arXiv subjects

S. -H. Henry Tye

Publications and source records attributed to S. -H. Henry Tye.

At least 19 recordsLinked to original sources

arXiv2026

Production of Primordial Black Holes in the Double D3-Brane - anti-D3-Brane Inflation Model

A natural extension of the successful $D3$-${\bar D}3$-brane inflation model in string theory is one with two $D3$-${\bar D}3$-brane pairs, giving rise to a novel feature in string-theory. When the first pair annihilates, $D1$-strings and $F1$-strings are produced. Following the non-commutative geometric properties in string theory, it is shown by Myers that the presence of the $D3$-charge field strength of the remaining $D3$-${\bar D}3$-brane pair leads to the formation of dielectric $3$-branes -- neutral, finite-size bound states of $3$-branes with $D1$-strings. They behave as matter with little or no pressure. Spanning a wide range of masses, they seed primordial black holes in the early universe.

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arXiv2025

The Lifespan of our Universe

The Dark Energy Survey (DES) and the Dark Energy Spectroscopic Instrument (DESI) measurements claim that the dark energy equation of state $w \ne -1$. This observation can be explained by the axion Dark Energy (aDE) model of an ultralight axion plus a cosmological constant $Λ$. Despite a relatively large degeneracy, there is a high probability that $Λ<0$. This negative $Λ$ leads the universe to end in a big crunch. Using the best-fit values of the model as a benchmark, we find the lifespan of our universe to be 33 billion years.

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arXiv2025

Dynamical dark energy from an ultralight axion

Recently the Dark Energy Survey (DES) Collaboration presented evidence that the equation of state $w$ of the dark energy is varying, or $w \simeq -0.948$ if it is constant. In either case, the dark energy cannot be due to a cosmological constant alone. Here we study an ultralight axion (or axion-like particle) with mass $m_ϕ\simeq 2 \times 10^{-33}$ eV that has properties that can explain the new $w$ measurement. In particular, $w\ge -1$ and a negative cosmological constant $Λ< 0$ is preferred in this model. We also present a simple formula for $w$ for the model to ease data fitting.

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arXiv2025

Diverse dark matter haloes in Two-field Fuzzy Dark Matter

Fuzzy dark matter (FDM) is a compelling candidate for dark matter, offering a natural explanation for the structure of diffuse low-mass haloes. However, the canonical FDM model with a mass of $10^{-22}~{\rm eV}$ encounters challenges in reproducing the observed diversity of dwarf galaxies, except for possibly scenarios where strong galactic feedback is invoked. The introduction of multiple-field FDM can provide a potential resolution to this diversity issue. The theoretical plausibility of this dark matter model is also enhanced by the fact that multiple axion species with logarithmically-distributed mass spectrum exist as a generic prediction of string theory. In this paper, we consider the axiverse hypothesis and investigate non-linear structure formation in the two-field fuzzy dark matter (2FDM) model. Our cosmological simulation with an unprecedented resolution and self-consistent initial conditions reveals the diverse structures of dark matter haloes in the 2FDM model for the first time. Depending on the formation time and local tidal activities, late-time haloes can host solitons of nested cores or solitons of one dominant species.

astro-ph.CO↗

arXiv2024

Nested solitons in two-field fuzzy dark matter

Dark matter as scalar particles consisting of multiple species is well motivated in string theory where axion fields are ubiquitous. A two-field fuzzy dark matter (FDM) model features two species of ultralight axion particles with different masses, $m_1 \neq m_2$, which is extended from the standard one-field model with $m_a \sim 10^{-22}\,{\rm eV}$. Here we perform numerical simulations to explore the properties of two-field FDM haloes. We find that the central soliton has a nested structure when $m_2 \gg m_1$, which is distinguishable from the generic flat-core soliton in one-field haloes. However, the formation of this nested soliton is subject to many factors, including the density fraction and mass ratio of the two fields. Finally, we study non-linear structure formation in two-field cosmological simulations with self-consistent initial conditions and find that the small-scale structure in two-field cosmology is also distinct from the one-field model in terms of DM halo counts and soliton formation time.

astro-ph.CO↗

arXiv2023

Baryon Number Violating Rate as A Function of the Proton-Proton Collision Energy

The baryon-number violation (BV) happens in the standard electroweak model. According to the Bloch-wave picture, the BV event rate shall be significantly enhanced when the proton-proton collision center of mass (COM) energy goes beyond the sphaleron barrier height $E_{\rm sph}\simeq 9.0\,{\rm TeV}$. Here we compare the BV event rates at different COM energies, using the Bloch-wave band structure and the CT18 parton distribution function data, with the phase space suppression factor included. As an example, the BV cross section at 25 TeV is 4 orders of magnitude bigger than its cross section at 13 TeV. The probability of detection is further enhanced at higher energies since an event at higher energy will produce on average more same sign charged leptons.

