Possible relationship between initial conditions for inflation and past geodesic incompleteness of the inflationary spacetime

According to the Borde-Guth-Vilenkin (BGV) theorem an expanding region of spacetime cannot be extended to the past beyond some boundary $\mathcal{B}$. Therefore, the inflationary universe must have had some kind of beginning. However, the BGW theorem says nothing about the boundary conditions on $\m...

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description According to the Borde-Guth-Vilenkin (BGV) theorem an expanding region of spacetime cannot be extended to the past beyond some boundary $\mathcal{B}$. Therefore, the inflationary universe must have had some kind of beginning. However, the BGW theorem says nothing about the boundary conditions on $\mathcal{B}$, or even about its location. Here we present a single-scalar field model of the Two-Measures Theory, where the non-Riemannian volume element $\Upsilon d^4x$ is present in the action. As a result of the model dynamics, an upper bound $\varphi_0$ of admissible values of the scalar field $\varphi$ appears, which sets the position of $\mathcal{B}$ in the form of a spacelike hypersurface $\Upsilon(x)=0$ with a boundary condition: $\Upsilon\rightarrow 0^+$ as $\varphi\rightarrow\varphi_0^{\,\,\,-}$. A detailed study has established that if the initial kinetic energy density $\rho_{kin}^{(in)}$ prevails over initial gradient energy density $\rho_{grad}^{(in)}$ then there is an interval of initial values $\varphi_{in}^{(min)}\leq \varphi_{in}
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Therefore, the inflationary universe must have had some kind of beginning. However, the BGW theorem says nothing about the boundary conditions on $\mathcal{B}$, or even about its location. Here we present a single-scalar field model of the Two-Measures Theory, where the non-Riemannian volume element $\Upsilon d^4x$ is present in the action. As a result of the model dynamics, an upper bound $\varphi_0$ of admissible values of the scalar field $\varphi$ appears, which sets the position of $\mathcal{B}$ in the form of a spacelike hypersurface $\Upsilon(x)=0$ with a boundary condition: $\Upsilon\rightarrow 0^+$ as $\varphi\rightarrow\varphi_0^{\,\,\,-}$. A detailed study has established that if the initial kinetic energy density $\rho_{kin}^{(in)}$ prevails over initial gradient energy density $\rho_{grad}^{(in)}$ then there is an interval of initial values $\varphi_{in}^{(min)}\leq \varphi_{in} &lt;\varphi_0$, where $\rho_{kin}^{(in)}$ and $\rho_{grad}^{(in)}$ cannot exceed the potential energy density and hence the initial conditions necessary for the onset of inflation are satisfied. It is shown that under almost all possible left-handed boundary conditions on $\mathcal{B}$, that is where $\Upsilon\rightarrow 0^-$, the metric tensor in the Einstein frame has a jump discontinuity on $\mathcal{B}$, so the Christoffel connection coefficients are not defined on the spacelike hypersurface $\Upsilon=0$. Thus, if $\varphi_{in}^{(min)}\leq \varphi_{in}&lt;\varphi_0$ and $\rho_{kin}^{(in)}&gt;\rho_{grad}^{(in)}$, then there was an inflationary stage in the history of our Universe and the congruence of timelike geodesics cannot be extended to the past beyond the hypersurface $\Upsilon=0$.</description><identifier>DOI: 10.48550/arxiv.2303.00249</identifier><language>eng</language><subject>Physics - General Relativity and Quantum Cosmology ; Physics - High Energy Physics - Theory</subject><creationdate>2023-03</creationdate><rights>http://creativecommons.org/licenses/by/4.0</rights><oa>free_for_read</oa><woscitedreferencessubscribed>false</woscitedreferencessubscribed></display><links><openurl>$$Topenurl_article</openurl><openurlfulltext>$$Topenurlfull_article</openurlfulltext><thumbnail>$$Tsyndetics_thumb_exl</thumbnail><link.rule.ids>228,230,780,885</link.rule.ids><linktorsrc>$$Uhttps://arxiv.org/abs/2303.00249$$EView_record_in_Cornell_University$$FView_record_in_$$GCornell_University$$Hfree_for_read</linktorsrc><backlink>$$Uhttps://doi.org/10.48550/arXiv.2303.00249$$DView