Mon·May 4, 2020Monday·May 4, 2020

1. 01*

   Anomalies in ${}^8$Be nuclear transitions and $(g-2{)}_{e,\mu }$: towards a minimal combined explanation

   C. Hati🇩🇪 · J. Kriewald🇫🇷 · J. Orloff🇫🇷 · A. M. Teixeira🇫🇷

   Motivated by a simultaneous explanation of the apparent discrepancies in the light charged lepton anomalous magnetic dipole moments, and the anomalous internal pair creation in ${}^8$Be nuclear transitions, we explore a simple New Physics model, based on an extension of the Standard Model gauge group by a $U(1{)}_{B-L}$. The model further includes heavy vector-like fermion fields, as well as an extra scalar responsible for the low-scale breaking of $U(1{)}_{B-L}$, which gives rise to a light $Z^{\prime }$ boson. The new fields and currents allow to explain the anomalous internal pair creation in ${}^8$Be while being consistent with various experimental constraints. Interestingly, we find that the contributions of the $Z^{\prime }$ and the new $U(1{)}_{B-L}$-breaking scalar can also successfully account for both $(g-2{)}_{e,\mu }$ anomalies; the strong phenomenological constraints on the model's parameter space ultimately render the combined explanation of $(g-2{)}_e$ and the anomalous internal pair creation in ${}^8$Be particularly predictive. The underlying idea of this minimal "prototype model" can be readily incorporated into other protophobic $U(1)$ extensions of the Standard Model.

   hep-phJHEP(2020)·55 citations
2. 02*

   Dimension-8 Operators in the Standard Model Effective Field Theory

   Christopher W. Murphy🇺🇸

   We present a complete basis of dimension-8 operators in the Standard Model Effective Field Theory. Attention is paid to operators that vanish in the absence of flavor structure. There are dimension-8 SMEFT 44,807 operators. We also briefly discuss a few aspects of phenomenology involving dimension-8 operators, including light-by-light scattering and electroweak precision data.

   hep-phJHEP(2020)·327 citations
3. 03*

   Revisiting longitudinal plasmon-axion conversion in external magnetic fields

   Andrea Caputo🇪🇸 · Alexander J. Millar🇸🇪 · Edoardo Vitagliano🇺🇸

   In the presence of an external magnetic field the axion and the photon mix. In particular, the dispersion relation of a longitudinal plasmon always crosses the dispersion relation of the axion (for small axion masses), thus leading to a resonant conversion. Using thermal field theory we concisely derive the axion emission rate, applying it to astrophysical and laboratory scenarios. For the Sun, depending on the magnetic field profile plasmon-axion conversion can dominate over Primakoff production at low energies ($\lesssim 200$eV). This both provides a new axion source for future helioscopes and, in the event of discovery, would probe the magnetic field structure of the Sun. In the case of white dwarfs (WDs), plasmon-axion conversion provides a pure photon coupling probe of the axion, which may contribute significantly for low-mass WDs. Finally we rederive and confirm the axion absorption rate of the recently proposed plasma haloscopes.

   hep-phPRD(2020)·65 citations
4. 04*

   Comparing light-front quantization with instant-time quantization

   Philip D. Mannheim🇺🇸 · Peter Lowdon🇫🇷 · Stanley J. Brodsky🇺🇸

   We compare light-front quantization and instant-time quantization both at the level of operators and at the level of their Feynman diagram matrix elements. At the level of operators light-front quantization and instant-time quantization lead to equal light-front time commutation (or anticommutation) relations that appear to be quite different from equal instant-time commutation (or anticommutation) relations. Despite this we show that at unequal times instant-time and light-front commutation (or anticommutation) relations actually can be transformed into each other, with it only being the restriction to equal times that makes the commutation (or anticommutation) relations appear to be so different. While our results are valid for both bosons and fermions, for fermions there are subtleties associated with tip of the light cone contributions that need to be taken care of. At the level of Feynman diagrams we show for non-vacuum Feynman diagrams that the pole terms in four-dimensional light-front Feynman diagrams reproduce the three-dimensional light-front on-shell Hamiltonian Fock space formulation in which the light-front energy and light-front momentum are on shell. However, because of circle at infinity contributions we show that this equivalence fails for four-dimensional light-front vacuum tadpole diagrams. Then, precisely because of these circle at infinity contributions, light-front vacuum tadpole diagrams are not only nonzero, they are actually equal to instant-time vacuum tadpole diagrams. Light-front vacuum diagrams are not correctly describable by the on-shell Hamiltonian formalism, and thus not by the closely related infinite momentum frame prescription either. With the transformation from instant-time fields to light-front fields being a spacetime translation, not only are instant-time quantization and light-front quantization equivalent, they are unitarily equivalent.

