Mirror Star Research Articles

Electromagnetic Signatures of Mirror Stars

Mirror stars are a generic prediction of dissipative dark matter (DM) models, including minimal atomic DM and twin baryons in the mirror twin Higgs model. Mirror stars can capture regular matter from the interstellar medium through extremely suppressed kinetic mixing interactions between the regular and the dark photon. This accumulated “nugget” will draw heat from the mirror star core and emit highly characteristic X-ray and optical signals. In this work, we devise a general parameterization of mirror star nugget properties that is independent of the unknown details of mirror star stellar physics, and use the Cloudy spectral synthesis code to obtain realistic and comprehensive predictions for the thermal emissions from optically thin mirror star nuggets. We find that mirror star nuggets populate an extremely well-defined and narrow region of the Hertzsprung–Russell diagram that only partially overlaps with the white dwarf population. Our detailed spectral predictions, which we make publicly available, allow us to demonstrate that optically thin nuggets can be clearly distinguished from white dwarf stars by their continuum spectrum shape, and from planetary nebulae and other optically thin standard sources by their highly exotic emission-line ratios. Our work will enable realistic mirror star telescope searches, which may reveal the detailed nature of DM.

Simulating Atomic Dark Matter in Milky Way Analogs

Dark sector theories naturally lead to multicomponent scenarios for dark matter where a subcomponent can dissipate energy through self-interactions, allowing it to efficiently cool inside galaxies. We present the first cosmological hydrodynamical simulations of Milky Way analogs where the majority of dark matter is collisionless cold dark matter (CDM) but a subcomponent (6%) is strongly dissipative minimal atomic dark matter (ADM). The simulations, implemented in GIZMO and utilizing FIRE-2 galaxy formation physics to model the standard baryonic sector, demonstrate that the addition of even a small fraction of dissipative dark matter can significantly impact galactic evolution despite being consistent with current cosmological constraints. We show that ADM gas with roughly standard model–like masses and couplings can cool to form a rotating “dark disk” with angular momentum closely aligned with the visible stellar disk. The morphology of the disk depends sensitively on the parameters of the ADM model, which affect the cooling rates in the dark sector. The majority of the ADM gas gravitationally collapses into dark “clumps” (regions of black hole or mirror star formation), which form a prominent bulge and a rotating thick disk in the central galaxy. These clumps form early and quickly sink to the inner ∼kiloparsec of the galaxy, affecting the galaxy’s star formation history and present-day baryonic and CDM distributions.

How to search for mirror stars with Gaia

We show for the first time how to conduct a direct search for dark matter using Gaia observations. Its public astrometric data may contain the signals of mirror stars, exotic compact objects made of atomic dark matter with a tiny kinetic mixing between the dark and SM photon. Mirror stars capture small amounts of interstellar material in their cores, leading to characteristic optical/IR and X-ray emissions. We develop the detailed pipeline for conducting a mirror star search using data from Gaia and other stellar catalogues, and demonstrate our methodology by conducting a search for toy mirror stars with a simplified calculation of their optical/IR emissions over a wide range of mirror star and hidden sector parameters. We also obtain projected exclusion bounds on the abundance and properties of mirror stars if no candidates are found, demonstrating that Gaia is a new and uniquely powerful probe of atomic dark matter. Our study provides the blueprint for a realistic mirror star search that includes a more complete treatment of the captured interstellar gas in the future.

Antistars or Antimatter Cores in Mirror Neutron Stars?

The oscillation of the neutron n into mirror neutron n′, its partner from the dark mirror sector, can gradually transform an ordinary neutron star into a mixed star consisting in part of mirror dark matter. The implications of the reverse process taking place in the mirror neutron stars depend on the sign of baryon asymmetry in the mirror sector. Namely, if it is negative, as predicted by certain baryogenesis scenarios, then n′¯−n¯ transitions create a core of our antimatter gravitationally trapped in the mirror star interior. The annihilation of accreted gas on such antimatter cores could explain the origin of γ-source candidates with an unusual spectrum compatible with baryon–antibaryon annihilation, recently identified in the Fermi LAT catalog. In addition, some part of this antimatter escaping after the mergers of mirror neutron stars can produce the flux of cosmic antihelium and also heavier antinuclei which are hunted in the AMS-02 experiment.