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arXiv2023

The Hubble Constant in the Axi-Higgs Universe

The $Λ$CDM model provides an excellent fit to the CMB data. However, a statistically significant tension emerges when its determination of the Hubble constant $H_0$ is compared to the local distance-redshift measurements. The axi-Higgs model, which couples an ultralight axion to the Higgs field, offers a specific variation of the $Λ$CDM model. It relaxes the $H_0$ tension as well as explains the $^7$Li puzzle in Big-Bang nucleosynthesis, the clustering $S_8$ tension with the weak-lensing data, and the observed isotropic cosmic birefringence in CMB. In this paper, we demonstrate how the $H_0$ and $S_8$ tensions can be relaxed simultaneously, by correlating the axion impacts on the early and late universe. In a benchmark scenario ($m=2 \times 10^{-30}$ eV) selected for experimental tests soon, the analysis combining the CMB+BAO+WL+SN data yields $H_0 = 69.9 \pm 1.5$ km/s/Mpc and $S_8 = 0.8045 \pm 0.0096$. Combining this (excluding the SN (supernovae) part) with the local distance-redshift measurements yields $H_0 = 72.42 \pm 0.76$ km/s/Mpc, while $S_8$ is slightly more suppressed.

astro-ph.CO↗

arXiv2023

A Novel Solution to the Gravitino Problem

In a general phenomenological model with local supersymmetry, the amount of massive gravitinos produced in early universe tends to violate the known dark matter density bound by many orders of magnitude. In the brane world scenario in Type IIB string theory, we propose a novel way to evade this problem. There, the standard model of strong and electroweak interactions live inside the anti-${\rm D3}$-branes ($\overline{\rm D3}$-branes) that span the 3 large spatial dimensions. Here, the "potential" Goldstino to be absorbed by the gravitino (to become massive) is the fermion component of the open string nilpotent superfield $X$ (i.e., $X^2=0$) which is present only inside the $\overline{\rm D3}$-branes. This non-linear supergravity scenario offers 2 ways to solve the gravitino problem, with very different particle physics phenomenologies.

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arXiv2021

Axi-Higgs Cosmology

If the electroweak Higgs vacuum expectation value $v$ in early universe is $\sim 1 \%$ higher than its present value $v_0=246$ GeV, the $^7$Li puzzle in BBN and the CMB/$Λ$CDM tension with late-universe measurements on Hubble parameter are mitigated. We propose a model of an axion coupled to the Higgs field, named ``axi-Higgs'', with its mass $m_a \sim 10^{-30} - 10^{-29}\,{\rm eV}$ and decay constant $f_a \sim 10^{17} - 10^{18}\,{\rm GeV}$, to achieve this goal. The axion initial value $a_{\rm ini}$ yields an initial $Δv_{\rm ini}/v_0 \sim 0.01$ throughout the BBN-recombination epoch and a percent level contribution to the total matter density today. Because of its very large de Broglie wavelength, this axion matter density $ω_a$ suppresses the matter power spectrum, alleviating the CMB/$Λ$CDM $S_8/σ_8$ tension with the weak-lensing data. It also explains the recently reported isotropic cosmic birefringence by its coupling with photons. Adding the axion ($m \sim 10^{-22}\,$eV) in the fuzzy dark matter model to the axi-Higgs model allows bigger $Δv_{\rm rec}$ and $ω_a$ to address the Hubble and $S_8/σ_8$ tensions simultaneously. The model predicts that $Δv$ may be detected by the spectral measurements of quasars, while its oscillation may be observed in the atomic clock measurements.

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arXiv2020

Standard Model from A Supergravity Model with a Naturally Small Cosmological Constant

Guided by the naturalness criterion for an exponentially small cosmological constant, we present a string theory motivated 4-dimensional $\mathcal{N}=1$ non-linear supergravity model (or its linear version with a nilpotent superfield) with spontaneous supersymmetry breaking. The model encompasses the minimal supersymmetric standard model, the racetrack Kähler uplift, and the KKLT anti-$\rm D3$-branes, and use the nilpotent superfield to project out the undesirable interaction terms as well as the unwanted degrees of freedom to end up with the standard model (not the supersymmetric version) of strong and electroweak interactions.