   hep-phhep-thPhys.Rept.(2021)·29 citations
5. 05*

   Kinetic theory with spin: From massive to massless fermions

   Xin-Li Sheng🇨🇳 · Qun Wang🇨🇳 · Xu-Guang Huang🇨🇳

   We find that the recently developed kinetic theories with spin for massive and massless fermions are smoothly connected. By introducing a reference-frame vector, we decompose the dipole-moment tensor into electric and magnetic dipole moments. We show that the axial-vector component of the Wigner function contains a contribution from the transverse magnetic dipole moment which accounts for the transverse spin degree of freedom (DOF) and vanishes smoothly in the massless limit. As a result, the kinetic equations, describing four DOF for massive fermions, becomes smoothly the chiral kinetic equations describing two DOF in the massless limit. We also confirm the small-mass behavior of the Wigner function by explicit calculation using a Gaussian wave packet.

   hep-phhep-thnucl-thPRD(2020)·31 citations
6. 06*

   Massless Limit of Transport Theory for Massive Fermions

   Xingyu Guo🇨🇳

   We studied the $m=0$ limit of different components of Wigner functions for massive fermions. Comparing with the chiral kinetic theory, we separated the vanishing part and non-vanishing part for vector and axial vector components, up to the first order of $\hslash$. Then we discussed the possible physical meaning of the vanishing and non-vanishing parts, and their different behavior at thermal equilibrium.

   hep-phCPC(2020)·24 citations
7. 07*

   Aspects of relativistic heavy-ion collisions

   Georg Wolschin🇩🇪

   The rapid thermalization of quarks and gluons in the initial stages of relativistic heavy-ion collisions is treated using analytic solutions of a nonlinear diffusion equation with schematic initial conditions, and for gluons with boundary conditions at the singularity. On a similarly short time scale of $t\le 1$ fm/$c$, the stopping of baryons is accounted for through a QCD-inspired approach based on the parton distribution functions of valence quarks, and gluons. Charged-hadron production is considered phenomenologically using a linear relativistic diffusion model with two fragmentation sources, and a central gluonic source that rises with ${\ln }^3(s_{NN})$. The limiting-fragmentation conjecture that agrees with data at energies reached at the Relativistic Heavy Ion Collider (RHIC) is found to be consistent with Large Hadron Collider (LHC) data for Pb-Pb at $\sqrt{s_{NN}}=2.76$ and $5.02$ TeV. Quarkonia are used as hard probes for the properties of the quark-gluon plasma (QGP) through a comparison of theoretical predictions with recent CMS, ALICE and LHCb data for Pb-Pb and p-Pb collisions.

   hep-phUniverse(2020)·7 citations
8. 08*

   Compactified Spacelike Extra Dimension & Brane-Higgs Field

   Florian Nortier🇫🇷

   In the paradigm with a small warped Spacelike Extra Dimensions (SED), the Higgs field is in general localized at a boundary of the SED (TeV-brane) where the gravity scale is redshifted to the TeV by a warp factor. If the SM gauge bosons and fermions propagate into the warped SED, one can generate the mass hierarchy for fermions. It is thus crucial to treat carefully the TeV-brane localized masses for such fermions, which is done in the literature by applying a regularization process suffering from a lack of consistency and more importantly being useless, as we demonstrate in detail in the present thesis. The first part of the thesis is devoted to the treatment of brane localized mass terms for 5D fermions, which requires the introduction of new Lagrangian terms at the SED boundaries, similar to the Gibbons-Hawking terms in gravity. The second part consists in applying different methods (function/distribution fields, 4D/5D calculations, etc) to various brane localized terms (kinetic terms, Majorana masses, etc), as well as a generalization to several classified models (flat/warped dimensions, intervalle/orbifold, etc). In the third part, we propose to compactify a flat SED on a star/rose graph with a large number of identical small leaves/petals. We obtain a compactified space with a large volume without a large compactification length to stabilize. We use the approach of 5D fermions to build a toy model of small Dirac neutrino masses (brane localized left-handed neutrinos and bulk right-handed ones).