Neural Correlates of Motor Skill Learning Are Dependent on Both Age and Task Difficulty

Although a general age-related decline in neural plasticity is evident, the effects of age on neural plasticity after motor practice are inconclusive. Inconsistencies in the literature may be related to between-study differences in task difficulty. Therefore, we aimed to determine the effects of age and task difficulty on motor learning and associated brain activity. We used task-related electroencephalography (EEG) power in the alpha (8–12 Hz) and beta (13–30 Hz) frequency bands to assess neural plasticity before, immediately after, and 24-h after practice of a mirror star tracing task at one of three difficulty levels in healthy younger (19–24 yr) and older (65–86 yr) adults. Results showed an age-related deterioration in motor performance that was more pronounced with increasing task difficulty and was accompanied by a more bilateral activity pattern for older vs. younger adults. Task difficulty affected motor skill retention and neural plasticity specifically in older adults. Older adults that practiced at the low or medium, but not the high, difficulty levels were able to maintain improvements in accuracy at retention and showed modulation of alpha TR-Power after practice. Together, these data indicate that both age and task difficulty affect motor learning, as well as the associated neural plasticity.

How to discover Mirror Stars

Non-minimal hidden sectors are an important generic possibility and arise in well motivated theories. Thus a fraction of dark matter could have hidden interactions analogous to Standard Matter (SM) electromagnetism and nuclear physics. This leads to the formation of Mirror Stars: dark-sector analogues of regular stars that shine in dark photons. If the dark and SM photon have a small kinetic mixing, SM matter is captured in Mirror Star cores, giving rise to a dual optical and X-ray signal. This discoverable, robust and highly distinctive signature is a smoking gun of Mirror Stars.

Signatures of mirror stars

Motivated by theories of Neutral Naturalness, we argue that Mirror Stars are a generic possibility in any hidden sector with analogues of Standard Model (SM) electromagnetism and nuclear physics. We show that if there exists a tiny kinetic mixing between the dark photon and the SM photon, Mirror Stars capture SM matter from the interstellar medium, which accumulates in the core of the Mirror Star and radiates in the visible spectrum. This signature is similar to, but in most cases much fainter than, ordinary white dwarfs. We also show for the first time that in the presence of captured SM matter, a fraction of dark photons from the core of the Mirror Star convert directly to SM photons, which leads to an X-ray signal that represents a direct probe of the properties of the Mirror Star core. These two signatures together are a highly distinctive, smoking gun signature of Mirror Stars. We show that Mirror Stars could be discovered in both optical and X-ray searches up to approximately 100-1000 light years away, for a range of well-motivated values of the kinetic mixing parameter.

Association Between Lifetime Marijuana Use and Cognitive Function in Middle Age: The Coronary Artery Risk Development in Young Adults (CARDIA) Study.

Marijuana use is increasingly common in the United States. It is unclear whether it has long-term effects on memory and other domains of cognitive function. To study the association between cumulative lifetime exposure to marijuana use and cognitive performance in middle age. We used data from the Coronary Artery Risk Development in Young Adults (CARDIA) study, a cohort of 5115 black and white men and women aged 18 to 30 years at baseline from March 25, 1985, to June 7, 1986 (year 0), and followed up over 25 years from June 7, 1986, to August 31, 2011, to estimate cumulative years of exposure to marijuana (1 year = 365 days of marijuana use) using repeated measures and to assess associations with cognitive function at year 25. Linear regression was used to adjust for demographic factors, cardiovascular risk factors, tobacco smoking, use of alcohol and illicit drugs, physical activity, depression, and results of the mirror star tracing test (a measure of cognitive function) at year 2. Data analysis was conducted from June 7, 1986, to August 31, 2011. Three domains of cognitive function were assessed at year 25 using the Rey Auditory Verbal Learning Test (verbal memory), the Digit Symbol Substitution Test (processing speed), and the Stroop Interference Test (executive function). Among 3385 participants with cognitive function measurements at the year 25 visit, 2852 (84.3%) reported past marijuana use, but only 392 (11.6%) continued to use marijuana into middle age. Current use of marijuana was associated with worse verbal memory and processing speed; cumulative lifetime exposure was associated with worse performance in all 3 domains of cognitive function. After excluding current users and adjusting for potential confounders, cumulative lifetime exposure to marijuana remained significantly associated with worse verbal memory. For each 5 years of past exposure, verbal memory was 0.13 standardized units lower (95% CI, -0.24 to -0.02; P = .02), corresponding to a mean of 1 of 2 participants remembering 1 word fewer from a list of 15 words for every 5 years of use. After adjustment, we found no associations with lower executive function (-0.03 [95% CI, -0.12 to 0.07]; P = .56) or processing speed (-0.04 [95% CI, -0.16 to 0.08]; P = .51). Past exposure to marijuana is associated with worse verbal memory but does not appear to affect other domains of cognitive function.