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arXiv2020

Linking the Supersymmetric Standard Model to the Cosmological Constant

String theory has no parameter except the string scale $M_S$, so the Planck scale $M_\text{Pl}$, the supersymmetry-breaking scale, the EW scale $m_\text{EW}$ as well as the vacuum energy density (cosmological constant) $Λ$ are to be determined dynamically at any local minimum solution in the string theory landscape. Here we consider a model that links the supersymmetric electroweak phenomenology (bottom up) to the string theory motivated flux compactification approach (top down). In this model, supersymmetry is broken by a combination of the racetrack Kähler uplift mechanism, which naturally allows an exponentially small positive $Λ$ in a local minimum, and the anti-D3-brane in the KKLT scenario. In the absence of the Higgs doublets in the supersymmetric standard model, one has either a small $Λ$ or a big enough SUSY-breaking scale, but not both. The introduction of the Higgs fields (with their soft terms) allows a small $Λ$ and a big enough SUSY-breaking scale simultaneously. Since an exponentially small $Λ$ is statistically preferred (as the properly normalized probability distribution $P(Λ)$ diverges at $Λ=0^{+}$), identifying the observed $Λ_{\rm obs}$ to the median value $Λ_{50\%}$ yields $m_{\rm EW} \sim 100$ GeV. We also find that the warped anti-D3-brane tension has a SUSY-breaking scale of $100m_{\rm EW}$ in the landscape while the SUSY-breaking scale that directly correlates with the Higgs fields in the visible sector has a value of $m_{\rm EW}$.

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arXiv2020

Multiple Ultralight Axionic Wave Dark Matter and Astronomical Structures

An ultralight scalar boson with mass $m_1 \simeq 10^{-22}$ eV is gaining credence as a Dark Matter (DM) candidate that explains the dark cores of dwarf galaxies as soliton waves. Such a boson is naturally interpreted as an axion generic in String Theory, with multiple light axions predicted in this context. We examine the possibility of soliton structures over a wide range of scales, accounting for galaxy core masses and the common presence of nuclear star clusters. We present a diagnostic soliton core mass-radius plot that provides a global view, indicating the existence of an additional axion with mass $m_2\simeq 10^{-20}$ eV, with the possibility of a third axion with mass $m_3 \gtrsim 0.5 \times 10^{-18}$ eV. We also argue that the relative mass densities measured for these axions are consistent with their cosmological production via the mis-alignment mechanism.

astro-ph.GA↗

arXiv2020

Ghostly Galaxies as Solitons of Bose-Einstein Dark Matter

The large dark cores of common dwarf galaxies are unexplained by the standard heavy particle interpretation of dark matter. This puzzle is exacerbated by the discovery of a very large but barely visible, dark matter dominated galaxy Antlia II orbiting the Milky Way, uncovered by tracking star motions with the {\t Gaia} satellite. Although Antlia II has a low mass, its visible radius is more than double any known dwarf galaxy, with an unprecedentedly low density core. We show that Antlia II favors dark matter as a Bose-Einstein condensate, for which the ground state is a stable soliton with a core radius given by the de Broglie wavelength. The lower the galaxy mass, the larger the de Broglie wavelength, so the least massive galaxies should have the widest soliton cores of lowest density. An ultra-light boson of $m_ψ\sim 1.1 \times10^{-22}$ eV, accounts well for the large size and slowly moving stars within Antlia II, and agrees with boson mass estimates derived from the denser cores of more massive dwarf galaxies. For this very light boson, Antlia II is close to the lower limiting Jeans scale for galaxy formation permitted by the Uncertainty Principle, so other examples are expected but none significantly larger in size. This simple explanation for the puzzling dark cores of dwarf galaxies implies dark matter as an ultra-light boson, such as an axion generic in String Theory.

astro-ph.CO↗

arXiv2020

Periodic Fast Radio Bursts from Axion Emission by Cosmic Superstrings

We propose that the periodic fast radio bursts of FRB 180916.J0158+65 are sourced by axion emission (mass $m_{a} \sim 10^{-14}$ eV) from cosmic superstrings. Some of the emitted axions are converted to photons by magnetic fields as they travel along the line of sight to Earth. An impulsive burst of axion emission generates a photon signal typically lasting for milliseconds and varying with frequency in the observed manner. We find a range of parameters in our cosmic string network model consistent with the properties of FRB 180916.J0158+65. We suggest followup gravitational wave observations to test our model.