   hep-phhep-thquant-ph5 citations
9. 09*

   Freeze-in Dark Matter from a Minimal B-L Model and Possible Grand Unification

   Rabindra N. Mohapatra🇺🇸 · Nobuchika Okada🇺🇸

   We show that a minimal local $B-L$ symmetry extension of the standard model can provide a unified description of both neutrino mass and dark matter. In our model, $B-L$ breaking is responsible for neutrino masses via the seesaw mechanism, whereas the real part of the $B-L$ breaking Higgs field (called $\sigma$ here) plays the role of a freeze-in dark matter candidate for a wide parameter range. Since the $\sigma$-particle is unstable, for it to qualify as dark matter, its lifetime must be longer than $10^{25}$ seconds implying that the $B-L$ gauge coupling must be very small. This in turn implies that the dark matter relic density must arise from the freeze-in mechanism. The dark matter lifetime bound combined with dark matter relic density gives a lower bound on the $B-L$ gauge boson mass in terms of the dark matter mass. We point out parameter domains where the dark matter mass can be both in the keV to MeV range as well as in the PeV range. We discuss ways to test some parameter ranges of this scenario in collider experiments. Finally, we show that if instead of $B-L$, we consider the extra $U(1)$ generator to be $-4I_{3R}+3(B-L)$, the basic phenomenology remains unaltered and for certain gauge coupling ranges, the model can be embedded into a five dimensional $SO(10)$ grand unified theory.

   hep-phPRD(2020)·18 citations
10. 10*

    Three Exceptions to the Grossman-Nir Bound

    Robert Ziegler🇩🇪 · Jure Zupan🇺🇸 · Roman Zwicky🇬🇧

    We show that the Grossman-Nir (GN) bound, $\text{Br}(K_L\to {\pi }^0\nu \bar{\nu })\le 4.3\text{Br}(K^{+}\to {\pi }^{+}\nu \bar{\nu })$, can be violated in the presence of light new physics with flavor violating couplings. We construct three sample models in which the GN bound can be violated by orders of magnitude, while satisfying all other experimental bounds. In the three models the enhanced branching ratio $\text{Br}(K_L\to {\pi }^0+\mathrm{inv})$ is due to $K_L\to {\pi }^0{\varphi }_1$, $K_L\to {\pi }^0{\varphi }_1{\varphi }_1$, $K_L\to {\pi }^0{\psi }_1{\bar{\psi }}_1$ transitions, respectively, where ${\varphi }_1({\psi }_1)$ is a light scalar (fermion) that escapes the detector. In the three models $\text{Br}(K^{+}\to {\pi }^{+}+\mathrm{inv})$ remains very close to the SM value, while $\text{Br}(K_L\to {\pi }^0+\mathrm{inv})$ can saturate the present KOTO bound. Besides invisible particles in the final state (which may account for dark matter) the models require additional light mediators around the GeV-scale.

    hep-phJHEP(2020)·25 citations
11. 11*

    Fast Neutrino Flavor Conversion at Late Time

    Soumya Bhattacharyya (TIFR Mumbai)🇮🇳 · Basudeb Dasgupta (TIFR Mumbai)🇮🇳

    We study the fully nonlinear fast flavor evolution of neutrinos in 1+1 dimensions. Our numerical analysis shows that at late time the system reaches an approximately steady state. Using the steady state approximation we analytically show that the spatial variation of the polarization vectors is given by their precession around a common axis, which itself has a motion reminiscent of a gyroscopic pendulum. We then show that the steady state solution to the equations of motion cannot be separated in position and velocity, that is the motion is not collective in the usual sense. However, the fast evolution allows spectral-swap-like dynamics leading to partial decoherence over a range of velocities, constrained by conservation of lepton number(s). Finally, we numerically show that at late time the transverse components of the polarization vectors become randomly oriented at different spatial locations for any velocity mode and lepton asymmetry.

