arXiv subjects

L. C. R. Wijewardhana

Publications and source records attributed to L. C. R. Wijewardhana.

At least 19 recordsLinked to original sources

arXiv2026

The signals of doomsday II: Cosmological signatures of late time $SU(3)_c$ symmetry breaking

Only two gauge symmetries remain unbroken today: $SU(3)_c$ and $U(1)_{\rm EM}$. Both are crucial to our universe as it is and to our form of life. Unless we are special observers at the end of the cosmological symmetry-breaking chain, there is no reason they must remain unbroken forever. We investigate the cosmological signatures of late-time $SU(3)_c$ breaking in our model with a new colored scalar whose potential supports a first-order phase transition through true-vacuum bubble nucleation. We analyze three physically distinct production mechanisms of the expanding bubble wall. The first is direct nonthermal production from vacuum mismatch across the accelerating wall in the scalar and massive-gluon sectors. The second arises from frictional dissipation into a shocked layer. Including the finite-temperature effective potential, we show that our benchmark critical temperature $T_c$ is below the massive-gluon and scalar masses; an equilibrated relativistic broken-phase thermal bath would therefore restore $SU(3)_c$. We formulate a subcritical thermal freeze-out estimate below $T_c$, where massive broken-phase particles can still be produced but only with Boltzmann suppression. The third is a non-equilibrium wall--matter transition-radiation channel: ambient baryonic matter crossing the relativistic wall can radiate broken-phase massive gluons and scalar excitations. This requires no thermal bath above $T_c$ and can also continue after the wall reaches terminal velocity. We study the decays of the physical color-octet scalar and massive gluons, using \texttt{Pythia} to hadronize their decay products and determine the resulting photon and neutrino spectra. If the wall reaches a subluminal terminal velocity, these particles can arrive before the wall. The resulting high-energy spectra are a long-range observational signature that, if observed, could signal cosmic doomsday.

hep-ph↗

arXiv2025

Higher-Dimensional Chirally Stabilized Fixed Points and Their Deformations

Non-Fermi liquids in $d>2$ remain poorly understood, particularly when relevant perturbations destabilize them. In one spatial dimension, chirally stabilized fixed points provide a rare class of analytically tractable non-Fermi-liquid critical points, but their higher-dimensional analogues have been elusive. Here, we develop a Wilsonian operator-product-expansion renormalization group scheme that captures power-divergent terms and use it to construct finite-$N$ higher-dimensional analogues of chirally stabilized fixed points in arbitrary dimension $d\le4$. This exposes a conformal window at finite $N$. We further show that symmetry-breaking masses, far from being trivial, can collapse this window and drive the system to strong coupling, triggering dynamical mass generation.

cond-mat.str-el↗

arXiv2025

Multi-axion like description of the dark sector in light of the Hubble and $σ_8$ tensions

Local methods of direct determination of the Hubble constant and $σ_8$ seem to conflict with the predictions made from the cosmic microwave background and $Λ$CDM. We propose a proof-of-concept model that models portions of the dark sector as several coupled axion-like fields, resulting in both early and late time departures from $Λ$CDM. We determine that the model successfully eliminates both the Hubble and $σ_8$ tensions, while remaining consistent with both the DESI survey and the BAO sound horizon.

astro-ph.CO↗

arXiv2024

Dynamics of Inspiraling Dark Energy

We investigate the dynamics of a multifield dark energy model, which arises from certain rapid-turning and inspiraling trajectories in field space. We find the speed of sound $c_s$ of the dark energy perturbations around the background and show that $c_s$ is monotonically decreasing with time. Furthermore, it has a positive-definite lower bound that implies a certain clustering scale. We also extend the previously known background solution for dark energy to an exact solution that includes matter. This allows us to address the implications of our model for two cosmological tensions. More precisely, we argue that the $σ_8$ tension can be alleviated generically, while reducing the Hubble tension requires certain constraints on the parameter space of the model. Notably, a necessary condition for alleviating the Hubble tension is that the transition from matter domination to the dark energy epoch begins earlier than in $Λ$CDM.

