. Our results confirm the existence of a conflict between experimental data and theoretical calculations of the $\omega \pi$ form factor in the region around 0.6 GeV and bring further arguments in support of renewed experimental efforts to measure more precisely the $\omega \to {\pi }^0{\gamma }^{*}$ decay.

We have demonstrated the viability of using the Laser Ranging Interferometer on the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) space mission to test key aspects of the interspacecraft interferometry proposed for detecting gravitational waves. The Laser Ranging Interferometer on GRACE-FO will be the first demonstration of interspacecraft interferometry. GRACE-FO shares many similarities with proposed space-based gravitational wave detectors based on the Laser Interferometer Space Antenna (LISA) concept. Given these similarities, GRACE-FO provides a unique opportunity to test novel interspacecraft interferometry techniques that a LISA-like mission will use. The LISA Experience from GRACE-FO Optical Payload (LEGOP) is a project developing tests of arm locking and time delay interferometry (TDI), two frequency stabilization techniques, that could be performed on GRACE-FO. In the proposed LEGOP TDI demonstration one GRACE-FO spacecraft will have a free-running laser while the laser on the other spacecraft will be locked to a cavity. It is proposed that two one-way interspacecraft phase measurements will be combined with an appropriate delay in order to produce a round-trip, dual one-way ranging (DOWR) measurement independent of the frequency noise of the free-running laser. This paper describes simulated and experimental tests of a tone-assisted TDI ranging (TDIR) technique that uses a least-squares fitting algorithm and fractional-delay interpolation to find and implement the delays needed to form the DOWR TDI combination. The simulation verifies tone-assisted TDIR works under GRACE-FO conditions. Using simulated GRACE-FO signals the tone-assisted TDIR algorithm estimates the time-varying interspacecraft range with a rms error of $\pm 0.2\mathrm{m}$, suppressing the free-running laser frequency noise by 8 orders of magnitude. The experimental results demonstrate the practicability of the technique, measuring the delay at the 6 ns level in the presence of a significant displacement signal.

Misner spacetime is among the simplest solutions of Einstein’s equation that exhibits a Cauchy horizon with a smooth extension beyond it. Besides violating strong cosmic censorship, this extension contains closed timelike curves. We analyze the stability of the Cauchy horizon and prove that neighboring spacetimes in one parameter families of solutions through Misner’s in pure gravity, gravity coupled to a scalar field, or Einstein-Maxwell theory end at the Cauchy horizon developing a curvature singularity.

We investigate which Jordan frame $F(R)$ gravity can describe a type IV singular bouncing cosmological evolution, with special emphasis given near the point at which the type IV singularity occurs. The cosmological bounce is chosen in such a way that the bouncing point coincides exactly with the type IV singularity point. The stability of the resulting $F(R)$ gravity is examined and in addition, we study the Einstein frame scalar-tensor theory counterpart of the resulting Jordan frame $F(R)$ gravity. Also, by assuming that the Jordan frame metric is chosen in such a way so that, when conformally transformed in the Einstein frame, it yields a quasi–de Sitter or de Sitter–Friedmann–Robertson–Walker metric, we study the observational indexes which turn out to be consistent with Planck 2015 data in the case of the Einstein frame scalar theory. Finally, we study the behavior of the effective equation of state corresponding to the type IV singular bounce and after we compare the resulting picture with other bouncing cosmologies, we critically discuss the implications of our analysis.

The relativistic generalization of the Newtonian Lagrangian perturbation theory is investigated. In previous works, the first-order trace solutions that are generated by the spatially projected gravitoelectric part of the Weyl tensor were given together with extensions and applications for accessing the nonperturbative regime. We furnish here construction rules to obtain from Newtonian solutions the gravitoelectric class of relativistic solutions, for which we give the complete perturbation and solution schemes at any order of the perturbations. By construction, these schemes generalize the complete hierarchy of solutions of the Newtonian Lagrangian perturbation theory.