    hep-phPRD(2020)·79 citations
12. 12*

    Revisiting supernova constraints on a light CP-even scalar

    P. S. Bhupal Dev🇺🇸 · Rabindra N. Mohapatra🇺🇸 · Yongchao Zhang🇺🇸

    A light CP-even Standard Model (SM) gauge-singlet scalar $S$ can be produced abundantly in the supernova core, via the nucleon bremsstrahlung process $NN\to NNS$, due to its mixing with the SM Higgs boson. Including the effective $S$ coupling to both nucleons and the pion mediators, we evaluate the production amplitude for the $S$ particle and point out a key difference with the well-known light CP-odd scalar (axion) and vector boson (dark photon) cases. Taking the subsequent decay and re-absorption of $S$ into account, we present a complete calculation of the energy loss rate for the $S$ particle. We then use the SN1987A luminosity constraints to derive updated supernova limits on the mixing of the scalar $S$ with the SM Higgs boson. We find that the mixing angle $\sin \theta$ with the SM Higgs is excluded only in the narrow range of $3.9\times 10^{-7}$ to $7.0\times 10^{-6}$, depending on the scalar mass up to about 147 MeV, beyond which the supernova limit disappears.

    hep-phastro-ph.COastro-ph.HEastro-ph.SRJCAP(2020)·79 citations
13. 13*

    Electroweak-Symmetric Dark Monopoles from Preheating

    Yang Bai🇺🇸 · Mrunal Korwar🇺🇸 · Nicholas Orlofsky🇺🇸

    If the dark sector contains 't Hooft-Polyakov monopoles and a small enough dark gauge coupling, dark monopoles could be a macroscopic dark matter candidate. Its Higgs-portal coupling to the Standard Model can modify the electroweak vacuum in the monopole interior. In the most striking cases, dark monopoles could even contain electroweak-symmetric cores and generate multi-hit signals at large-volume detectors. If they are produced via parametric resonance in the early Universe, monopoles with radii up to one micron and masses up to ten kilotonnes could account for all of dark matter.

    hep-phastro-ph.COJHEP(2020)·28 citations
14. 14*

    The hadronic coupling constants of the lowest hidden-charm pentaquark state with the QCD sum rules in rigorous quark-hadron duality

    Zhi-Gang Wang🇨🇳 · Hui-Juan Wang🇨🇳 · Qi Xin🇨🇳

    In this article, we illustrate how to calculate the hadronic coupling constants of the pentaquark states with the QCD sum rules based on rigorous quark-hadron quality, then study the hadronic coupling constants of the lowest diquark-diquark-antiquark type hidden-charm pentaquark state with the spin-parity $J^P={\frac{1}{2}}^{-}$ in details, and calculate the partial decay widths. The total width $\Gamma (P_c)=14.32\pm 3.31\mathrm{MeV}$ is compatible with the experimental value ${\Gamma }_{P_c(4312)}=9.8\pm 2.7_{-4.5}^{+3.7}\text{mbox}MeV$ from the LHCb collaboration, and favors assigning the $P_c(4312)$ to be the $[ud][uc]\bar{c}$ pentaquark state with the $J^P={\frac{1}{2}}^{-}$. The hadronic coupling constants have the relation $|G_{P{D}^{-}{\Sigma }_c^{++}}|=\sqrt{2}|G_{P{\bar{D}}^0{\Sigma }_c^{+}}|\gg |G_{P{\bar{D}}^0{\Lambda }_c^{+}}|$, and favor the hadronic dressing mechanism. The $P_c(4312)$ maybe have a diquark-diquark-antiquark type pentaquark core with the typical size of the $qqq$-type baryon states, the strong couplings to the meson-baryon pairs $\bar{D}{\Sigma }_c$ lead to some pentaquark molecule components, and the $P_c(4312)$ maybe spend a rather large time as the $\bar{D}{\Sigma }_c$ molecular state.

    hep-phCPC(2021)·27 citations
15. 15*

    The Lifshitz Regime and its Experimental Signals

    R. D. Pisarski🇺🇸 · F. Rennecke🇺🇸 · A. Tsvelik🇺🇸 · S. Valgushev🇺🇸

    We discuss the possibility of a Lifshitz regime, where the dispersion relation for Goldstone bosons and related fields has a minimum at nonzero momenta. Studies with the Functional Renormalization Group suggest that this occurs over a wide region in the plane of temperature and baryon chemical potential. Conversely, the FRG finds that the region in which fluctuations from a critical endpoint are significant is rather small. We suggest that this is due generically to the narrowness of the tricritical region in the chiral limit. Even if particles are produced in thermal equilibrium, a dispersion relation which is non-monotonic in momenta produces what appears to be non-thermal behavior.