hep-th↗

arXiv2023

WKB approximation to boson dark matter

Galactic dark matter halos may be composed of ultralight axions (ULAs) ($m_a \lesssim 1$ eV) with wave functions that satisfy nonlinear Schrödinger-Poisson equations (SPA). We find eigenstates of SPA in WKB approximation. The expansion parameter of the WKB approximation is $δ=1/\sqrt{S}$, where $S=2 M R G m_a^{2}$, with $M$ being the total mass, $R$ the radius of the halo, and $G$ the gravitational constant. $S\gg 1$ for almost all galaxies, even if the ULA mass is as small as $m_a=10^{-22} $ eV, making the leading order WKB approximation almost exact. As the level spacing of bound states is roughly proportional to $δ$, the number of states in the gravitational well is huge. We do not see a reason why not all or most of them contribute to the halo. Using an appropriate distribution function allows the summation of states to construct the profile of the halo as a function of the gravitational potential, which can be found solving the Poisson equation. Using various energy distribution functions, we obtain results similar to those in simulations. Future plans include investigations of collapse through time dependent generalizations, and inclusion of self-interactions, which also induce decay processes of the halo.

astro-ph.GA↗

arXiv2022

Testing multiflavored ULDM models with SPARC

We perform maximum likelihood estimates (MLEs) for single and double flavor ultralight dark matter (ULDM) models using the Spitzer Photometry and Accurate Rotation Curves (SPARC) database. These estimates are compared to MLEs for several commonly used cold dark matter (CDM) models. By comparing various CDM models we find, in agreement with previous studies, that the Burkert and Einasto models tend to perform better than other commonly used CDM models. We focus on comparisons between the Einasto and ULDM models and analyze cases for which the ULDM particle masses are: free to vary; and fixed. For each of these analyses, we perform fits assuming the soliton and halo profiles are: summed together; and matched at a given radius. When we let the particle masses vary, we find a negligible preference for any particular range of particle masses, within $10^{-25}\,\text{eV}\leq m\leq10^{-19}\,\text{eV}$, when assuming the summed models. For the matched models, however, we find that almost all galaxies prefer particles masses in the range $10^{-23}\,\text{eV}\lesssim m\lesssim10^{-20}\,\text{eV}$. For both double flavor models we find that most galaxies prefer approximately equal particle masses. We find that the summed models give much larger variances with respect to the soliton-halo (SH) relation than the matched models. When the particle masses are fixed, the matched models give median and mean soliton and halo values that fall within the SH relation bounds, for most masses scanned. When the particle masses are fixed in the fitting procedure, we find the best fit results for the particle mass $m=10^{-20.5}\,\text{eV}$ (for the single flavor models) and $m_1=10^{-20.5}\,\text{eV}$, $m_2=10^{-20.2}\,\text{eV}$ for the double flavor, matched model. We discuss how our study will be furthered using a reinforcement learning algorithm.

astro-ph.CO↗

arXiv2022

Dark Energy from Inspiraling in Field Space

We find an exact solution of the equations of motion of a two-field cosmological model, which realizes multi-field dark energy. The latter is characterized by field-space trajectories with turning rates that are always large. We study a class of two-field models and show that it is possible to have such trajectories, giving accelerated space-time expansion, even when the scalar potential preserves the rotational invariance of the field-space metric. For the case of Poincaré-disk field space, we derive the form of the scalar potential compatible with such background solutions and, furthermore, we find the exact solutions analytically. Their field-space trajectories are spirals inward, toward the center of the Poincaré disk. Interestingly, the functional form of the relevant scalar potential is compatible with a certain hidden symmetry, although the latter is broken by the presence of a constant term.

hep-th↗

arXiv2022

RG Flow and Symmetry Breaking in a Weakly Coupled Model

We explore a weakly coupled $SU(N_{c})$ gauge theory, examining its fixed-point structure and the transition from infrared conformality to spontaneous symmetry breaking. Following a previous study, we couple the gauge field to $N_s$ scalars and $N_f$ fermions, take the large-$N_c$ limit with $N_s/N_c$ and $N_f/N_c$ fixed, and adjust these ratios to produce weakly coupled infrared fixed points while maintaining asymptotic freedom. We map out renormalization-group trajectories, and describe the transition to symmetry breaking as the ratio $N_s/N_c$ is increased. We examine the breaking by employing the one-loop effective potential. At tree level, a scalar-field vacuum expectation value (VEV) of a certain form is allowed, leading to masses for a subset of the scalar fields. Among the remaining massless scalars, one corresponds to a massless dilaton and the others are Nambu-Goldstone bosons absorbed by the gauge fields. The one-loop potential breaks the scale symmetry explicitly, determining the VEV and generating a dilaton mass suppressed relative to the other masses by a factor of the weak scalar coupling.

