arXiv subjects

John H. Simonetti

Publications and source records attributed to John H. Simonetti.

15 recordsLinked to original sources

arXiv2022

Stability and Observability of Magnetic Primordial Black Hole-Neutron Star Collisions

The collision of a primordial black hole with a neutron star results in the black hole eventually consuming the entire neutron star. However, if the black hole is magnetically charged, and therefore stable against decay by Hawking radiation, the consequences can be quite different. Upon colliding with a neutron star, a magnetic black hole very rapidly comes to a stop. For large enough magnetic charge, we show that this collision can be detected as a sudden change in the rotation period of the neutron star, a glitch or anti-glitch.We argue that the magnetic primordial black hole, which then settles to the core of the neutron star, does not necessarily devour the entire neutron star; the system can instead reach a long-lived, quasi-stable equilibrium. Because the black hole is microscopic compared to the neutron star, most stellar properties remain unchanged compared to before the collision. However, the neutron star will heat up and its surface magnetic field could potentially change, both effects potentially observable.

astro-ph.HE↗

arXiv2022

Quantum Gravity and Phenomenology: Dark Matter, Dark Energy, Vacuum Selection, Emergent Spacetime, and Wormholes

We discuss the relevance of quantum gravity to the frontier questions in high energy phenomenology: the problems of dark matter, dark energy, and vacuum selection as well as the problems of emergent spacetime and wormholes. Dark matter and dark energy phenomenology, and the problem of vacuum selection are discussed within the context of string theory as a model of quantum gravity. Emergent spacetime and wormholes are discussed in a more general context of effective theories of quantum gravity.

hep-th↗

arXiv2021

Positive attitudinal shifts and a narrowing gender gap: Do expertlike attitudes correlate to higher learning gains for women in the physics classroom?

A large body of research shows that using interactive engagement pedagogy in the introductory physics classroom consistently results in significant student learning gains; however, with a few exceptions, those learning gains tend not to be accompanied by more expertlike attitudes and beliefs about physics and learning physics. In fact, in both traditionally taught and active learning classroom environments, students often become more novicelike in their attitudes and beliefs following a semester of instruction. Further, prior to instruction, men typically score higher than women on conceptual inventories, such as the Force Concept Inventory (FCI), and more expertlike on attitudinal surveys, such as the Colorado Learning Attitudes about Science Survey (CLASS), and those gender gaps generally persist following instruction. In this paper, we analyze three years of pre-post matched data for physics majors at Virginia Tech on the FCI and the CLASS. The courses were taught using a blended pedagogical model of peer instruction, group problem solving, and direct instruction, along with an explicit focus on the importance of conceptual understanding and a growth mindset. We found that the FCI gender gap decreased, and both men and women showed positive, expertlike shifts on the CLASS. Perhaps most surprisingly, we found a meaningful correlation between a student's post- CLASS score and normalized FCI gain for women, but not for men.

physics.ed-ph↗

arXiv2020

Accessing the axion via compact object binaries

Black holes in binaries with other compact objects can provide natural venues for indirect detection of axions or other ultralight fields. The superradiant instability associated with a rapidly spinning black hole leads to the creation of an axion cloud which carries energy and angular momentum from the black hole. This cloud will then decay via gravitational wave emission. We show that the energy lost as a result of this process tends toward an outspiraling of the binary orbit. A given binary system is sensitive to a narrow range of axion masses, determined by the mass of the black hole. Pulsar-black hole binaries, once detected in the electromagnetic band, will allow high-precision measurements of black hole mass loss via timing measurements of the companion pulsar. This avenue of investigation is particularly promising in light of the recent preliminary announcements of two candidate black hole-neutron star mergers by LIGO/VIRGO (#S190814bv and #S190426c). We demonstrate that for such a binary system with a typical millisecond pulsar and a 3-solar-mass black hole, axions with masses between $2.7 \times 10^{-12}$ eV and $3.2 \times 10^{-12}$ eV are detectable. Recent gravitational wave observations by LIGO/VIRGO of binary black hole mergers imply that, for these binaries, gravitational radiation from the rotating quadrupole moment is a dominant effect, causing an inspiraling orbit. With some reasonable assumptions about the period of the binary when it formed and the spins of the black holes, these observations rule out possible axion masses between $3 \times 10^{-13}$ eV and $6 \times 10^{-13}$ eV. Future binary black hole observations, for example by LISA, are expected to provide more robust bounds. In some circumstances, neutron stars may also undergo superradiant instabilities, and binary pulsars could be used to exclude axions with certain masses and matter couplings.