astro-ph.CO↗

arXiv2020

String Landscape and Fermion Masses

Besides the string scale, string theory has no parameter except some quantized flux values; and the string theory Landscape is generated by scanning over discrete values of all the flux parameters present. We propose that a typical (normalized) probability distribution $P({\cal Q})$ of a physical quantity $\cal Q$ (with nonnegative dimension) tends to peak (diverge) at ${\cal Q}=0$ as a signature of string theory. In the Racetrack Kähler uplift model, where $P(Λ)$ of the cosmological constant $Λ$ peaks sharply at $Λ=0$, the electroweak scale (not the electroweak model) naturally emerges when the median $Λ$ is matched to the observed value. We check the robustness of this scenario. In a bottom-up approach, we find that the observed quark and charged lepton masses are consistent with the same probabilistic philosophy, with distribution $P(m)$ that diverges at $m=0$, with the same (or almost the same) degree of divergence. This suggests that the Standard Model has an underlying string theory description, and yields relations among the fermion masses, albeit in a probabilistic approach (very different from the usual sense). Along this line of reasoning, the normal hierarchy of neutrino masses is clearly preferred over the inverted hierarchy, and the sum of the neutrino masses is predicted to be $\sum m_ν \simeq 0.0592$ eV, with an upper bound $\sum m_ν <0.066$ eV. This illustrates a novel way string theory can be applied to particle physics phenomenology.

hep-th↗

arXiv2020

Dynamical Evidence of a Solitonic Core of $10^{9}M_\odot$ in the Milky Way

A wavelike solution for the non-relativistic universal dark matter (wave-DM) is rapidly gaining interest, following distinctive predictions of pioneering simulations of cosmic structure as an interference pattern of coherently oscillating bosons. A prominent solitonic standing wave is predicted at the center of every galaxy, representing the ground state, that has been identified with the wide, kpc scale dark cores of common dwarf-spheroidal galaxies, providing a boson mass of, $\simeq 10^{-22}$ eV. A denser soliton is predicted for Milky Way sized galaxies where momentum is higher, so the de Broglie scale of the soliton is smaller, $\simeq 100$ pc, of mass $\simeq 10^9 M_\odot$. Here we show the central motion of bulge stars in the Milky Way implies the presence of such a dark core, where the velocity dispersion rises inversely with radius to a maximum of $\simeq 130$ km/s, corresponding to an excess central mass of $\simeq 1.5\times 10^9 M_\odot$ within $\simeq 100$ pc, favouring a boson mass of $\simeq 10^{-22}$ eV. This quantitative agreement with such a unique and distinctive prediction is therefore strong evidence for a light bosonic solution to the long standing Dark Matter puzzle, such as the axions generic in String Theory.

astro-ph.GA↗

arXiv2019

Role of Bloch Waves in baryon-number violating processes

In the Bloch-wave approach to estimate the baryon-number-violating scattering cross section in the standard electroweak theory in the laboratory, we clarify the relation between the single sphaleron barrier and multiple (near periodic) sphaleron barrier cases. We explain how a realistic consideration modifies/corrects the idealized Bloch wave and the resonant tunneling approximation. The basic approach is in part analogous to the well-known triple-$α$ process to form carbon in nucleosynthesis.

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arXiv2018

Why the Cosmological Constant is so Small ? A String Theory Perspective

With no free parameter (except the string scale $M_S$), dynamical flux compactification in Type IIB string theory determines both the cosmological constant (vacuum energy density) $Λ$ and the Planck mass $M_P$ in terms of $M_S$, thus yielding their relation. Following elementary probability theory, we find that a good fraction of the meta-stable de Sitter vacua in the cosmic string theory landscape tend to have an exponentially small cosmological constant $Λ$ compared to either the string scale $M_S$ or the Planck scale $M_P$, i.e., $Λ\ll M_S^4 \ll M_P^4$. Here we illustrate the basic stringy ideas with a simple scalar field $ϕ^3$ (or $ϕ^4$) model coupled with fluxes to show how this may happen and how the usual radiative instability problem is bypassed (since there are no parameters to be fine-tuned). These low lying semi-classical de Sitter vacua tend to be accompanied by light scalar bosons/axions, so the Higgs boson mass hierarchy problem may be ameliorated as well.

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