    ↳ nucl-thhep-phNPA(2021)·25 citations
16. 16*

    Light nuclei production in relativistic heavy ion collisions from the AMPT model

    Kai-Jia Sun🇺🇸 · Che Ming Ko🇺🇸

    Based on an improved multiphase transport (AMPT) model, which gives a good description of proton production with a smooth quark matter to hadronic matter transition in relativistic heavy ion collisions, we study deuteron and triton production from the coalescence of nucleons at the kinetic freezeout of these collisions. For Au+Au collisions at center-of-mass energies $\sqrt{s_{\text{NN}}}$ from 7.7 GeV to 200 GeV available at the Relativistic Heavy Ion Collider (RHIC), we find that the yield ratio $N_{\text{t}}{N}_{\text{p}}/N_{\text{d}}^2$ of proton, deuteron\com{,} and triton is essentially a constant as a function of collision energy. Our result confirms the expectation that without a first-order quark to hadronic matter phase transition in the produced matter or its approach to the critical point of the QCD matter, this yield ratio does not show any non-monotonic behavior in its collision energy dependence.

    ↳ nucl-thhep-phPRC(2021)·46 citations
17. 17*

    Self-absorption of synchrotron radiation in a laser-irradiated plasma

    T. G. Blackburn🇸🇪 · A. J. MacLeod🇬🇧 · A. Ilderton🇬🇧 · B. King🇬🇧 · S. Tang🇬🇧 · M. Marklund🇸🇪

    Electrons at the surface of a plasma that is irradiated by a laser with intensity in excess of $10^{23}\mathrm{W}{\mathrm{cm}}^{-2}$ are accelerated so strongly that they emit bursts of synchrotron radiation. Although the combination of high photon and electron density and electromagnetic field strength at the plasma surface makes particle-particle interactions possible, these interactions are usually neglected in simulations of the high-intensity regime. Here we demonstrate an implementation of two such processes: photon absorption and stimulated emission. We show that, for plasmas that are opaque to the laser light, photon absorption would cause complete depletion of the multi-keV region of the synchrotron photon spectrum, unless compensated by stimulated emission. Our results motivate further study of the density dependence of QED phenomena in strong electromagnetic fields.

    ↳ physics.plasm-phhep-phPhys.Plasmas(2021)·4 citations
18. 18*

    Gravitational production of nearly thermal fermionic Dark Matter

    Nathan Herring🇺🇸 · Daniel Boyanovsky🇺🇸

    We consider the cosmological production of fermionic dark matter during inflation and a post-inflationary radiation dominated era. This fermion \emph{only interacts gravitationally}, has a mass $m$ much smaller than the Hubble scale during inflation (but is otherwise arbitrary) and is in its Bunch-Davies vacuum state during inflation. We focus on superhorizon modes at the end of inflation, and assume instantaneous reheating. We obtain the full energy momentum tensor discussing its renormalization, and show that the contribution from particle production is of the kinetic-fluid form near matter-radiation equality. We find \emph{exactly} the distribution function of produced particles $|B(k){|}^2=\frac{1}{2}[1-(1-e^{-\frac{k^2}{2m{T}_H}}{)}^{1/2}]$ which exhibits an " emergent temperature" $T_H=H_0\sqrt{{\Omega }_R}\simeq 10^{-36}(\mathrm{eV})$. The abundance of the produced particles ${\Omega }_{pp}$ is very similar to that of a non-relativistic degree of freedom thermalized at temperature $T_H$, ${\Omega }_{pp}\propto m(m{T}_H{)}^{3/2}\simeq (m/10^8\mathrm{GeV}){)}^{5/2}$ and "cold" equation of state $w(a)\simeq (T_H/m{a}^2)$, both dominated by superhorizon modes at the end of inflation. We discuss subtle aspects of isocurvature perturbations.

    ↳ astro-ph.COgr-qchep-phhep-thPRD(2020)·36 citations
19. 19*

    Time-Scales for Nonlinear Processes in Preheating after Multifield Inflation with Nonminimal Couplings

    Jorinde van de Vis · Rachel Nguyen · Evangelos I. Sfakianakis · John T. Giblin · Jr. · David I. Kaiser