astro-ph.HE↗

arXiv2020

A sensitive search for wormholes

The realm of strong classical gravity and perhaps even quantum gravity are waiting to be explored. In this letter we consider the recently detected triple system composed of two stars and a non-accreting black hole. Using published observations of this system we conduct the most sensitive test to date for whether the black hole is actually a wormhole by looking for orbital perturbations due to an object on the other side of the wormhole. The mass limit obtained on the perturber is $\sim4$ orders of magnitude better than for observations of S2 orbiting the supermassive black hole at Sgr A*. We also consider how observations of a pulsar could test for whether the black hole in a pulsar-black hole binary is a wormhole. A pulsar in a similar orbit to S2 would be $\sim10$ orders of magnitude more sensitive than observations of S2. For a nominal pulsar-black hole binary of stellar masses, with orbital size similar to that of the Hulse-Taylor binary pulsar, one year of observations could set a mass limit on a perturber that is $\sim6$ orders of magnitude better than observations of a pulsar around Sgr~A*. A range of limits between the pulsar-Sgr~A* and Hulse-Taylor cases could be obtained for a possible population of pulsar-black hole binaries that may exist near the galactic center.

gr-qc↗

arXiv2017

Shining Light on Quantum Gravity with Pulsar-Black Hole Binaries

Pulsars are some of the most accurate clocks found in nature, while black holes offer a unique arena for the study of quantum gravity. As such, pulsar-black hole (PSR-BH) binaries provide ideal astrophysical systems for detecting the effects of quantum gravity. With the success of aLIGO and the advent of instruments like the SKA and eLISA, the prospects for the discovery of such PSR-BH binaries are very promising. We argue that PSR-BH binaries can serve as ready-made testing grounds for proposed resolutions to the black hole information paradox. We propose using timing signals from a pulsar beam passing through the region near a black hole event horizon as a probe of quantum gravitational effects. In particular, we demonstrate that fluctuations of the geometry outside a black hole lead to an increase in the measured root mean square deviation of the arrival times of pulsar pulses traveling near the horizon. This allows for a clear observational test of the nonviolent nonlocality proposal for black hole information escape. For a series of pulses traversing the near-horizon region, this model predicts an rms in pulse arrival times of $\sim30\ μ$s for a $3 M_\odot$ black hole, $\sim0.3\, $ms for a $30 M_\odot$ black hole, and $\sim40\, $s for Sgr A*. The current precision of pulse time-of-arrival measurements is sufficient to discern these rms fluctuations. This work is intended to motivate observational searches for PSR-BH systems as a means of testing models of quantum gravity.

hep-th↗

arXiv2017

Analysis of Scattering from Archival Pulsar Data using a CLEAN-based Method

In this work we adopted a CLEAN-based method to determine the scatter time, $τ$, from archived pulsar profiles under both the thin screen and uniform medium scattering models and to calculate the scatter time frequency scale index $α$ where $τ\proptoν^α$. The value of $α$ is $-4.4$, if a Kolmogorov spectrum of the interstellar medium turbulence is assumed. We deconvolved 1342 profiles from 347 pulsars over a broad range of frequencies and dispersion measures. In our survey, in the majority of cases the scattering effect was not significant compared to pulse profile widths. For a subset of 21 pulsars scattering at the lowest frequencies was large enough to be measured. Because reliable scatter time measurements were determined only for the lowest frequency, we were limited to using upper limits on scatter times at higher frequencies for the purpose of our scatter time frequency slope estimation. We scaled the deconvolved scatter time to 1~GHz assuming $α=-4.4$ and considered our results in the context of other observations which yielded a broad relation between scatter time and dispersion measure.

astro-ph.HE↗

arXiv2016

Constraining the Rate of Primordial Black-Hole Explosions and Extra Dimension Scale using a Low-Frequency Radio Antenna Array