Train the Brain: Novel Electroencephalography Data Indicate Links between Motor Learning and Brain Adaptations.

EEG differences were examined between part and whole practice in the learning of a novel motor task. Recording was done at 4 sites (i.e., O1, O2, C3, and C4) on 30 participants who performed a novel mirror star tracer task. Individuals were randomly assigned to 3 groups: whole practice, part practice, and control (no practice). Whole practice is defined as practicing a skill in its entirety. Part practice is defined as practicing separate, independent parts of the skill, and gradually combining those parts with parts that are dependent on one another. Each group was assessed during a pretest and posttest. EEG data was analyzed using a 2×2×2×3 (trials×hemisphere×site×practice) repeated measures mixed model ANOVA for each of the wave bands (lower alpha, upper alpha, lower beta, upper beta). All participants performed the task faster as no practice effect was found across the three groups; however the part practice group exhibited a significant decrease in errors. Reduced activation in the occipital and central sites was observed for lower alpha in the posttest compared to the pretest, for all participants. Hemispheric differences were present for all wavebands, with greater activation in the left hemisphere independent of practice type. The results of our study indicate that task learning was likely associated with the observed changes in the lower alpha waveband. Further, a concomitant behavior between the hemispheric lateralization of alpha and beta waveforms was observed. These results have implications for athlete training and rehabilitation. They indicate the utility of EEG for learning assessment in athletes. They also indicate learning strategies with a partial movement focus may be a beneficial strategy to support the development of complex sport skills training and rehabilitation strategies focused on reacquisition of skills prior to sport reintegration.

Cardiovascular Reactivity and Cardiometabolic Risk in Adolescents

Cardiovascular reactivity has been examined as a risk marker or factor in the pathogenesis of hypertension or cardiovascular disease, but few have examined the relationship with the metabolic syndrome. We examined whether cardiovascular reactivity to laboratory stress is associated with individual cardiometabolic risk factors and their co-occurrence. A significant positive relationship was hypothesized for both individual and clustered risk factors in their cross-sectional associations with reactivity to multiple stressors. A sample of 144, 15-17-year-old adolescents (74 % boys) largely from ethnic minority groups (54 % Hispanic White, 26 % Black) were identified at annual blood pressure (BP) screening (39 % with elevated BP) at high schools in Miami, Florida, USA. Participants completed the evaluated speaking, mirror star tracing, and cold pressor tasks, as well as cardiometabolic risk factor blood sampling. Participants were classified into metabolic syndrome criterion groups (0, 1, 2, or ≥3 criteria) based on American Heart Association adult criteria. Multiple regression analyses with individual metabolic syndrome variables demonstrated that diastolic (D)BP reactivity during the mirror star tracing task accounted for 1.3 %, 3.8 %, and 5.1 % of the respective variances in casual systolic BP, waist circumference, and triglycerides (ps < 0.05). In multinomial logistic regression models, increased DBP reactivity during mirror star tracing and cold pressor tasks, and decreased HR reactivity during the cold pressor, were associated with greater likelihood of risk factor co-occurrence (ranging from 8.3 % to 15.8 %). Findings indicate that autonomic reactivity to the mirror star tracing and cold pressor tasks, but not the evaluated speaking task, is associated with risk factor co-occurrence, and reactivity may be a clinical prognosticator of cardiometabolic disease risk.

Primordial [formula omitted] abundance implied by the mirror dark matter interpretation of the DAMA/LIBRA signal

We compute the primordial mirror helium He′ mass fraction emerging from Big Bang nucleosynthesis in the mirror sector of particles in the presence of kinetic mixing between photons and mirror photons. We explore the kinetic mixing parameter (ε) values relevant for cosmology and which are also currently probed by the dark matter direct detection experiments. In particular, we find that for ε∼10−9, as suggested by the DAMA/Libra and other experiments, a large HeO mass fraction (YHe′≈90%) is produced. Such a large value of the primordial He′ mass fraction will have important implications for the mirror dark matter interpretation of the direct detection experiments, as well as for the study of mirror star formation and evolution.