    We have conducted extensive lattice simulations to study the post-inflation dynamics of multifield models involving nonminimal couplings. We explore the parameter dependence of preheating in these models and describe the various time-scales that control such nonlinear processes as energy transfer, re-scattering, and the approach to radiation-domination and thermalization. In the limit of large nonminimal couplings (${\xi }_I\sim 100$), we find that efficient transfer of energy from the inflaton condensate to radiative degrees of freedom, emergence of a radiation-dominated equation of state, and the onset of thermalization each consistently occur within $N_{\mathrm{reh}}\lesssim 3$ $e$-folds after the end of inflation, largely independent of the values of the other couplings in the models. The exception is the case of negative ellipticity, in which there is a misalignment between the dominant direction in field-space along which the system evolves and the larger of the nonminimal couplings ${\xi }_I$. In those cases, the field-space-driven parametric resonance is effectively shut off. More generally, the competition between the scalar fields' potential and the field-space manifold structure can yield interesting phenomena such as two-stage resonances. Despite the explosive particle production, which can lead to a quick depletion of the background energy density, the nonlinear processes do not induce any super-horizon correlations after the end of inflation in these models, which keeps predictions for CMB observables unaffected by the late-time amplification of isocurvature fluctuations. Hence the excellent agreement between primordial observables and recent observations is preserved for this class of models, even when we consider post-inflation dynamics.

    ↳ astro-ph.COhep-phhep-thPRD(2020)·50 citations
20. 20*

    Weak charge and weak radius of ${}^{12}$C

    Oleksandr Koshchii🇩🇪 · Jens Erler🇩🇪 · Mikhail Gorchtein🇩🇪 · Charles J. Horowitz🇺🇸 · Jorge Piekarewicz🇺🇸 · Xavier Roca-Maza🇮🇹 · Chien-Yeah Seng🇩🇪 · Hubert Spiesberger🇩🇪

    We present a feasibility study of a simultaneous sub-percent extraction of the weak charge and the weak radius of the ${}^{12}$C nucleus using parity-violating electron scattering, based on a largely model-independent assessment of the uncertainties. The corresponding measurement is considered to be carried out at the future MESA facility in Mainz with $E_{\mathrm{beam}}=155$ MeV. We find that a combination of a $0.3\%$ precise measurement of the parity-violating asymmetry at forward angles with a $10\%$ measurement at backward angles will allow to determine the weak charge and the weak radius of ${}^{12}$C with $0.4\%$ and $0.5\%$ precision, respectively. These values could be improved to $0.3\%$ and $0.2\%$ for a $3\%$ backward measurement. This experimental program will have impact on precision low-energy tests in the electroweak sector and nuclear structure.

    ↳ nucl-thhep-phnucl-exPRC(2020)·14 citations
21. 21*

    Magnetic catalysis and the chiral condensate in holographic QCD

    Alfonso Ballon-Bayona🇧🇷 · Jonathan P. Shock🇿🇦 · Dimitrios Zoakos🇬🇷

    We investigate the effect of a non-zero magnetic field on the chiral condensate using a holographic QCD approach. We extend the model proposed by Iatrakis, Kiritsis and Paredes in arXiv:1010.1364 that realises chiral symmetry breaking dynamically from 5d tachyon condensation. We calculate the chiral condensate, magnetisation and susceptibilities for the confined and deconfined phases. The model leads, in the probe approximation, to magnetic catalysis of chiral symmetry breaking in both confined and deconfined phases. In the chiral limit, $m_q=0$, we find that in the deconfined phase a sufficiently strong magnetic field leads to a second order phase transition from the chirally restored phase to a chirally broken phase. The transition becomes a crossover as the quark mass increases. Due to a scaling in the temperature, the chiral transition will also be interpreted as a transition in the temperature for fixed magnetic field. We elaborate on the relationship between the chiral condensate, magnetisation and the (magnetic) free energy density. We compare our results at low and moderate temperatures temperatures with lattice QCD results.

    ↳ hep-thhep-lathep-phJHEP(2020)·30 citations
22. 22*

    Multi-field inflation and preheating in asymmetric $\alpha$-attractors

    Oksana Iarygina🇳🇱 · Evangelos I. Sfakianakis🇳🇱 · Dong-Gang Wang🇳🇱 · Ana Achúcarro🇳🇱

