scholarly journals An even lighter QCD axion

2021 ◽  
Vol 2021 (5) ◽  
Author(s):  
Luca Di Luzio ◽  
Belen Gavela ◽  
Pablo Quilez ◽  
Andreas Ringwald
Keyword(s):  
Neutron Star ◽  
Analytical Formula ◽  
Mass Region ◽  
Strong Impact ◽  
Axion Mass ◽  
Total Potential ◽  
Axion Field ◽  
Discovery Potential ◽  
Model Independent ◽  
Significant Model

Abstract We explore whether the axion which solves the strong CP problem can naturally be much lighter than the canonical QCD axion. The $$ {Z}_{\mathcal{N}} $$ Z N symmetry proposed by Hook, with $$ \mathcal{N} $$ N mirror and degenerate worlds coexisting in Nature and linked by the axion field, is considered in terms of generic effective axion couplings. We show that the total potential is safely approximated by a single cosine in the large $$ \mathcal{N} $$ N limit, and we determine the analytical formula for the exponentially suppressed axion mass. The resulting universal enhancement of all axion interactions relative to those of the canonical QCD axion has a strong impact on the prospects of axion-like particle experiments such as ALPS II, IAXO and many others: experiments searching for generic axion-like particles have in fact discovery potential to solve the strong CP problem. The finite density axion potential is also analyzed and we show that the $$ {Z}_{\mathcal{N}} $$ Z N asymmetric background of high-density stellar environments sets already significant model-independent constraints: 3 ≤ $$ \mathcal{N} $$ N ≲ 47 for an axion scale fa ≲ 2.4 × 1015 GeV, with tantalizing discovery prospects for any value of fa and down to $$ \mathcal{N} $$ N ∼ 9 with future neutron star and gravitational wave data, down to the ultra-light mass region. In addition, two specific ultraviolet $$ {Z}_{\mathcal{N}} $$ Z N completions are developed: a composite axion one and a KSVZ-like model with improved Peccei-Quinn quality.

WHY IS THE HIDDEN SECTOR INVISIBLE?

2000 ◽  
Vol 15 (35) ◽  
pp. 2131-2137 ◽  
Author(s):  
M. D. POLLOCK
Keyword(s):  
Degrees Of Freedom ◽  
Coupling Parameter ◽  
Vacuum State ◽  
Fine Tuning ◽  
Gauge Mediation ◽  
Superstring Theory ◽  
Thermodynamical Equilibrium ◽  
Hidden Sector ◽  
Axion Field ◽  
Model Independent

The hidden sector of the E8×E′8 heterotic superstring theory of Gross et al. can in principle contain additional "shadow" matter, interacting only gravitationally with the real world in which we live. The SU (3)′ C × SU (2)′ L × U (1)′ Y shadow configuration symmetric to the standard model has been ruled out by Kolb et al. from nucleosynthesis arguments, combined with the existence of three light neutrinos. In the absence of inflation and of entropy enhancement by the out-of-equilibrium decay of an unstable particle, the same exclusion applies to the unbroken E′8 hidden gauge group, assuming thermodynamical equilibrium with the observable sector E6 group, and consequently all breaking chains E′8→ G1×G2×⋯, since they can only reduce the effective number of four-dimensional degrees of freedom g eff . The hidden sector would then appear to be in its vacuum state, which implies the absence of all condensates as well, if their potentials are positive semi-definite. In this case, and if there is no anomalous U(1) symmetry in the observable sector, the QCD axion is the model-independent axion, whose decay constant [Formula: see text] (where [Formula: see text] is the strong-interaction coupling parameter) requires a fine-tuning of the initial value of this axion field to ai/fa≲3×10-3, in order not to overclose the Universe today, supersymmetry being broken by gauge mediation. Vice versa, if ai/fa~1, then hidden-sector gaugino condensation is necessary for there to be a sufficiently massive gravitino, whose decay can increase the entropy. Astronomical microlensing observations may help to discriminate between these two cases.

scholarly journals Production and decay of radion in Randall–Sundrum model at a photon collider

