1,720,982 research outputs found
Dark gauge boson emission from supernova pions
No full textThe hot, neutron-rich, and dense circumstance in core-collapse supernovae provides a source of negatively charged pions that may make up a significant portion of the matter. These abundant thermal pions offer an opportunity to populate light and hidden hypothetical particles. In this study, we discuss the dark gauge boson production via reactions involving supernova pions. The rate of this production is determined by the isovector nucleon coupling. We consider two toy models, the dark photon and the gauged B-L models, that carry the typical distinct isovector nucleon coupling structure in the medium. Pion-induced dark gauge bosons leave an imprint on several observational consequences associated with supernova. Their sizable emissivity and characteristic hard spectral distribution result in the stringent constraints on the dark gauge boson models, in particular at masses above the two electron mass. © 2023 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the https://creativecommons.org/licenses/by/4.0/Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.11Nsciescopu
Magnetogenesis from a rotating scalar: à la scalar chiral magnetic effect
No full text© 2020, The Author(s). The chiral magnetic effect (CME) is a phenomenon in which an electric current is induced parallel to an external magnetic field in the presence of chiral asymmetry in a fermionic system. In this paper, we show that the electric current induced by the dynamics of a pseudo-scalar field which anomalously couples to electromagnetic fields can be interpreted as closely analogous to the CME. In particular, the velocity of the pseudo-scalar field, which is the phase of a complex scalar, indicates that the system carries a global U(1) number asymmetry as the source of the induced current. We demonstrate that an initial kick to the phase-field velocity and an anomalous coupling between the phase-field and gauge fields are naturally provided, in a set-up such as the Affleck-Dine mechanism. The resulting asymmetry carried by the Affleck-Dine field can give rise to instability in the (electro)magnetic field. Cosmological consequences of this mechanism are also investigated11Nsciescopu
Clockwork inflation with non-minimal coupling
No full text© 2019, The Author(s).We suggest a clockwork mechanism for a Higgs-like inflation with the non-minimal coupling term ξϕ2R. The seemingly unnatural ratio of parameters, λ/ ξ2∼ 10 - 10 of the self quartic coupling of the inflaton, λ, and the non-minimal coupling, ξ, is understood by exponential suppression of λ by the clockwork mechanism, instead of a large non-minimal coupling. The portal interaction between the inflaton and the Standard Model (SM) Higgs doublet is introduced as a source of reheating and the inflaton mass. Successful realization of inflation requires that the inflaton gets a mass around (sub) GeV scale, which would lead to observable consequences depending on reheating process and its lifetime11Nsciescopu
Axion scales and couplings with Stückelberg mixing
No full text© 2019, The Author(s).We study the axion field range and low energy couplings in models with Stückelberg mixing between axions and U(1) gauge bosons. It is noted that the gauge- invariant axion combination ξ in the model is periodic modulo an appropriate shift of gauge-variant axions eaten by the massive U(1) gauge bosons, which in some cases makes the connection between the field range and the low energy couplings less transparent. We derive the field range of ξ for generic forms of the axion kinetic metric and U(1) charges, and identify the field basis for which all non-derivative couplings of ξ are quantized in a manner manifestly consistent with the periodicity of ξ. Generically Stückelberg mixing reduces the axion field range. In particular, the mixings between N axions and (N − 1) U(1) gauge bosons typically result in an exponentially reduced field range Mξ=O(k−(N−1)f/N!) for the residual gauge-invariant axion ξ in the limit N ≫ 1, where f and k denote the typical decay constant and the root mean square of the U(1) gauge charges of the original N axions. Using simple examples, we study also the reparameterization-invariant physical quantities such as the axion effective potential and 1PI couplings to gauge bosons, which are determined by the reparameterization-dependent axion couplings in the model11Nsciescopu
Aligned natural inflation in the Large Volume Scenario
No full text© 2021, The Author(s).We embed natural inflation in an explict string theory model and derive observables in cosmology. We achieve this by compactifying the type IIB string on a Calabi-Yau orientifold, stabilizing moduli via the Large Volume Scenario, and configuring axions using D7-brane stacks. In order to obtain a large effective decay constant, we employ the Kim-Nilles-Peloso alignment mechanism, with the required multiple axions arising naturally from generically anisotropic bulk geometries. The bulk volumes, and hence the axion decay constants, are stabilized by generalized one-loop corrections and subject to various conditions: the Kähler cone condition on the string geometry; the convex hull condition of the weak gravity conjecture; and the constraint from the power spectrum of scalar perturbations. We find that all constraints can be satisfied in a geometry with relatively small volume and thus heavy bulk axion mass. We also covariantize the convex hull condition for the axion-dilaton-instanton system and verify the normalization of the extremal bound.11Nsciescopu
Peccei-Quinn relaxion
No full textAbstract The relaxation mechanism, which solves the electroweak hierarchy problem without relying on TeV scale new physics, crucially depends on how a Higgs-dependent back-reaction potential is generated. In this paper, we suggest a new scenario in which the scalar potential induced by the QCD anomaly is responsible both for the relaxation mechanism and the Peccei-Quinn mechanism to solve the strong CP problem. The key idea is to introduce the relaxion and the QCD axion whose cosmic evolutions become quite different depending on an inflaton-dependent scalar potential. Our scheme raises the cutoff scale of the Higgs mass up to 107 GeV, and allows reheating temperature higher than the electroweak scale as would be required for viable cosmology. In addition, the QCD axion can account for the observed dark matter of the universe as produced by the conventional misalignment mechanism. We also consider the possibility that the couplings of the Standard Model depend on the inflaton and become stronger during inflation. In this case, the relaxation can be implemented with a sub-Planckian field excursion of the relaxion for a cutoff scale below 10 TeV