    We analyze and compare the multi-field dynamics during inflation and preheating in symmetric and asymmetric models of $\alpha$-attractors, characterized by a hyperbolic field-space manifold. We show that the generalized (asymmetric) E- and (symmetric) T-models exhibit identical two-field dynamics during inflation for a wide range of initial conditions. The resulting motion can be decomposed in two approximately single-field segments connected by a sharp turn in field-space. The details of preheating can nevertheless be different. For the T-model one main mass-scale dominates the evolution of fluctuations of the spectator field, whereas for the E-model, a competing mass-scale emerges due to the steepness of the potential away from the inflationary plateau, leading to different contributions to parametric resonance for small and large wave-numbers. Our linear multi-field analysis of fluctuations indicates that for highly curved manifolds, both the E- and T-models preheat almost instantaneously. For massless fields this is always due to efficient tachyonic amplification of the spectator field, making single-field results inaccurate. Interestingly, there is a parameter window corresponding to $r=\mathcal{O}(10^{-5})$ and massive fields, where the preheating behavior is qualitatively and quantitatively different for symmetric and asymmetric potentials. In that case, the E-model can completely preheat due to self-resonance for values of the curvature where preheating in the T-model is inefficient. This provides a first distinguishing feature between models that otherwise behave identically, both at the single-field and multi-field level. Finally, we discuss how one can describe multi-field preheating on a hyperbolic manifold by identifying the relevant mass-scales that control the growth of inflaton and spectator fluctuations, which can be applied to any $\alpha$-attractor model and beyond.

    ↳ astro-ph.COgr-qchep-phhep-th46 citations
23. 23*

    Improved isotope-shift-based bounds on bosons beyond the Standard Model through measurements of the ${}^2$D${}_{3/2}{-}^2$D${}_{5/2}$ interval in Ca${}^{+}$

    Cyrille Solaro🇩🇰 · Steffen Meyer🇩🇰 · Karin Fisher🇩🇰 · Julian C. Berengut🇦🇺 · Elina Fuchs🇺🇸 · Michael Drewsen🇩🇰

    We perform high-resolution spectroscopy of the $3$d${}^2$D${}_{3/2}-3$d${}^2$D${}_{5/2}$ interval in all stable even isotopes of ${}^A$Ca${}^{+}$ (A = 40, 42, 44, 46 and 48) with an accuracy of $\sim$ 20 Hz using direct frequency-comb Raman spectroscopy. Combining these data with isotope shift measurements of the 4s${}^2$S${}_{1/2}\leftrightarrow 3$d${}^2$D${}_{5/2}$ transition, we carry out a King plot analysis with unprecedented sensitivity to coupling between electrons and neutrons by bosons beyond the Standard Model. Furthermore, we estimate the sensitivity to such bosons from equivalent spectroscopy in Ba${}^{+}$ and Yb${}^{+}$. Finally, the data yield isotope shifts of the 4s${}^2$S${}_{1/2}\leftrightarrow 3$d${}^2$D${}_{3/2}$ transition at 10 part-per-billion through combination with recent data of Knollmann et al (2019).

    ↳ physics.atom-phhep-exhep-phquant-phPRL(2020)·74 citations
24. 24*

    Two-Loop Corrections to the Large-Order Behavior of Correlation Functions in the One-Dimensional N-Vector Model

    L. T. Giorgini🇸🇪 · U. D. Jentschura🇺🇸 · E. M. Malatesta · G. Parisi🇮🇹 · T. Rizzo🇺🇸 · J. Zinn-Justin🇫🇷

    For a long time, the predictive limits of perturbative quantum field theory have been limited by our inability to carry out loop calculations to arbitrarily high order, which become increasingly complex as the order of perturbation theory is increased. This problem is exacerbated by the fact that perturbation series derived from loop diagram (Feynman diagram) calculations represent asymptotic (divergent) series which limits the predictive power of perturbative quantum field theory. Here, we discuss an ansatz which could overcome these limits, based on the observations that (i) for many phenomenologically relevant field theories, one can derive dispersion relations which relate the large-order growth (the asymptotic limit of "infinite loop order") with the imaginary part of arbitrary correlation functions, for negative coupling ("unstable vacuum"), and (ii) one can analyze the imaginary part for negative coupling in terms of classical field configurations (instantons). Unfortunately, the perturbation theory around instantons, which could lead to much more accurate predictions for the large-order behavior of Feynman diagrams, poses a number of technical as well as computational difficulties. Here, we study, to further the above mentioned ansatz, correlation functions in a one-dimensional (1D) field theory with a quartic self-interaction and an O(N) internal symmetry group, otherwise known as the 1D N-vector model. Our focus is on corrections to the large-order growth of perturbative coefficients, i.e., the limit of a large number of loops in the Feynman diagram expansion. We evaluate, in momentum space, the two-loop corrections for the two-point correlation function, and its derivative with respect to the momentum, as well as the two-point correlation function with a wigglet insertion. Also, we study the four-point function.

    ↳ hep-thhep-phPRD(2020)·4 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.