2014 ◽  
Vol 29 (27) ◽  
pp. 1450136 ◽  
Author(s):  
Gi-Chol Cho ◽  
Yoshiko Ohno
Keyword(s):  
Scalar Particle ◽  
Mass Region ◽  
Momentum Tensor ◽  
Beyond The Standard Model ◽  
Higgs Search ◽  
The Standard Model ◽  
Discovery Potential ◽  
Photon Collider ◽  
Warped Extra Dimension ◽  
Low Mass

A warped extra dimension model predicts an extra scalar particle beyond the Standard Model (SM) which is called a radion. Although interactions of the radion are similar to those of the Higgs boson in the SM, a relatively light radion (≲100 GeV) is not severely constrained from the Higgs search experiments at the LHC. In this paper we study discovery potential of the radion at a photon collider as an option of ILC. Owing to the trace anomaly of the energy–momentum tensor, both a production of radion in γγ collision and its decay to gluon pair are enhanced sizably. We find that the photon collider has a sensitivity for discovering the radion in low-mass region up to Λϕ~3 TeV, where Λϕ is a scale parameter which suppresses the interactions of radion to the SM particles.

scholarly journals Numerically fitting the electron Fermi energy and the electron fraction in a neutron star

2016 ◽  
Vol 25 (01) ◽  
pp. 1650002 ◽  
Author(s):  
Xing Hu Li ◽  
Zhi Fu Gao ◽  
Xiang Dong Li ◽  
Yan Xu ◽  
Pei Wang ◽  
...  
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Fermi Energy ◽  
Thermal Evolution ◽  
Mean Field ◽  
Analytical Formula ◽  
Matter Density ◽  
Relativistic Electrons ◽  
Future Studies ◽  
Energy Formula

Based on the basic definition of the Fermi energy of degenerate and relativistic electrons, we obtain a special solution to the electron Fermi energy, [Formula: see text], and express [Formula: see text] as a function of the electron fraction, [Formula: see text], and matter density, [Formula: see text]. We obtain several useful analytical formula for [Formula: see text] and [Formula: see text] within classical models and the work of Dutra et al. (2014) (Type-2) in relativistic mean-field theory are obtained using numerically fitting. When describing the mean-field Lagrangian, density, we adopt the TMA parameter set, which is remarkably consistent with the updated astrophysical observations of neutron stars (NSs). Due to the importance of the density dependence of the symmetry energy, [Formula: see text], in nuclear astrophysics, a brief discussion on [Formula: see text] and its slop is presented. Combining these fitting formula with boundary conditions for different density regions, we can evaluate the value of [Formula: see text] in any given matter density, and obtain a schematic diagram of [Formula: see text] as a continuous function of [Formula: see text]. Compared with previous studies on the electron Fermi energy in other studies models, our methods of calculating [Formula: see text] are more simple and convenient, and can be universally suitable for the relativistic electron regions in the circumstances of common neutron stars. We have deduced a general expression of [Formula: see text] and [Formula: see text], which could be used to indirectly test whether one equation of state of a NS is correct in our future studies on neutron star matter properties. Since URCA reactions are expected in the center of a massive star due to high-value electron Fermi energy and electron fraction, this study could be useful in the future studies on the NS thermal evolution.

scholarly journals Dirac-mode analysis for quark number density and its application for deconfinement transition

2018 ◽  
Vol 175 ◽  
pp. 12003
Author(s):  
Takahiro M. Doi ◽  
Kouji Kashiwa
Keyword(s):  
Lattice Qcd ◽  
Quark Mass ◽  
Chemical Potential ◽  
Analytical Formula ◽  
Mass Region ◽  
Polyakov Loop ◽  
Mode Analysis ◽  
Number Density ◽  
Mode Expansion ◽  
Quark Number

The quark number density at finite imaginary chemical potential is investigated in the lattice QCD using the Dirac-mode expansion. We find the analytical formula of the quark number density in terms of the Polyakov loop in the large quark mass regime. On the other hand, in the small quark mass region, the quark number density is investigated by using the quenched lattice QCD simulation. The quark number density is found to strongly depend on the low-lying Dirac modes while its sign does not change. This result leads to that the quark number holonomy is not sensitive to the low-lying Dirac modes. We discuss the confinement-deconfinement transition from the property of the quark number density and the quark number holonomy.

scholarly journals Model-independent inference of neutron star radii from moment of inertia measurements