Massless preheating and electroweak vacuum metastability
No full textPublished by the American Physical SocietyCurrent measurements of Standard Model parameters suggest that the electroweak vacuum is metastable. This metastability has important cosmological implications, because large fluctuations in the Higgs field could trigger vacuum decay in the early Universe. For the false vacuum to survive, interactions which stabilize the Higgs during inflation—e.g., inflaton-Higgs interactions or nonminimal couplings to gravity—are typically necessary. However, the postinflationary preheating dynamics of these same interactions could also trigger vacuum decay, thereby recreating the problem we sought to avoid. This dynamics is often assumed catastrophic for models exhibiting scale invariance, since these generically allow for unimpeded growth of fluctuations. In this paper, we examine the dynamics of such “massless preheating” scenarios and show that the competing threats to metastability can nonetheless be balanced to ensure viability. We find that fully accounting for both the backreaction from particle production and the effects of perturbative decays reveals a large number of disjoint “islands of (meta)stability” over the parameter space of couplings. Ultimately, the interplay among Higgs-stabilizing interactions plays a significant role, leading to a sequence of dynamical phases that effectively extend the metastable regions to large Higgs-curvature couplings.11Nsciescopu
Exploring the Universe with dark light scalars
No full textWe study the cosmology of the dark sector consisting of (ultra)light scalars. Since the scalar mass is radiatively unstable, a special explanation is required to make the mass much smaller than the UV scale. There are two well-known mechanisms for the origin of scalar mass. The scalar can be identified as a pseudo-Goldstone boson, whose shift symmetry is explicitly broken by nonperturbative corrections, like the axion. Alternatively, it can be identified as a composite particle like the glueball, whose mass is limited by the confinement scale of the theory because no scalar degree of freedom exists at high scales. In both cases, the scalar can be naturally light, but interaction behavior is quite different. The lighter the axion (glueball), the weaker (stronger) its interaction. As the simplest nontrivial example, we consider the dark axion whose shift symmetry is anomalously broken by the hidden non-Abelian gauge symmetry. After the confinement of the gauge group, the dark axion and the dark glueball get masses and both form multicomponent dark matter. We carefully consider the effects of energy flow from the dark gluons to the dark axions and derive the full equations of motion for the background and the perturbed variables. The effect of the dark axion-dark gluon coupling on the evolution of the entropy and the isocurvature perturbations is also clarified. Finally, we discuss the gravothermal collapse of the glueball subcomponent dark matter after the halos form, in order to explore the potential to contribute to the formation of seeds for the supermassive black holes observed at high redshifts. With the simplified assumptions, the glueball subcomponent dark matter with the mass of 0.01-0.1 MeV and the axion main dark matter component with the decay constant f(a) = O(10(15)-10(16)) GeV and the mass of O(10(-14)-10(-18)) eV can provide a hint on the origin of the supermassive black holes at high redshifts.11Nsciescopu
The dS swampland conjecture with the electroweak symmetry and QCD chiral symmetry breaking
No full textAbstract The dS swampland conjecture |∇V|/V ≥ c, where c is presumed to be a positive constant of order unity, implies that the dark energy density of our Universe can not be a cosmological constant, but mostly the potential energy of an evolving quintessence scalar field. As the dark energy includes the effects of the electroweak symmetry breaking and the QCD chiral symmetry breaking, if the dS swampland conjecture is applicable for the low energy quintessence potential, it can be applied for the Higgs and pion potential also. On the other hand, the Higgs and pion potential has the well-known dS extrema, and applying the dS swampland conjecture to those dS extrema may provide stringent constraints on the viable quintessence, as well as on the conjecture itself. We examine this issue and find that the pion dS extremum at cos(π 0/f π ) = −1 implies c ≲ O (10−2–10−5) for arbitrary form of the quintessence potential and couplings, where the weaker bound (10−2) is available only for a specific type of quintessence whose couplings respect the equivalence principle, while the stronger bound (10−5) applies for generic quintessence violating the equivalence principle. We also discuss the possibility to relax this bound with an additional scalar field, e.g. a light modulus which has a runaway behavior at the pion dS extremum. We argue that such possibility is severely constrained by a variety of observational constraints which do not leave a room to significantly relax the bound. We make a similar analysis for the Higgs dS extremum at H = 0, which results in a weaker bound on c
Cooling of young neutron stars and dark gauge bosons
No full textThe standard cooling scenario in the presence of nucleon superfluidity fits rather well to the observation of the neutron stars. It implies that the stellar cooling arguments could place a stringent constraint on the properties of novel particles. We study in particular the cooling rate induced by dark gauge bosons for very young neutron stars: remnants of Cassiopeia A and SN1987A. The cooling is dominantly contributed either by the nucleon pair breaking and formation in the core or by the electron bremsstrahlung in the crust, depending on the age of the stars and the form of the couplings. We compute how much the cooling curve of the young neutron stars could be modified by the extra dark gauge boson emission and obtain the bound for the dark gauge boson when its mass is lower than O(0.1) MeV; for the dark photon, we find the mixing parameter times its mass µmγ′<1.5×10-8 MeV and for the U(1)B-L gauge boson its coupling to nucleons and electrons e′<5×10-13. We also discuss the possibility that the rapid cooling of Cas A might provide a hint for the existence of the U(1)B-L gauge boson of mass around eV and its coupling e′∼10-13.11Nsciescopu
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