Influence of Procedural Learning on Iowa Gambling Task Performance Among HIV+ Individuals with History of Substance Dependence

HIV+ individuals have been shown to demonstrate deficits on the Iowa Gambling Task (IGT), a complex measure of "decision-making." Little remains known about what other neurocognitive processes may account for variability in IGT performance among HIV+ samples or the role of procedural learning (PL) in IGT performance. A sample of 49 HIV+ individuals with a history of substance use disorders was examined to explore the relationship between IGT performance and three measures of PL: The Rotary Pursuit, Mirror Star Tracing, and Weather Prediction tasks. We found no statistically significant relationships between IGT performance and any of the PL tasks, despite finding significant correlations among the PL tasks. This pattern of results persisted when analyzing IGT performance in various ways (e.g., performance on earlier trial blocks or impairment classifications). Although other nondeclarative processes (e.g., somatic markers) may be important for IGT performance, these findings do not support PL as an important component neurocognitive process for the IGT. Similarly, these results suggest that differences in PL performance does not account for the decision-making deficits or variability in performances observed on the IGT among HIV+ individuals with a history of substance dependence.

Deficits in complex motor functions, despite no evidence of procedural learning deficits, among HIV+ individuals with history of substance dependence.

Human immunodeficiency virus (HIV) and drugs of abuse affect common neural systems underlying procedural memory, including the striatum. The authors compared performance of 48 HIV seropositive (HIV+) and 48 HIV seronegative (HIV-) participants with history of cocaine and/or heroin dependence across multiple Trial Blocks of three procedural learning (PL) tasks: Rotary Pursuit (RP), Mirror Star Tracing (MST), and Weather Prediction (WP). Groups were well matched on demographic, psychiatric, and substance use parameters, and all participants were verified abstinent from drugs. Mixed model analyses of variance revealed that the individuals in the HIV+ group performed more poorly across all tasks, with a significant main effect of HIV serostatus observed on the Mirror Star Tracing and a trend toward significance obtained for the Rotary Pursuit task. No significant differences were observed on the Weather Prediction task. Both groups demonstrated significant improvements in performance across all three procedural learning tasks. It is important to note that no significant Serostatus x Trial Block interactions were observed on any task. Thus, the individuals in the HIV+ group tended to perform worse than those in the HIV- group across all trial blocks of procedural learning tasks with motor demands, but showed no differences in their rate of improvement across all tasks. These findings are consistent with HIV--associated deficits in complex motor skills, but not in procedural learning.

Evolutionary and structural properties of mirror star MACHOs

There can exist a hidden sector of the Universe in the form of parallel “mirror” world which has the same particle physics as the observable world and interacts with the latter only gravitationally. Big Bang nucleosynthesis bounds demand that the mirror sector should have a smaller temperature than the ordinary one. This implies that the mirror matter could play a role of dark matter, and in addition its chemical content should be dominated by helium. Here we study the evolutionary and structural properties of the mirror stars which essentially are similar to that of the ordinary stars but with higher helium contents. Being invisible in terms of photons, they could be observed only as MACHOs in the microlensing experiments. Using a numerical code, we compute evolution of stars with large helium abundances ( Y = 0.30–0.80) and a wide range of masses, from 0.5 to 10 M ⊙. We found that helium dominated mirror star should have much faster evolutionary time (up to a factor ∼30) than the ordinary star with the same mass. In addition, we show the diagrams of luminosities, effective temperatures, central temperatures and densities, and compute the masses of the He-core at ignition and the minimum mass for carbon ignition, for different chemical compositions. The general conclusion is that mirror stars evolve faster as compared to ordinary ones, and explode earlier as type II supernovae, thus enriching the galactic halo of processed mirror gas with higher metallicity, with implications for MACHO observations and galaxy evolution.

Acquisition and Retention of Motor Skills as a Function of Age and Aerobic Fitness

Evidence suggests that cognitive ability declines with advancing age but that aerobic fitness can serve to minimize or even negate these declines. The purpose of this study was to examine the relationship between age, fitness, and retention. Twenty younger (M=24.2 years) and 18 older adults (M=66.6 years) practiced on the mirror star trace until they achieved a criterion. VO2max was measured. The number of trials required to reach criterion was predicted by VO2max, p &lt; .001. and age, p &lt; .02. Retention distance was also predicted by VO2max, p &lt; .001, and age, p &lt; .001. Analysis of relative alpha change at P3 and F4 indicated that a relative increase in left-hemisphere alpha and a relative decrease in right-hemisphere alpha were associated with retention errors. Thus, older and less aerobically fit adults required more trials to reach criterion and performed less well at retention, and changes in brain activity were associated with retention errors.