2016 ◽  
Vol 93 (3) ◽  
Author(s):  
Carolyn A. Raithel ◽  
Feryal Özel ◽  
Dimitrios Psaltis
Keyword(s):  
Neutron Star ◽  
Moment Of Inertia ◽  
Model Independent

scholarly journals MIRROR WORLD AND AXION: RELAXING COSMOLOGICAL BOUNDS

2005 ◽  
Vol 20 (11) ◽  
pp. 2454-2458 ◽  
Author(s):  
MAURIZIO GIANNOTTI
Keyword(s):  
Mass Density ◽  
Temperature Dependent ◽  
Axion Mass ◽  
Upper Limit ◽  
Axion Field ◽  
Dependent Mass

The cosmological (upper) limit on the Peccei-Quinn constant, related to the primordial oscillations of the axion field, can be relaxed for a mirror axion model. The simple reason is that the mirror world is colder and so the behavior of the axion temperature-dependent mass is dominated by the contribution from the mirror sector. So the coherent oscillations start earlier and correspondingly the axion mass density Ωah2 is reduced.

scholarly journals Z lepton flavour violation as a probe for new physics at future $$e^+e^-$$ colliders

2021 ◽  
Vol 81 (12) ◽  
Author(s):  
Lorenzo Calibbi ◽  
Xabier Marcano ◽  
Joydeep Roy
Keyword(s):  
Field Theory ◽  
Effective Field Theory ◽  
New Physics ◽  
Effective Field ◽  
Low Energy ◽  
The Standard Model ◽  
Discovery Potential ◽  
Flavour Violation ◽  
Model Independent ◽  
Lepton Flavour

AbstractIn this work we assess the potential of discovering new physics by searching for lepton-flavour-violating (LFV) decays of the Z boson, $$Z\rightarrow \ell _i \ell _j$$ Z → ℓ i ℓ j , at the proposed circular $$e^+e^-$$ e + e - colliders CEPC and FCC-ee. Both projects plan to run at the Z-pole as a “Tera Z factory”, i.e., collecting $${\mathcal {O}}\left( 10^{12} \right) $$ O 10 12 Z decays. In order to discuss the discovery potential in a model-independent way, we revisit the LFV Z decays in the context of the Standard Model effective field theory and study the indirect constraints from LFV $$\mu $$ μ and $$\tau $$ τ decays on the operators that can induce $$Z\rightarrow \ell _i \ell _j$$ Z → ℓ i ℓ j . We find that, while the $$Z\rightarrow \mu e$$ Z → μ e rates are beyond the expected sensitivities, a Tera Z factory is promising for $$Z\rightarrow \tau \ell $$ Z → τ ℓ decays, probing New Physics at the same level of future low-energy LFV observables.

scholarly journals Neutron Star Properties: Quantifying the Effect of the Crust–Core Matching Procedure

Universe ◽  
2020 ◽  
Vol 6 (11) ◽  
pp. 220
Author(s):  
Márcio Ferreira ◽  
Constança Providência
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Nuclear Matter ◽  
Strong Impact ◽  
The Core ◽  
Meta Modeling ◽  
Low Mass ◽  
Matching Procedure ◽  
The Impact

The impact of the equation of state (EoS) crust-core matching procedure on neutron star (NS) properties is analyzed within a meta-modeling approach. Using a Taylor expansion to parametrize the core equation of state (EoS) and the SLy4 crust EoS, we create two distinct EoS datasets employing two matching procedures. Each EoS describes cold NS matter in a β equilibrium that is thermodynamically stable and causal. It is shown that the crust-core matching procedure affects not only the crust-core transition but also the nuclear matter parameter space of the core EoS, and thus the most probable nuclear matter properties. An uncertainty of as much as 5% (8%) on the determination of low mass NS radii (tidal deformability) is attributed to the complete matching procedure, including the effect on core EoS. By restricting the analysis, imposing that the same set of core EoS is retained in both matching procedures, the uncertainty on the NS radius drops to 3.5% and below 1.5% for 1.9M⊙. Moreover, under these conditions, the crust-core matching procedure has a strong impact on the Love number k2, of almost 20% for 1.0M⊙ stars and 7% for 1.9M⊙ stars, but it shows a very small impact on the tidal deformability Λ, below 1%.

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