An exploding primordial black-hole (PBH) may produce a single pulse of electromagnetic radiation detectable at the low-frequency end of the radio spectrum. Furthermore, a radio transient from an exploding PBH could be a signature of an extra spatial dimension. We describe here an approach for searching for PBH explosions using a low-frequency radio antenna array, and as a practical example, the results of a such a search using the Eight-meter-wavelength Transient Array (ETA). No compelling astrophysical signal was detected in $\approx 4$ hours of data implying an observational upper limit on the rate of exploding PBHs is $4.2 \times 10^{-7} \,\rm{pc}^{-3}\,\rm{yr}^{-1}$ for an exploding PBH with a fireball Lorentz factor of $10^{4.5}$ for the standard scenario of Page and Hawking. This rate limit is the strongest constraint yet set for PBH explosions with this fireball Lorentz factor. Observations ($\sim300$ hours) using the Arecibo Observatory were used to set a stronger constraint on the rate of PBH explosions for a fireball Lorentz factor of $10^{4.6}$ but the limit set by those observations for the fireball Lorentz factor considered here are less stringent by more than an order of magnitude. The limits considered here are applicable to exploding PBHs in the halo of the Galaxy. These observations also imply an upper limit of $2.0 \times 10^{-4} \,\rm{pc}^{-3}\,\rm{yr}^{-1}$ on the rate of PBH explosions in the context of certain extra dimension models as described by Kavic et al. This rate limit is for a fireball Lorentz factor of $10^{4.3}$ which corresponds to an extra dimension compactification scale of $3.0 \times 10^{-18}$m.

astro-ph.HE↗

arXiv2016

Simultaneous Observations of Giant Pulses from Pulsar PSR B0031-07 at 38 MHz and 74 MHz

The first station of the Long Wavelength Array (LWA1) was used to study PSR~B0031-07 with simultaneous observations at 38 and 74~MHz. We found that 158 (0.35\%) of the observed pulses at 38~MHz and 221 (0.49\%) of the observed pulses at 74~MHz qualified as giant pulses in a total of 12 hours of observations. Giant pulses are defined as having flux densities of a factor of $\geq$ 90 times that of an average pulse at 38~MHz and $\geq$ 80 times that of an average pulse at 74~MHz. The cumulative distribution of pulse strength follows a power law, with an index of $-$4.2 at 38~MHz and $-$4.9 at 74~MHz. This distribution has a much more gradual slope than would be expected if observing the tail of a Gaussian distribution of normal pulses. The dispersion measure value which resulted in the largest signal-to-noise for dedispersed pulses was DM $=10.9$~pc~cm$^{-3}$. No other transient pulses were detected in the data in the wide dispersion measure range from 1 to 5000~pc~cm$^{-3}$. There were 12 giant pulses detected within the same period from both 38 and 74~MHz, meaning that the majority of them are not generated in a wide band.

astro-ph.HE↗

arXiv2015

Multi-messenger astronomy of gravitational-wave sources with flexible wide-area radio transient surveys

We explore opportunities for multi-messenger astronomy using gravitational waves (GWs) and prompt, transient low-frequency radio emission to study highly energetic astrophysical events. We review the literature on possible sources of correlated emission of gravitational waves and radio transients, highlighting proposed mechanisms that lead to a short-duration, high-flux radio pulse originating from the merger of two neutron stars or from a superconducting cosmic string cusp. We discuss the detection prospects for each of these mechanisms by low-frequency dipole array instruments such as LWA1, LOFAR and MWA. We find that a broad range of models may be tested by searching for radio pulses that, when de-dispersed, are temporally and spatially coincident with a LIGO/Virgo GW trigger within a $\usim 30$ second time window and $\usim 200 \mendash 500 \punits{deg}^{2}$ sky region. We consider various possible observing strategies and discuss their advantages and disadvantages. Uniquely, for low-frequency radio arrays, dispersion can delay the radio pulse until after low-latency GW data analysis has identified and reported an event candidate, enabling a \emph{prompt} radio signal to be captured by a deliberately targeted beam. If neutron star mergers do have detectable prompt radio emissions, a coincident search with the GW detector network and low-frequency radio arrays could increase the LIGO/Virgo effective search volume by up to a factor of $\usim 2$. For some models, we also map the parameter space that may be constrained by non-detections.