paper in arXiv$$Hfree_for_read</backlink></links><search><creatorcontrib>Kaganovich, Alexander</creatorcontrib><title>Possible relationship between initial conditions for inflation and past geodesic incompleteness of the inflationary spacetime</title><description>According to the Borde-Guth-Vilenkin (BGV) theorem an expanding region of spacetime cannot be extended to the past beyond some boundary $\mathcal{B}$. Therefore, the inflationary universe must have had some kind of beginning. However, the BGW theorem says nothing about the boundary conditions on $\mathcal{B}$, or even about its location. Here we present a single-scalar field model of the Two-Measures Theory, where the non-Riemannian volume element $\Upsilon d^4x$ is present in the action. As a result of the model dynamics, an upper bound $\varphi_0$ of admissible values of the scalar field $\varphi$ appears, which sets the position of $\mathcal{B}$ in the form of a spacelike hypersurface $\Upsilon(x)=0$ with a boundary condition: $\Upsilon\rightarrow 0^+$ as $\varphi\rightarrow\varphi_0^{\,\,\,-}$. A detailed study has established that if the initial kinetic energy density $\rho_{kin}^{(in)}$ prevails over initial gradient energy density $\rho_{grad}^{(in)}$ then there is an interval of initial values $\varphi_{in}^{(min)}\leq \varphi_{in} &lt;\varphi_0$, where $\rho_{kin}^{(in)}$ and $\rho_{grad}^{(in)}$ cannot exceed the potential energy density and hence the initial conditions necessary for the onset of inflation are satisfied. It is shown that under almost all possible left-handed boundary conditions on $\mathcal{B}$, that is where $\Upsilon\rightarrow 0^-$, the metric tensor in the Einstein frame has a jump discontinuity on $\mathcal{B}$, so the Christoffel connection coefficients are not defined on the spacelike hypersurface $\Upsilon=0$. 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Therefore, the inflationary universe must have had some kind of beginning. However, the BGW theorem says nothing about the boundary conditions on $\mathcal{B}$, or even about its location. Here we present a single-scalar field model of the Two-Measures Theory, where the non-Riemannian volume element $\Upsilon d^4x$ is present in the action. As a result of the model dynamics, an upper bound $\varphi_0$ of admissible values of the scalar field $\varphi$ appears, which sets the position of $\mathcal{B}$ in the form of a spacelike hypersurface $\Upsilon(x)=0$ with a boundary condition: $\Upsilon\rightarrow 0^+$ as $\varphi\rightarrow\varphi_0^{\,\,\,-}$. A detailed study has established that if the initial kinetic energy density $\rho_{kin}^{(in)}$ prevails over initial gradient energy density $\rho_{grad}^{(in)}$ then there is an interval of initial values $\varphi_{in}^{(min)}\leq \varphi_{in} &lt;\varphi_0$, where $\rho_{kin}^{(in)}$ and $\rho_{grad}^{(in)}$ cannot exceed the potential energy density and hence the initial conditions necessary for the onset of inflation are satisfied. It is shown that under almost all possible left-handed boundary conditions on $\mathcal{B}$, that is where $\Upsilon\rightarrow 0^-$, the metric tensor in the Einstein frame has a jump discontinuity on $\mathcal{B}$, so the Christoffel connection coefficients are not defined on the spacelike hypersurface $\Upsilon=0$. Thus, if $\varphi_{in}^{(min)}\leq \varphi_{in}&lt;\varphi_0$ and $\rho_{kin}^{(in)}&gt;\rho_{grad}^{(in)}$, then there was an inflationary stage in the history of our Universe and the congruence of timelike geodesics cannot be extended to the past beyond the hypersurface $\Upsilon=0$.</abstract><doi>10.48550/arxiv.2303.00249</doi><oa>free_for_read</oa></addata></record>
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title Possible relationship between initial conditions for inflation and past geodesic incompleteness of the inflationary spacetime
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