hep-th↗

arXiv2021

Interacting dark energy axions in light of the Hubble tension

A current problem within the ΛCDM framework is the tension between late and early time measurements of the Hubble parameter today, H0. We entertain the possibility that dark energy modeled as multiple interacting axion-like-particle species can alleviate the current Hubble tension. We then test these parameters against the milder tension between the CMB and large scale structure (LSS) observations of σ8 to ensure that these models do not exacerbate the tension. We find that there exist parameter spaces for models of two and three axion-like-particles which can potentially alleviate the Hubble tension as well as the σ8 tension.

astro-ph.CO↗

arXiv2021

Global View of Axion Stars with (Nearly) Planck-Scale Decay Constants

We show that axion stars formed from axions with nearly Planck-scale decay constants $f$ are unstable to decay, and are unlikely to have phenomenological consequences. More generally, we show how results at smaller $f$ cannot be naively extrapolated to $f=\mathcal{O}(M_P)$ as, contrary to conventional wisdom, gravity and special relativity can both become relevant in the same regime. We clarify the rate of decay by reviewing and extending previous work on oscillons and axion stars, which imply a fast decay rate even for so-called dilute states at large $f$.

hep-ph↗

arXiv2021

Using atomic clocks to detect local dark matter halos

It is possible that bosonic dark matter forms halos around the Sun or the Earth. We discuss the possibility of probing such halos with atomic clocks. Focusing on either a Higgs portal or photon portal interaction between the dark matter and the Standard Model, we search the possible parameter space for which a clock on Earth and a clock in space would have a discernible frequency difference. Bosonic dark matter halos surrounding the Earth can potentially be probed with current optical atomic clocks.

hep-ph↗

arXiv2021

Density profile of multi-state fuzzy dark matter

Equations of motion for excited states of weakly self-interacting bosons forming fuzzy dark matter are solved using the WKB approximation. The contribution of self-interactions are neglected in the equations of motion. Wave functions of excited states are expressed in terms of a yet undetermined gravitational potential. At equilibrium, the contributions of states to the density distribution are summed using Bose-Einstein statistics. Combined with the Poisson equation, a differential equation is obtained for the gravitational potential, which has physically acceptable solutions only if the energy spectrum of excited states has a finite gap, corresponding to a finite virial radius. Such a gap could be created by decay processes, in first order perturbation of the self-interaction potential. The obtained density profile is found to be similar to the Burkert profile.

hep-ph↗

arXiv2020

Galactic Condensates composed of Multiple Axion Species

Ultralight scalar dark matter has been proposed to constitute a component of dark matter, though the minimal scenarios have increasingly become constrained. In this work, we analyze scenarios where the dark matter consists of more than one ultralight boson, each with different masses. This potentially leads to formation of gravitationally-bound Bose-Einstein condensates with structures that are very different from condensates composed of a single scalar field. By generalizing from the well-understood single-flavor case, we explore a large range of input parameters, subject to stability criteria, and determine the allowed parameter space for two-flavor condensates as a function of particle physics parameters, paying particular attention to cases where such condensates could compose galactic cores. We also analyze single-flavor condensates subject to external gravity from massive inner bodies and find that such systems may mimic the size of galactic cores as well.

hep-ph↗

arXiv2020

Probing Bosonic Stars with Atomic Clocks

Dark Matter could potentially manifest itself in the form of asymmetric dark stars. In this paper we entertain the possibility of probing such asymmetric bosonic dark matter stars by the use of atomic clocks. If the dark sector connects to the standard model sector via a Higgs or photon portal, the interior of boson stars that are in a Bose-Einstein condensate state can change the values of physical constants that control the timing of atomic clock devices. Dilute asymmetric dark matter boson stars passing through the Earth can induce frequency shifts that can be observed in separated Earth based atomic clocks. This gives the opportunity to probe a class of dark matter candidates that for the moment cannot be detected with any different conventional method.

