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Full-Text Articles in Physical Sciences and Mathematics
Life Beyond The Horizon: The Universe Was Born In A Black Hole, Zahria Patrick
Life Beyond The Horizon: The Universe Was Born In A Black Hole, Zahria Patrick
Undergraduate Research Symposium
It is a widely accepted fact that obtaining information about a black hole is a near-impossible task without being stretched like a spaghetti noodle and trapped in one due to its strong gravitational pull. If the universe exists in a black hole, however, it will mean that it could be possible to survive after crossing its inescapable borders. As surprising as all of this may seem, this theory has existed for quite a while amongst a few different physicists. One person that has shed light on and expanded people’s knowledge of this frightening theory is theoretical physicist, Nikodem Poplawski. The …
Fermi-Bounce Cosmology And Scale-Invariant Power Spectrum, Stephon Alexander, Cosimo Bambi, Antonino Marcianò, Leonardo Modesto
Fermi-Bounce Cosmology And Scale-Invariant Power Spectrum, Stephon Alexander, Cosimo Bambi, Antonino Marcianò, Leonardo Modesto
Dartmouth Scholarship
We develop a non-singular bouncing cosmology using a non-trivial coupling of general relativity to fermionic fields. The usual Big Bang singularity is avoided thanks to a negative energy density contribution from the fermions. Our theory is ghost-free since the fermionic operator that generates the bounce is equivalent to torsion, which has no kinetic terms. The physical system consists of standard general relativity plus a topological sector for gravity, and fermionic matter described by Dirac fields with a non-minimal coupling. We show that a scale invariant power-spectrum generated in the contracting phase can be recovered by suitable choice s of fermion …
A Cyclic Universe Approach To Fine Tuning, Stephon Alexander, Sam Cormack, Marcelo Gleiser
A Cyclic Universe Approach To Fine Tuning, Stephon Alexander, Sam Cormack, Marcelo Gleiser
Dartmouth Scholarship
We present a closed bouncing universe model where the value of coupling constants is set by the dynamics of a ghost-like dilatonic scalar field. We show that adding a periodic potential for the scalar field leads to a cyclic Friedmann universe where the values of the couplings vary randomly from one cycle to the next. While the shuffling of values for the couplings happens during the bounce, within each cycle their time-dependence remains safely within present observational bounds for physically-motivated values of the model parameters. Our model presents an alternative to solutions of the fine tuning problem based on string …
Stability Bounds On Compact Astrophysical Objects From Information-Entropic Measure, Marcelo Gleiser, Nan Jiang
Stability Bounds On Compact Astrophysical Objects From Information-Entropic Measure, Marcelo Gleiser, Nan Jiang
Dartmouth Scholarship
We obtain bounds on the stability of various self-gravitating astrophysical objects using a new measure of shape complexity known as configurational entropy. We apply the method to Newtonian polytropes, neutron stars with an Oppenheimer-Volkoff equation of state, and to self-gravitating configurations of complex scalar field (boson stars) with different self couplings, showing that the critical stability region of these stellar configurations obtained from traditional perturbation methods correlates well with critical points of the configurational entropy with accuracy of a few percent or better.
Constraining The Redshift Evolution Of The Cosmic Microwave Background Blackbody Temperature With Plank Data, I. De Martino, R. Génova-Santos, F. Atrio-Barandela, H. Ebeling, A. Kashlinsky, Dale D. Kocevski, C. J. A. P. Martins
Constraining The Redshift Evolution Of The Cosmic Microwave Background Blackbody Temperature With Plank Data, I. De Martino, R. Génova-Santos, F. Atrio-Barandela, H. Ebeling, A. Kashlinsky, Dale D. Kocevski, C. J. A. P. Martins
Physics and Astronomy Faculty Publications
We constrain the deviation of adiabatic evolution of the universe using the data on the cosmic microwave background (CMB) temperature anisotropies measured by the Planck satellite and a sample of 481 X-ray selected clusters with spectroscopically measured redshifts. To avoid antenna beam effects, we bring all of the maps to the same resolution. We use a CMB template to subtract the cosmological signal while preserving the Thermal Sunyaev–Zeldovich (TSZ) anisotropies; next, we remove galactic foreground emissions around each cluster and we mask out all known point sources. If the CMB blackbody temperature scales with redshift as T(z) …
Supermassive Black Hole Formation At High Redshifts Via Direct Collapse In A Cosmological Context, Jun-Hwan Choi, Isaac Shlosman, Mitchell C. Begelman
Supermassive Black Hole Formation At High Redshifts Via Direct Collapse In A Cosmological Context, Jun-Hwan Choi, Isaac Shlosman, Mitchell C. Begelman
Physics and Astronomy Faculty Publications
We study the early stage of the formation of seed supermassive black holes via direct collapse in dark matter (DM) haloes, in the cosmological context. We perform high-resolution zoom-in simulations of such collapse at high z. Using the adaptive mesh refinement code enzo, we resolve the formation and growth of a DM halo, until its virial temperature reaches ∼104 K, atomic cooling turns on, and collapse ensues. We demonstrate that direct collapse proceeds in two stages, although they are not well separated. The first stage is triggered by the onset of atomic cooling, and leads to rapidly increasing …