Physics of mirror photons

The physics of kinetic mixing between ordinary and mirror photons is discussed. An important role is played by four linear combinations we dub the physical photon, the sterile photon, the physical mirror photon, and the sterile mirror photon. Because of the mass degeneracy between the two gauge bosons, quantum coherence effects are important. The physical photon becomes a certain coherent superposition of the bare ordinary photon and the bare mirror photon. Similarly, the physical mirror photon is another, but not orthogonal, coherent superposition. We discuss the physics of the interaction between physical mirror photons and ordinary matter. Observational signatures for some hybrid ordinary/mirror binary astrophysical systems are qualitatively discussed. We show that a small amount of ordinary matter at the center of a mirror star may make the mirror star observable. We speculate that the recently reported halo white dwarfs might actually be mirror halo stars.

Influence of cholesterol and fasting insulin levels on blood pressure reactivity.

This study examined how cholesterol and fasting insulin levels are related to blood pressure reactivity to behavioral stressors. Subjects (N = 116) were 20 to 52 years old, at 80% to 150% of ideal weight, and had an average fasting cholesterol level of 183 mg/dl. Stressor tasks included mirror star tracing and a videotaped speech task. Changes from baseline were calculated for systolic and diastolic blood pressure. Neither cholesterol nor insulin was independently related to blood pressure change scores. However, after controlling for body mass, a two-way analysis of variance revealed a significant cholesterol-by-insulin interaction for change in diastolic blood pressure (p = .022). Subjects in the high-cholesterol/high-insulin group showed the greatest increase in diastolic blood pressure reactivity. In a general population, people with a below-average cholesterol level experience only moderate cardiovascular reactivity to mental stressors regardless of their fasting insulin level. However, for people with an above-average cholesterol level, fasting insulin level is an important factor in determining potential reactivity to mental stressors. These findings highlight the importance of adequate sample size to allow for the analysis of such interactions in future studies of cholesterol, insulin, and blood pressure reactivity.

Cosmic gamma-ray bursts

The properties of the cosmic Gamma-ray Bursts (GRBs) are briefly summarized. A detailed bibliography is given with titles of the papers. Two fundamental theoretical problems are pointed out: the problem of the energy source, and the problem of compactness. I demonstrate some inconsistencies in the estimates of the fireball optical thickness that are widely used in the discussion of the latter problem. The possible connection of GRBs with the Dark Matter candidates is mentioned. I argue that GRBs can be produced by collapses or mergers of stars made of one probable Dark Matter candidate, namely the mirror particles. I speculate on the impact that the parameters of the neutrino oscillations might have on the observed properties of GRBs if the latter are the products of mirror star deaths.

Menstrual cycle, race and task effects on blood pressure recovery from acute stress

This study examined cardiovascular recovery from two standardized laboratory stressors in 68 healthy black and white normotensive women and men (mean age 33 years). Women were studied in a randomized order at the same time of day on two separate occasions, once during the follicular phase (days 7 to 10 following menses) and once during the luteal phase (days 7 to 10 following the leutenizing-hormone surge) of the menstrual cycle. Men were studied twice approximately 6 weeks apart. There were differential effects of the tasks on blood pressure recovery (change scores) with a mirror star task yielding poorer diastolic blood pressure recovery ( p=0.004) and an interpersonal speaking task yielding poorer systolic blood pressure recovery ( p=0.003). Across both tasks, blacks evidenced greater diastolic blood pressure recovery as compared to whites ( p=0.02). Black women showed greater diastolic blood pressure recovery in the luteal as compared to the follicular phase ( p=0.01), whereas white women evidenced no such change across the menstrual cycle. Correlation analysis across testing sessions generally revealed comparable temporal stability values for recovery as compared to reactivity measures. The findings support prior studies indicating racial differences in recovery from acute stress and extend these findings by suggesting that the menstrual cycle may differentially affect recovery in black versus white women.

Motor Performance and Motor Learning as a Function of Age and Fitness

Past studies have shown that electroencephalographic alpha activity increases as people learn to perform a novel motor task. Additionally, it has been suggested that motor performance and learning decline as people age beyond 60 years, and it has been hypothesized that physical fitness may attenuate this decline through its impact on the cerebral environment. This study was designed to replicate past research by assessing changes in alpha activity as a function of learning and to extend past research by examining differences in motor performance, motor learning, and alpha activity as a function of age and fitness. VO2max was assessed in 41 older (ages 60–80 years) and 42 younger (ages 20–30 years) participants. Participants were randomly assigned to experimental or control conditions, which differed in the amount of practice received. Participants performed trials on the mirror star trace on both an acquisition and a retention day. Results indicated that younger participants performed better and had greater learning than older participants. Fitness was not found to impact either performance or learning. Participants in the experimental group improved more than those in the control group and maintained this difference at retention, which suggests that learning occurred. Associated with these improvements in performance capabilities was an increase in alpha power.