hep-ph↗

arXiv2019

Global view of QCD axion stars

Taking a comprehensive view, including a full range of boundary conditions, we reexamine QCD axion star solutions based on the relativistic Klein-Gordon equation (using the Ruffini-Bonazzola approach) and its non-relativistic limit, the Gross-Pitaevskii equation. A single free parameter, conveniently chosen as the central value of the wavefunction of the axion star, or alternatively the chemical potential with range $-m<μ< 0$ (where $m$ is the axion mass), uniquely determines a spherically-symmetric ground state solution, the axion condensate. We clarify how the interplay of various terms of the Klein-Gordon equation determines the properties of solutions in three separate regions: the structurally stable (corresponding to a local energy minimum) dilute and dense regions, and the intermediate, structurally unstable transition region. From the Klein-Gordon equation, one can derive alternative equations of motion including the Gross-Pitaevskii and Sine-Gordon equations, which have been used previously to describe axion stars in the dense region. In this work, we clarify precisely how and why such methods break down as the binding energy increases, emphasizing the necessity of using the full relativistic Klein-Gordon approach. Finally, we point out that, even after including perturbative axion number violating corrections, solutions to the equations of motion, which assume approximate conservation of axion number, break down completely in the regime with strong binding energy, where the magnitude of the chemical potential approaches the axion mass.

hep-ph↗

arXiv2018

Stability of Condensed Fuzzy Dark Matter Halos

Stability properties of gravitationally bound condensates composed of ultralight axionic Fuzzy Dark Matter (FDM) are studied. Previous work has shown that astrophysical collisions could make self-gravitating condensates structurally unstable, making them prone to collapse and decay; in the context of FDM, we reexamine the relevant timescales using the time-dependent variational method. We show that FDM condensates can be made unstable through gravitational interactions with central black holes, for black hole masses in a phenomenologically relevant range. Instability could also be stimulated by galaxy collisions. The subsequent decay takes place over a period lasting as long as many thousands of years. We also discuss the possible relevance of FDM condensates to understanding the composition of Ultracompact Dwarf (UCD) Galaxies. Future observation of extremely massive black holes in the central regions of UCDs can constrain this interpretation.

astro-ph.CO↗

arXiv2018

On Approximation Methods in the Study of Boson Stars

We analyze the accuracy of the variational method in computing physical quantities relevant for gravitationally bound Bose-Einstein condensates. Using a variety of variational ansätze found in existing literature, we determine physical quantities and compare them to exact numerical solutions. We conclude that a "linear+exponential" wavefunction proportional to $(1 + ξ)\exp(-ξ)$ (where $ξ$ is a dimensionless radial variable) is the best fit for attractive self-interactions along the stable branch of solutions, while for small particle number $N$ it is also the best fit for repulsive self-interactions. For attractive self-interactions along the unstable branch, a single exponential is the best fit for small $N$, while a sech wavefunction fits better for large $N$. The Gaussian wavefunction ansatz, which is used often in the literature, is exceedingly poor across most of the parameter space, with the exception of repulsive interactions for large $N$. We investigate a "double exponential" ansatz with a free constant parameter, which is computationally efficient and can be optimized to fit the exact solutions in different limits. We show that the double exponential can be tuned to fit the sech ansatz, which is computationally slow. We also show how to generalize the addition of free parameters in order to create more computationally efficient ansätze using the double exponential. Determining the best ansatz, according to several comparison parameters, will be important for analytic descriptions of dynamical systems. Finally, we examine the underlying relativistic theory, and critically analyze the Thomas-Fermi approximation often used in the literature.

hep-ph↗

arXiv2018

Classical Nonrelativistic Effective Field Theory and the Role of Gravitational Interactions

Coherent oscillation of axions or axion-like particles may give rise to long-lived clumps, called axion stars, because of the attractive gravitational force or its self-interaction. Such a kind of configuration has been extensively studied in the context of oscillons without the effect of gravity, and its stability can be understood by an approximate conservation of particle number in a non-relativistic effective field theory (EFT). We extend this analysis to the case with gravity to discuss the longevity of axion stars and clarify the EFT expansion scheme in terms of gradient energy and Newton's constant. Our EFT is useful to calculate the axion star configuration and its classical lifetime without any ad hoc assumption. In addition, we derive a simple stability condition against small perturbations. Finally, we discuss the consistency of other non-relativistic effective field theories proposed in the literature.

hep-ph↗