Fermi-Bounce Cosmology And The Fermion Curvaton Mechanism, Stephon Alexander, Yi-Fu Cai, Antonino Marcianò
Fermi-Bounce Cosmology And The Fermion Curvaton Mechanism, Stephon Alexander, Yi-Fu Cai, Antonino Marcianò
Dartmouth Scholarship
A nonsingular bouncing cosmology can be achieved by introducing a fermion field with BCS condensation occurring at high energy scales. In this paper we are able to dilute the anisotropic stress near the bounce by means of releasing the gap energy density near the phase transition between the radiation and condensate states. In order to explain the nearly scale-invariant CMB spectrum, another fermion field is required. We investigate one possible curvaton mechanism by involving one another fermion field without condensation where the mass is lighter than the background field. We show that, by virtue of the fermion curvaton mechanism, our …
Transition To Order After Hilltop Inflation, Marcelo Gleiser, Noah Graham
Transition To Order After Hilltop Inflation, Marcelo Gleiser, Noah Graham
Dartmouth Scholarship
We investigate the rich nonlinear dynamics during the end of hilltop inflation by numerically solving the coupled Klein-Gordon-Friedmann equations in an expanding universe. In particular, we search for coherent, nonperturbative configurations that may emerge due to the combination of nontrivial couplings between the fields and resonant effects from the cosmological expansion. We couple a massless field to the inflaton to investigate its effect on the existence and stability of coherent configurations and the effective equation of state at reheating. For parameters consistent with data from the Planck and WMAP satellites, and for a wide range of couplings between the inflaton …
Information-Entropic Stability Bound For Compact Objects: Application To Q-Balls And The Chandrasekhar Limit Of Polytropes, Marcelo Gleiser, Damian Sowinski
Information-Entropic Stability Bound For Compact Objects: Application To Q-Balls And The Chandrasekhar Limit Of Polytropes, Marcelo Gleiser, Damian Sowinski
Dartmouth Scholarship
Spatially-bound objects across diverse length and energy scales are characterized by a binding energy. We propose that their spatial structure is mathematically encoded as information in their momentum modes and described by a measure known as configurational entropy (CE). Investigating solitonic Q-balls and stars with a polytropic equation of state P=Kργ, we show that objects with large binding energy have low CE, whereas those at the brink of instability (zero binding energy) have near maximal CE. In particular, we use the CE to find the critical charge allowing for classically stable Q-balls and the Chandrasekhar limit for white dwarfs (γ=4/3) …
Gauge Field Preheating At The End Of Inflation, J. Tate Deskins, John T. Giblin Jr., Robert R. Caldwell
Gauge Field Preheating At The End Of Inflation, J. Tate Deskins, John T. Giblin Jr., Robert R. Caldwell
Dartmouth Scholarship
Here we consider the possibility of preheating the Universe via the parametric amplification of a massless, U(1) abelian gauge field. We assume that the gauge field is coupled to the inflaton via a conformal factor with one free parameter. We present the results of high-resolution three-dimensional simulations of this model and show this mechanism efficiently preheats the Universe to a radiation-dominated final state.
Information Content Of Spontaneous Symmetry Breaking, Marcelo Gleiser, Nikitas Stamatopoulos
Information Content Of Spontaneous Symmetry Breaking, Marcelo Gleiser, Nikitas Stamatopoulos
Dartmouth Scholarship
We propose a measure of order in the context of nonequilibrium field theory and argue that this measure, which we call relative configurational entropy (RCE), may be used to quantify the emergence of coherent low-entropy configurations, such as time-dependent or time-independent topological and nontopological spatially extended structures. As an illustration, we investigate the nonequilibrium dynamics of spontaneous symmetry breaking in three spatial dimensions. In particular, we focus on a model where a real scalar field, prepared initially in a symmetric thermal state, is quenched to a broken-symmetric state. For a certain range of initial temperatures, spatially localized, long-lived structures known …
Fine-Tuning Solution For Hybrid Inflation In Dissipative Chaotic Dynamics, Rudnei O. Ramos
Fine-Tuning Solution For Hybrid Inflation In Dissipative Chaotic Dynamics, Rudnei O. Ramos
Dartmouth Scholarship
We study the presence of chaotic behavior in phase space in the preinflationary stage of hybrid inflation models. This is closely related to the problem of initial conditions associated with these inflationary types of model. We then show how an expected dissipative dynamics of fields just before the onset of inflation can solve or ease considerably the problem of initial conditions, driving the system naturally toward inflation. The chaotic behavior of the corresponding dynamical system is studied by computation of the fractal dimension of the boundary in phase space separating inflationary from noninflationary trajectories. The fractal dimension for this boundary …