astro-ph.HE↗

arXiv2015

Observations of Giant Pulses from Pulsar PSR B0950+08 using LWA1

We report the detection of giant pulse emission from PSR B0950+08 in 24 hours of observations made at 39.4 MHz, with a bandwidth of 16 MHz, using the first station of the Long Wavelength Array, LWA1. We detected 119 giant pulses from PSR B0950+08 (at its dispersion measure), which we define as having SNRs at least 10 times larger than for the mean pulse in our data set. These 119 pulses are 0.035% of the total number of pulse periods in the 24 hours of observations. The rate of giant pulses is about 5.0 per hour. The cumulative distribution of pulse strength $S$ is a steep power law, $N(>S)\propto S^{-4.7}$, but much less steep than would be expected if we were observing the tail of a Gaussian distribution of normal pulses. We detected no other transient pulses in a dispersion measure range from 1 to 90 pc cm$^{-3}$, in the beam tracking PSR B0950+08. The giant pulses have a narrower temporal width than the mean pulse (17.8 ms, on average, vs. 30.5 ms). The pulse widths are consistent with a previously observed weak dependence on observing frequency, which may be indicative of a deviation from a Kolmogorov spectrum of electron density irregularities along the line of sight. The rate and strength of these giant pulses is less than has been observed at $\sim$100 MHz. Additionally, the mean (normal) pulse flux density we observed is less than at $\sim$100 MHz. These results suggest this pulsar is weaker and produces less frequent giant pulses at 39 MHz than at 100 MHz.

astro-ph.HE↗

arXiv2012

A Precision Test for an Extra Spatial Dimension Using Black Hole--Pulsar Binaries

We discuss the observable effects of enhanced black-hole mass loss in a black hole--neutron star (BH--NS) binary, due to the presence of a warped extra spatial dimension of curvature radius $L$ in the braneworld scenario. For some masses and orbital parameters in the expected ranges the binary components would outspiral, the opposite of the behavior due to energy loss from gravitational radiation alone. If the NS is a pulsar, observations of the rate of change of the orbital period with a precision obtained for the Binary Pulsar B1913+16 could easily detect the effect of mass loss. For $M_{BH}=7M_\odot$, $M_{NS}=1.4M_\odot$, eccentricity $e=0.1$, and $L=10μ$m, the critical orbital period dividing systems which inspiral from systems which outspiral is P$\approx$6.5 hours, which is within the range of expected orbital periods; this value drops to P$\approx$4.2 hours for $M_{BH}=5M_\odot$. Observations of a BH--pulsar system could set considerably better limits on $L$ in these braneworld models than could be determined by torsion-balance gravity experiments in the foreseeable future.

astro-ph.HE↗

arXiv2008

Transient Pulses from Exploding Primordial Black Holes as a Signature of an Extra Dimension

An evaporating black hole in the presence of an extra spatial dimension would undergo an explosive phase of evaporation. We show that such an event, involving a primordial black hole, can produce a detectable, distinguishable electromagnetic pulse, signaling the existence of an extra dimension of size $L\sim10^{-18}-10^{-20}$ m. We derive a generic relationship between the Lorentz factor of a pulse-producing "fireball" and the TeV energy scale. For an ordinary toroidally compactified extra dimension, transient radio-pulse searches probe the electroweak energy scale ($\sim$0.1 TeV), enabling comparison with the Large Hadron Collider.

astro-ph↗

arXiv2008

Searching for Transient Pulses with the ETA Radio Telescope

Array-based, direct-sampling radio telescopes have computational and communication requirements unsuited to conventional computer and cluster architectures. Synchronization must be strictly maintained across a large number of parallel data streams, from A/D conversion, through operations such as beamforming, to dataset recording. FPGAs supporting multi-gigabit serial I/O are ideally suited to this application. We describe a recently-constructed radio telescope called ETA having all-sky observing capability for detecting low frequency pulses from transient events such as gamma ray bursts and primordial black hole explosions. Signals from 24 dipole antennas are processed by a tiered arrangement of 28 commercial FPGA boards and 4 PCs with FPGA-based data acquisition cards, connected with custom I/O adapter boards supporting InfiniBand and LVDS physical links. ETA is designed for unattended operation, allowing configuration and recording to be controlled remotely.

astro-ph↗

arXiv2002

Galactic Foregrounds in OVRO and UCSB South Pole 1994 Cosmic Microwave Background Anisotropy Data

We study Galactic emission foreground contamination of the OVRO and UCSB South Pole 1994 cosmic microwave background (CMB) anisotropy data by cross-correlating with templates of infrared dust emission and new high resolution $H_α$ data. $H_α$ data provide rough upper limits on the level of free-free emission in the data sets. The cross-correlation analysis does not contradict a two component foreground emission hypothesis, with the two dust-correlated components being free-free emission and spinning dust emission.

astro-ph↗