Comparing The Sfi Peculiar Velocities With The Pscz Gravity Field: A Velmod Analysis, E. Branchini, W. Freudling, L. N. Da Costa, C. S. Frenk, R. Giovanelli, M. P. Haynes, J. J. Salzer, G. Wegner, I. Zehavi
Comparing The Sfi Peculiar Velocities With The Pscz Gravity Field: A Velmod Analysis, E. Branchini, W. Freudling, L. N. Da Costa, C. S. Frenk, R. Giovanelli, M. P. Haynes, J. J. Salzer, G. Wegner, I. Zehavi
Dartmouth Scholarship
We compare the peculiar velocities derived from the I-band Tully–Fisher (TF) relation for 989 field spiral galaxies in the SFI catalogue with the predicted velocity field derived from the IRAS PSCz galaxy redshift survey. We assume linear gravitational instability theory and apply the maximum likelihood technique, VELMOD to SFI galaxies within a redshift cz LG =6000 km s−1. The resulting calibration of the TF relation is consistent with a previous, independent calibration for a similar sample of spirals residing in clusters. Our analysis provides an accurate estimate of the quantity βI ≡ Ωm0.6 …
Shortcuts In The Fifth Dimension, Robert Caldwell, David Langlois
Shortcuts In The Fifth Dimension, Robert Caldwell, David Langlois
Dartmouth Scholarship
If our Universe is a three-brane embedded in a five-dimensional anti-de Sitter spacetime, in which matter is confined to the brane and gravity inhabits an infinite bulk space, then the causal propagation of luminous and gravitational signals is in general different. A gravitational signal traveling between two points on the brane can take a “shortcut” through the bulk, and appear quicker than a photon traveling between the same two points along a geodesic on the brane. Similarly, in a given time interval, a gravitational signal can propagate farther than a luminous signal. We quantify this effect, and analyze the impact …
Affinity For Scalar Fields To Dissipate, Arjun Berera, Rudnei O. Ramos
Affinity For Scalar Fields To Dissipate, Arjun Berera, Rudnei O. Ramos
Dartmouth Scholarship
The zero-temperature effective equation of motion is derived for a scalar field interacting with other fields. For a broad range of cases, involving interaction with as few as one or two fields, dissipative regimes are found for the scalar field system. The zero-temperature limit constitutes a baseline effect that will be prevalent in any general statistical state. Thus, the results found here provide strong evidence that dissipation is the norm not the exception for an interacting scalar field system. For application to inflationary cosmology, this provides convincing evidence that warm inflation could be a natural dynamics once proper treatment of …
Recovery Of The Power Spectrum Of Mass Fluctuations From Observations Of The Ly Alpha Forest, Rac Croft, Dh Weinberg, N Katz, L Hernquist
Recovery Of The Power Spectrum Of Mass Fluctuations From Observations Of The Ly Alpha Forest, Rac Croft, Dh Weinberg, N Katz, L Hernquist
Astronomy Department Faculty Publication Series
We present a method to recover the shape and amplitude of the power spectrum of mass fluctuations, P(k), from observations of the high-redshift Lyα forest. The method is motivated by the physical picture that has emerged from hydrodynamic cosmological simulations and related semianalytic models, in which typical Lyα forest lines arise in a diffuse, continuous, fluctuating intergalactic medium. The thermal state of this low-density gas (δρ/ρ 10) is governed by simple physical processes, which lead to a tight correlation between the Lyα optical depth and the underlying matter density. To recover the mass power spectrum, we (1) …
Intergalactic Helium Absorption In Cold Dark Matter Models, Rac Croft, Dh Weinberg, N Katz, L Hernquist
Intergalactic Helium Absorption In Cold Dark Matter Models, Rac Croft, Dh Weinberg, N Katz, L Hernquist
Astronomy Department Faculty Publication Series
Observations from the Hopkins Ultraviolet Telescope and the Hubble Space Telescope have recently detected He II absorption along the lines of sight to two high-redshift quasars. We use cosmological simulations with gas dynamics to investigate He II absorption in the cold dark matter (CDM) theory of structure formation. We consider two Ω = 1 CDM models with different normalizations and one open universe (Ω0 = 0.4) CDM model. The simulations incorporate the photoionizing UV background spectrum computed by Haardt & Madau, which is based on the output of observed quasars and reprocessing by the Lyα forest. The simulated …
Testing Cosmological Models Against The Abundance Of Damped Lyman-Alpha Absorbers, Jp Gardner, N Katz, Dh Weinberg, L Hernquist
Testing Cosmological Models Against The Abundance Of Damped Lyman-Alpha Absorbers, Jp Gardner, N Katz, Dh Weinberg, L Hernquist
Astronomy Department Faculty Publication Series
We calculate the number of damped Lyα absorbers expected in various popular cosmological models as a function of redshift and compare our predictions with observed abundances. The Press-Schechter formalism is used to obtain the distribution of halos with circular velocity in different cosmologies, and we calibrate the relation between circular velocity and absorption cross section using detailed gasdynamical simulations of a standard cold dark matter (CDM) model. Because of this calibration, our approach makes more realistic assumptions about the absorption properties of collapsed objects than previous, analytic calculations of the damped Lyα abundance. CDM models with Ω0 = 1, …